Calibrating X-ray binary luminosity functions via optical reconnaissance I. The case of M83
Qiana Hunt, Elena Gallo, Rupali Chandar, Paula Johns Mulia, Angus Mok, Andrea Prestwich, Shengchen Liu
DD RAFT VERSION F EBRUARY
16, 2021Typeset using L A TEX twocolumn style in AASTeX63
Calibrating X-ray binary luminosity functions via optical reconnaissance I. The case of M83 Q IANA H UNT , E LENA G ALLO , R UPALI C HANDAR , P AULA J OHNS M ULIA , A NGUS M OK , A NDREA P RESTWICH , AND S HENGCHEN L IU Department of Astronomy, University of Michigan, 1085 S University, Ann Arbor, MI 48109, USA Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606, USA Department of Physics and Astronomy, University of Toledo, 2801 W Bancroft Street, Toledo, OH 43606, USA Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Department of Astronomy, School of Physics, Peking University, Beijing 100871, China
ABSTRACTBuilding on recent work by Chandar et al. (2020), we construct X-ray luminosity functions (XLFs) for differ-ent classes of X-ray binary (XRB) donors in the nearby star-forming galaxy M83 through a novel methodology:rather than classifying low- vs. high-mass XRBs based on the scaling of the number of X-ray sources withstellar mass and star formation rate, respectively, we utilize multi-band
Hubble Space Telescope imaging datato classify each
Chandra -detected compact X-ray source as a low-mass (i.e. donor mass < ∼ M (cid:12) ), high-mass(donor mass > ∼ M (cid:12) ) or intermediate-mass XRB based on either the location of its candidate counterparton optical color-magnitude diagrams or the age of its host star cluster. In addition to the the standard (singleand/or truncated) power-law functional shape, we approximate the resulting XLFs with a Schechter function.We identify a marginally significant (at the -to- σ level) exponential downturn for the high-mass XRB XLF, at (cid:96) (cid:39) . +0 . − . (in log CGS units). In contrast, the low- and intermediate-mass XRB XLFs, as well as the totalXLF of M83, are formally consistent with sampling statistics from a single power-law. Our method suggestsa non-negligible contribution from low- and possibly intermediate-mass XRBs to the total XRB XLF of M83,i.e. between 20 and 50%, in broad agreement with X-ray based XLFs. More generally, we caution againstconsiderable contamination from X-ray emitting supernova remnants to the published, X-ray based XLFs ofM83, and possibly all actively star-forming galaxies. Keywords:
X-rays: binaries – X-rays: galaxies – stars: luminosity function, mass function – techniques: photo-metric INTRODUCTIONIn the absence of a bright active galactic nucleus (AGN),X-ray binaries (XRBs) dominate the point source X-rayemission of a galaxy, with only minor contributions fromcoronally active binaries, cataclysmic variables, unresolvedsources and supernova remnants (Fabbiano 2006; Borosonet al. 2011, and references therein). Owing to their dif-ferent formation and evolutionary time scales, XRBs withlow- and high-mass donors (hereafter referred to as LMXBsand HMXBs, where the former refers to donor masses be-low < ∼ M (cid:12) , whereas latter refers to donors in excess of > ∼ M (cid:12) ) can be expected to trace the integrated stellar con-tent and recent star formation output of their host galaxy, re-spectively. Indeed, seminal work by Grimm et al. (2003),based on ASCA and early
Chandra X-ray Observatory datafor the Milky Way Galaxy and the Magellanic Clouds (seealso Ranalli et al. 2003) first established a quantitative scalingbetween the integrated X-ray luminosity of HMXBs with thehost galaxy star formation rate (SFR). In a follow-up study, Gilfanov & Grimm (2004) crystallized the notion of a “uni-versal” HMXB X-ray luminosity function (XLF) for star-forming galaxies, the normalization of which is proportionalto the host galaxy SFR. Along the same lines, using
Chandra data for 11 nearby galaxies, Gilfanov (2004) demonstratedthat the total number of LMXBs and their integrated X-rayluminosity are proportional to the stellar mass ( M (cid:63) ) budgetof the host galaxy, thereby establishing a “universal” XLF forLMXBs (see also Kim & Fabbiano 2004).Since these pioneering works, quantitative investigationsof the scaling relations between the HMXB and LMXB XLFsand host galaxy properties have progressively sharpened,largely thanks to several Msec of sub-arcsec resolution X-ray imaging data accumulated by Chandra for tens of nearbygalaxies. Updated XRB XLFs and their scaling relations areroutinely employed for a variety of purposes. For example,the total X-ray luminosity is taken as a reliable SFR proxy indistant, star-forming galaxies (Mineo et al. 2014), and the ex-pected total X-ray luminosity in XRBs (Lehmer et al. 2010) a r X i v : . [ a s t r o - ph . H E ] F e b can be used to argue in favor or against a low-luminosityAGN on a statistical basis. Nevertheless, perhaps not surpris-ingly, a larger degree of complexity has also emerged fromthis wealth of data.There is reason to question the supposed universality ofthe XRB XLFs and their scaling relations. From a theoret-ical standpoint, large variations in the LMXB XLFs are tobe expected with stellar age, whereas metallicity effects areexpected to drive variations in the HMXB XLF (Fragos et al.2013). The notion that both may have sizable effects on theXRB XLFs is consistent with the claimed redshift evolutionof L X / M (cid:63) and L X /SFR, whereby the cosmic decline in meanstellar age and metallicity would be responsible for the in-ferred increase of both ratios with z (Lehmer et al. 2016;Aird et al. 2017, and references therein). However, a quanti-tative assessment of the role of age and metallicity in shapingthe XRB XLFs functional form is inevitably challenging, asdeep, high-statistics XLFs have only been assembled fornearby galaxies spanning a relatively limited range in both(see, e.g., Irwin et al. 2004; Colbert et al. 2004; Kaaret et al.2011; Prestwich et al. 2013; Plotkin et al. 2014; Basu-Zychet al. 2016; Tzanavaris et al. 2016; Wang et al. 2016).There may also be issues with the overall approach to char-acterizing XRB XLFs. In an effort to isolate the LMXB pop-ulation, even the most comprehensive studies select massiveelliptical galaxy samples, with large numbers of sources andnegligible SFR levels, so as to ensure virtually zero HMXBcontamination. Conversely, HMXB XLF studies focus onhigh specific SFR (sSFR, defined as the ratio SFR/ M (cid:63) ) galax-ies so as to minimize the contribution from LMXBs. Al-though practical, these selection strategies may affect the ro-bustness of the inferred XLFs, or, at a minimum, pose a chal-lenge to their claimed universality. For one, late-type galax-ies with moderate sSFRs are excluded targets, as they areguaranteed to have a mixed LMXB/HMXB population. This,however, also means that we have no reliable knowledge ofthe LMXB XLF in star-forming galaxies (to this end, it isperhaps indicative that, when Mineo et al. 2012 attempted tocorrect their inferred HMXB XLF for possible LMXBs con-tamination using the XLF derived from elliptical galaxies,they obtained negative counts). Since the LMXB contribu-tion theoretically depends on mean stellar age, it is reason-able to expect that early and late-type galaxies may exhibitdifferent correlations with stellar mass, as well as differentspatial distributions.Lastly, there are indications that globular cluster (GC) spe-cific frequency may also affect the shape and normalizationof the LMXB XLF (Sivakoff et al. 2004; Humphrey & Buote2008; Kim et al. 2009; Zhang et al. 2011; Peacock & Zepf2016); this is not surprising, since field vs. GC LMXBslikely have different origins and evolutionary paths. If so, then the higher specific frequency of GCs in massive ellipti-cals could yield higher XLF normalizations than for LMXBsin late-type galaxies. Additionally, metallicity can affect theXLF of GC XRBs, as red GCs may be more often associatedwith bright LMXBs (Jord´an et al. 2004; Kim et al. 2006;Sivakoff et al. 2007; Peacock et al. 2017; Kim et al. 2013;Luan et al. 2018).In a recent endeavor to properly characterize the XLFs ofboth HMXBs and LMXBs in late-type galaxies, Lehmeret al. (2019, hereafter L19) fit the XLFs of 38 nearbygalaxies spanning a broad range of SFR and M (cid:63) with aglobal model which fits simultaneously for the contribu-tions from HMXBs, LMXBs and background sources usingsub-galactic SFR and stellar mass maps (see also Lehmeret al. 2017, and references therein, for other examples ofsub-galactic modeling studies). This novel and powerfulapproach reveals a smooth, progressive decline in the XLFnormalization per unit SFR, accompanied by a decrease innormalization at the bright-end with increasing sSFR, i.e.,as the dominant contribution to the XRB population shiftsfrom LMXBs to HMXBs. The study also unveils furtherinteresting subtleties, such as an intriguing flattening of theHMXB XLF between − erg s − and a possi-ble disagreement in the LMXB XLF slopes below andabove erg s − compared to the results obtained forelliptical galaxies only (Zhang et al. 2012). This further em-phasizes the need to move beyond a one-size-fits-all XLFmodeling concept.Motivated by the same kind of considerations, this Pa-per follows a very different approach to disentangling theLMXB and HMXB XLFs: by leveraging Hubble Space Tele-scope (HST) multi-band imaging data, we directly classifythe optical counterparts to Chandra -detected point-like X-ray sources in the field of view of the target galaxy. Thistechnique, which was developed for and tested on the nearbyspiral galaxy M101 by Chandar et al. (2020, hereafter C20),hinges on the notion that, on average, HST imaging enablesthe direct detection of XRB donor stars down to a givendistance-dependent mass limit (e.g., down to ∼ (cid:12) at thedistance of M101). By construction, this procedure does notrely on underlying assumptions about the relationship be-tween a galaxy’s XRB populations and their local environ-ments; it also enables us, for the first time, to elucidate therole of intermediate-mass XRBs, i.e. XRBs with donors inthe ∼ − M (cid:12) range.Here, we introduce a number of improvements upon C20and apply our revised methodology to M83 (NGC 5236).M83 is a face-on (i = 24 ◦ ; Talbot et al. 1979) spiral galaxywith M (cid:63) ∼ × M (cid:12) , a moderate SFR of ≈ . M (cid:12) yr − (L19), and no significant AGN contribution in the nuclear re-gion. At a distance of 4.66 Mpc (Saha et al. 2006), yielding adistance modulus of 28.32 and a physical scale of 1 (cid:48)(cid:48) ≈
22 pc,it is closer than M101 (6.4 ± (cid:48)(cid:48) ≈
31 pc).Furthermore, the Galactic absorption is low along the line ofsight to M83 (N H = 4 × cm − ; Kalberla et al. 2005),making it ideal for an optical photometric study of X-raysource populations.In this work, we present a fully classified catalog of X-ray sources in M83 that builds upon that published in L19.Each source is classified on a rigorous, source-by-source ba-sis as either a low-, intermediate-, or high-mass XRB, a back-ground galaxy, or a supernova remnant (SNR). We use theseclassifications to construct “uncontaminated” XLFs for eachXRB population. Our main goal is to assess the shape ofthe XLFs and establish whether or not there is evidence for astatistically significant cut-off at the bright end, the presenceof which has been widely debated (e.g. Zhang et al. 2012;Mineo et al. 2012; C20). We are also interested in the nor-malization of each XLF, and how well it matches predictionsfrom the global model presented by L19 and other studies.The rest of this work is organized as follows: in §2, we iden-tify the optical counterparts to X-ray sources in M83, separat-ing out contamination (AGN, quasars, and SNR, §2.4) fromthe XRBs, and we estimate the masses of XRBs, which mayappear as either an individual donor star or existing withina parent cluster; in §3, we investigates the spatial distribu-tion of the classified XRBs; in §4, we present Schechter andpower-law function fits to the the XRB XLFs and assess thepresence of a downturn or cut-off; and finally in §5, we com-pare the normalizations of our optical data-based XLFs withthe literature (namely, L19). SOURCE CLASSIFICATION2.1.
X-ray Source Catalog
As our primary X-ray point-source list, we adopt the M83catalog constructed from deep
Chandra
ACIS imaging databy L19, which examines a total of 38 galaxies. The L19study includes a thorough estimate of the completeness ofthe detected X-ray point sources, which is crucial to our pur-poses. The
Chandra data were reduced following the meth-ods detailed in Lehmer et al. (2017): for each galaxy, theanalysis was restricted to data sets with aim points within5 (cid:48) of the nominal center position, ensuring a sharp pointspread function for the nuclear regions which tend to be themost crowded. The source detection and parameter extrac-tion were performed within 0.5-7 keV, where ACIS is bestcalibrated.
Figure 1.
An optical image of M83 taken with by theWFC3 camera on HST (Blair et al. 2014, available at https://archive.stsci.edu/prepds/m83mos ). The B -band is shown in blue, V -band in green, and I -band in red. The 7-pointingmosaic covers ≈ square arcminutes (75.2 Mpc ) The locations of allX-ray sources from the L19 catalog (adopted here and shown as greencircles) and those from the version 2.0 release of the Chandra SourceCatalog (green X’s) are shown. The galactic footprint adopted by L19tracing the K s ≈ mag arcsec − galactic surface brightness (see Jarrettet al. 2003) is outlined in white for comparison. Out of a total of 456 point-like sources brighter than erg s − , we restrict our analysis to the 325 objects that fallwithin the M83 HST footprint, shown in Figure 1. For com-parison, L19 restricts its XLF fitting to those 363 sources thatare located within an ellipse that traces the K s ≈ magarcsec − galactic surface brightness, outlined in white.Long et al. (2014) also published a catalog of X-ray pointsources in M83 based on a partial set of the data used in L19.The main focus of their work was to detect a sample of SNRsusing multi-wavelength observations. In §2.4 we use clas-sification information provided in the Long catalog to elimi-nate SNRs and some background AGN from our initial X-raypoint source catalog.2.2. Combining X-ray and Optical Data
HST observations of M83 were taken with theWFC3/UVIS instrument, spanning seven fields that eachcover approximately 162 (cid:48)(cid:48) × (cid:48)(cid:48) for a total mosaic areaof ∼
43 square arcminutes. All observations were obtained By comparison the
Chandra
Source Catalog Release 2 (CSC 2.0; Evanset al. 2020) returns 463 unique, significant X-ray sources within 12. (cid:48)(cid:48) between August 2009 and September 2012 by R. O’Connell(Prop ID. 11360) and W. Blair (Prop ID. 12513), with ex-posure times ranging from ∼ . − . ks for each im-age. Images were downloaded from the Hubble LegacyArchive (HLA ). In general, BVI images are created usingthe F438W, F547M, and F814W filters. The central field,which includes the galaxy nucleus, uses the broader F555W V -band filter, rather than F547M. We also use U-band im-ages (F336W) to help calculate cluster ages (see §2.5).Figure 1 shows a BVI mosaic of all seven M83 HST fields(available on HLA; Blair et al. 2014). The mosaic com-bines the two different V-band filters used for the centralfield (F555W) and the 6 remaining fields (F547M) by scalingthe F555W data to match the scaling on F547M. We utilizethis single, cohesive V-band image for correcting the relativeastrometry between Chandra and HST observations. 6 X-ray sources whose HST counterparts are clearly backgroundgalaxies (i.e., morphology and color; see §2.4 for details) areidentified as reference ‘AGN’ for the astrometric correction.For these objects, we calculate a median relative positionaloffset of ∼ (cid:48)(cid:48)
079 and 0. (cid:48)(cid:48)
229 along the x- and y- axes of theHST image respectively, with standard deviations of 0. (cid:48)(cid:48) (cid:48)(cid:48)
Candidate Optical Counterparts
Optical counterparts to XRBs in M83 can be either donorstars or host stellar clusters. We use the IRAF DAOFINDtask to detect all point-like sources, down to the faintest lev-els, on the composite V-band image. We perform aperturephotometry with the IRAF PHOT task using a 3 pixel aper-ture radius for each detected source, with the local back-ground level determined in an annulus with radii between 20and 25 pixels. Due to the rescaling of the F555W field for thecreation of the mosaic, which may have introduced calibra-tion errors, photometry of all detected sources is performedon individual images rather than on the mosaic. Aperture cor-rections of -0.48 mag (V) and -0.61 mag (I) were determinedby taking the median difference between the magnitude in3 and 20 pixel apertures of several relatively bright, isolatedstars with smooth radial profiles that flatten towards the back-ground sky magnitude with increasing aperture radius.An additional correction term of -0.06 mag is added to eachfilter to correct for the small amount of flux missing from a20 pixel aperture (see Encircled Energy Fractions from 20pixels to infinity in Deustua et al. 2017). These instrumentalmagnitudes are converted to the VEGAMAG system by ap-plying the zero-point magnitude for each filter as reported inTable 2 of Deustua et al. (2017). http://hla.stsci.edu/ Candidate optical counterparts to each X-ray source areinitially selected by applying a proximity criterion to the X-ray source positions. We define 1- and 2- σ positional un-certainty radii for each source by adding in quadrature thestandard deviation in the Chandra-HST positional offsets andthe X-ray positional uncertainty (see Figure A.2). The lat-ter depends sensitively on the X-ray source distance fromthe observation aim-point, as well as the number of counts.We adopt Equations 14 and 12 in Kim et al. (2007) to cal-culate the 68% and 95% confidence positional uncertaintyfor each source, as a function of total counts (C) and off-axis angle (OAA) – both of which are available in the L19catalog. An additional uncertainty term is added to the 1-and 2- σ radii calculated above, due to the slight rotationsbetween the fields and the mosaic. This is an improvementon the method used in C20, where the 1- and 2- σ positionaluncertainties in M101 were assume to be circles with a ra-dius of . (cid:48)(cid:48) and . (cid:48)(cid:48) for each X-ray point source. A fi-nal correction is made to the absolute optical magnitudes ofeach source to account for foreground extinction. Using therelation N H (cm − ) = (2 . ± . × A V (G¨uver &¨Ozel 2009) with the known Galactic absorption towards M83(Long et al. 2014), we find an extinction of A V ≈ . mag,corresponding to a reddening of E(B − V) ≈ .
054 mag (Mathis 1990). We do not account for extinction intrinsicto each source, though we employ a confidence flag scheme(see Table A.2) to indicate sources that may be particularlysusceptible to the effects of reddening and obscuration withinM83. We test the impact of this assumption on our results in§2.6. 2.4.
Non-X-ray Binary Sources
Contributions from stellar sources such as coronally activebinaries and cataclysmic variables are completely negligi-ble above L X (cid:39) erg s − (Boroson et al. 2011), thecompleteness limit of our sample (L19). Hence, the mainsources of contamination are background AGN and quasars,and bright SNRs within the host galaxy. We address them inturn below. Our approach differs substantially from all otherXLF investigations in that we aim to directly identify andreject all contaminants, whereas published works almost ex-clusively correct for AGN contamination statistically, usingthe known Cosmic X-ray Background log N − log S .In an extended, multi-wavelength spectral and temporalanalysis of M83’s X-ray point-source population, Long et al.(2014) classified a significant fraction of the point sourcepopulation as SNR. These were classified based on variabil-ity, spectral hardness, [S II]:H α line ratios or strong [O III]emission, and cross-referencing with earlier SNR catalogsusing Chandra , XMM-Newton , Magellan, the Australia Tele-scope Compact Array, and the sites of historical supernovae
Figure 2.
The measured X-ray luminosity vs. hardness ratio of sourcesin M83, with the subset classified as SNRs (red +’s), AGN (yellow circles),and XRBs (green X’s) by Long et al. (2014) indicated. SNRs occupy a softerportion of this parameter space that does not overlap with AGN or XRBs.The hardness ratio is defined as the difference between the hard band (2-7 keV; H) and the soft band (0.5-1.2 keV; S)
Chandra counts over their sum.We define a selection criteria that cuts sources with X-ray log luminositiesbelow 37.5 and hardness ratios less than - . , the limit softer than which60% of the sources are SNRs, to minimize contamination from unclassifiedSNRs in our sample. (Wood & Andrews 1974; Soria & Wu 2003; Maddox et al.2006; Dopita et al. 2010; Blair et al. 2012; Ducci et al. 2013).Long’s investigation provides us with the rare opportunityto construct a set of X-ray based diagnostic criteria that canbe used to reject contaminants that have not been previouslyclassified, and that are typically ignored in other studies. Outof the 87 X-ray sources identified by Long et al. (2014) asSNRs or SNR candidates, 76 are included in the HST foot-print. Of these, 55 have available X-ray soft and hard counts( S and H , corresponding to the 2-7 keV and 0.5-1.2 keVbands, respectively) in the CSC R2. We obtain a hardnessratio, defined as the difference between H and S over the to-tal counts in both, for each source where available. We plotthe measured X-ray luminosity, L X against the hardness ra-tio in Figure 2. The value of L X for each source is takenfrom L19, in which luminosities are obtained from 0.5-8 keVX-ray fluxes. This energy range allows for a straightforwardcomparison with (most of) the literature (see L19 for details).The Long et al. (2014) SNR (red + ’s), AGN (orange cir-cles) and XRB (green X’s) classifications are indicated wheregiven.We find that the majority of SNRs belong to a distinctparameter space that is well-separated from other X-raysources. Based on this phenomenological approach, weadopt minimum L X and HR cuts to automatically select outcandidate SNRs in our catalog. Our L X cut is set to thehighest L X of the Long SNRs in our sample, or (cid:96) ≤ . , where (hereafter) (cid:96) represents logarithmic X-ray luminositiesin units of erg s − . The minimum HR is chosen such that60% of all sources softer than this limit are Long-classifiedSNRs, which corresponds to HR ≤ − . . Excluding (76)X-ray sources classified by Long et al. (2014) as candidateSNRs, an additional 27 sources meet our criteria. All 27X-ray sources with these properties are rejected from ourcatalog. We assess the impact of this on the XLFs in §5.2and the Appendix.After removing SNRs, the remaining population of con-taminants consist of background AGN and quasars. The restmay be identified through catalog cross-referencing and ananalysis of optical properties. Long et al. (2014) classifyseveral foreground and background contaminants based onX-ray hardness, X-ray-to-optical flux ratios, color, and priorcatalogs. We classify additional contaminants on the basisof their morphology. Background galaxies can typically beidentified by their distinct morphologies, including featuressuch as nuclei, spiral arms and/or disks, with the exception ofdistant quasars, which appear in optical images as primarilyred sources with extended radial profiles. In total, we removefrom our sample 3 visually identifiable background AGN and2 sources identified as AGN in Long et al. (2014). We alsoremove 2 candidate quasars.2.5. Classification of XRBs Based on Parent Cluster Age
We expect to find some XRBs in our sample still occu-pying their parent star clusters. In early-type galaxies, be-tween 25-70% of LMXBs are found in ancient globular clus-ters (Angelini et al. 2001; Kundu et al. 2002; Jord´an et al.2004; Kundu et al. 2007; Humphrey & Buote 2008; Peacock& Zepf 2016). In spiral and star-forming galaxies, however,the fraction of LMXBs found in globular clusters remainsquite uncertain, albeit significantly lower: the dwarf starburstNGC 4449 and the spiral galaxy M101 each has only a singleLMXB in a globular cluster (Rangelov et al. 2011; C20). Thefraction of HMXBs in spirals which still reside in their par-ent clusters is also poorly known but higher, with ≈ % ofXRBs in M101 (C20) and ≈ % in the Antennae (Rangelovet al. 2012) found in clusters younger than a few 100 Myr.Because of their high stellar density, the donor stars feed-ing XRBs that reside within compact stellar clusters cannotbe identified individually at the distance of M83. However,the ages of parent clusters can be used as a proxy for esti-mating the masses of the donor stars in XRBs, since the mostmassive surviving stars within a cluster are the most dynam-ically active, and hence the most likely to form tight bina-ries. High mass stars ( ≥ M (cid:12) ) have hydrogen burning life-times of only ∼ Myr, and intermediate-mass ( (cid:38) M (cid:12) )stars have lifetimes of ∼ Myr. This means that clustersolder than ∼ Myr only contain stars less massive than M (cid:12) and may only host LMXBs, while clusters youngerthan ∼
10 Myr are likely to host HMXBs. We assume thatclusters with ages between 10 and 400 Myr host IMXBssince the most massive stars remaining in clusters in this agerange (3-8 M (cid:12) ) have intermediate mass.To identify possible clusters among our candidates, wecompare our optical matches for each XRB to a catalog ofM83 clusters previously published by Chandar et al. (2014).This catalog selected clusters to be broader than the pointspread function (PSF) based on the FWHM of the radial pro-file, as well as the Concentration Index, defined as the differ-ence in magnitudes measured for a 1 and 3 pixel aperture ra-dius (see Chandar et al. 2014 for details about selection). Wefind that a total of 12 ( ∼ % of the total) XRBs in M83 arefound within a compact stellar cluster. We compare the col-ors measured for the XRB-cluster hosts with those predictedby the Bruzual & Charlot (2003) stellar evolution models atsolar metallicity in Figure 3. These models start at 1 Myr(upper left) and go through 13 Gyr (lower-right), with keyages marked along the model track. The arrow indicates thedirection the colors of clusters would move due to reddeningby dust. XRB cluster hosts have a range of colors and, hence,ages.While the color-color diagram provides a good visual com-parison of cluster colors with model predictions, the age ofeach cluster is estimated using a spectral energy distributionfitting method, where we fit for the best combination of ageand reddening, as described in Chandar et al. (2014). Mag-nitudes measured in the UBVI and H α filters for each clusterare fit to predictions from Bruzual & Charlot (2003) using astandard χ minimization; see Chandar et al. (2014) for de-tails. The best fit age for each cluster is recorded in Table A.2and used to classify each XRB: HMXBs have parent clusters < Myr, IMXBs have parent clusters with best fit ages be-tween − Myr and LMXBs have parent cluster ages > Myr.2.6.
Classification of XRBs Based on Donor Star Mass
The majority of X-ray sources contain at least one opti-cal point source within their 2- σ radius, with several coinci-dent with multiple candidates. The most likely XRB donor ischosen on a case-by-case basis. In general, priority is givento brighter sources that fall within or closest to the 1- σ ra-dius. In most cases, it is not necessary to identify the exactdonor of an XRB with several bright candidates, so long asthe candidates fall within the same mass regime. For casesin which multiple sources are detected over a range of pos-sible donor masses, intermediate-mass sources are deprior-itized, since few IMXBs have been identified in the MilkyWay compared to high- and low-mass counterparts. Whengiven the option between high-mass and low-mass poten-tial counterparts, high-mass stars are prioritized as the most Figure 3.
Measured U − B vs V − I colors of XRB host clusters com-pared with predictions for the color evolution of clusters from the Bruzual &Charlot (2003) models. Different model ages are marked by black triangles,with blue points indicating HMXBs, green indicating IMXBs, and red indi-cating LMXBs, moving from top left to bottom right. The arrow representsthe direction of reddening expected from a Milky Way-type extinction curvewith A V = 1 . likely donor, given the relative rarity of both high-mass starsand XRBs within galaxies (see §2.7).We directly estimate the masses of bright donor candi-dates by comparing them to the theoretical evolutionary masstracks for solar metallicity stars from the Padova models ona color-magnitude diagram (CMD, Figure 4), using the masslimits defined in §1 (LMXB ≤ M (cid:12) , HMXB ≥ M (cid:12) ).C20 find that archival HST images of M101 are deep enoughto see stars down to 3 M (cid:12) at a distance of 6.4 ± M (cid:12) line, with a few sourcesfalling below. This suggests that, indeed, we are able to de-tect sources down to the minimum threshold required to iden-tify the donor stars of HMXBs within M83. On the otherhand, X-ray sources that lack an optical counterpart likelyhave stellar components that fall beneath the observable mag-nitude threshold, suggesting the system is a LMXB.The left and right panels of Figure 4 compare the V-I colorsand B-V colors of the XRBs. We note that we are unable toextract B-band magnitudes from all of the point sources inour sample since the observations are not as deep in the B-band as they are in the V-band. Nevertheless, it is the absolute V -band luminosity that is most important for estimating themasses of the donor stars. Figure 4.
Left: V − I vs. V CMD of XRB donor star candidates identified in M83 (black points). These are compared with theoreticalevolutionary tracks modeled at solar metallicity (Bertelli et al. 1994; Girardi et al. 2010; Marigo et al. 2017). Overall, donor stars in M83appear to be detectable with the HST down to > ∼ M (cid:12) . Right: B − V vs. V CMD of candidate XRB donor stars. In addition, all X-ray brightMilky Way HMXBs and LMXBs having measured B and V magnitudes are shown as blue and red points, respectively, as identified by Liuet al. (2006) and Liu et al. (2007). In order to investigate the potential effects of extinctionof the donor stars in our X-ray binaries, we can comparethe measured U − B vs. V − I colors of donor stars withpredicted stellar tracks, following the procedure in Kim et al.(2017). Reddening will move the observed colors off themodel tracks and allow for an estimate of E ( B − V ) . Thismethod requires photometric errors to be less than ≈ . magin each band, so it is only applicable to a subsection of donorstars. The colors of the donor stars that satisfy this require-ment indicate low typical E ( B − V ) values of ∼ . to . mag, which is reasonable given that M83 is orientednearly face-on. This level of extinction would only affect theclassification of a few IMXBs, in the sense that they wouldjust exceed the M (cid:12) theshold of the model tracks, but oth-erwise does not have much impact on our classifications.In total, 214 of the 325 X-ray sources that fall within theHST footprint are classified as XRBs using the methods de-scribed, 12 of which exist within compact stellar clusters. Wepresent these sources, their positions, X-ray luminosity, op-tical colors, and source classification in Table A.2 and Fig-ure A.2. For these X-ray sources, we find 30 are LMXBs,120 are HMXBs, and 64 fall in the intermediate mass rangebetween the two limits. For each of the panels in Figure A.2,the 1- and 2- σ positional uncertainties are shown as yellowconcentric circles, each detected optical source within the 2- σ radius is highlighted by dashed yellow circles, and the cho-sen donor is indicated with bold red circles. In both Table A.2and Figure A.2, italicized SNRs are those classified usingour HR- L X criterion described in §2.4 (as opposed to thoseidentified directly in Long et al. 2014), italicized XRBs arethose associated with clusters, and classifications in paren- theses are objects with uncertain “candidate” classifications,as reported in Long et al. (2014) or as determined by ourmethods. 2.7. Assessing Misclassifications
While careful consideration is given to identifying LMXBsand HMXBs from each other and from non-XRBs, misclassi-fications are still possible. Here, we discuss possible sourcesof misclassification, our methods for mitigating these occur-rences, and the impact their inclusion could have on the finalXLFs.• A background AGN/quasar that is severely obscuredby an optically thick portion of M83 could mimic anX-ray source with no detectable optical counterpart(LMXB). This type of misclassification will prefer-entially affect the inner and disk regions in a rela-tively small area of the total coverage. We inspectthe color mosaic image and estimate the dust obscuredarea within which we cannot see background galax-ies to be roughly 20,000 arcsec . Scaling the detectedrate of 1,000 sources per square degree in the Chan-dra Deep Field down to similar flux levels as used here(Luo et al. 2017), we expect 1-2 background galaxiesto fall within these optically thick regions and hence bemisclassified as a LMXB. The number of backgroundgalaxies expected across the area covered by the fullmosaic (155,402 arcsec ) is 11-12; we identify 7. Oneof the galaxies in our sample (L19X178) is totally ob-scured. In all, our observations roughly match expec-tations. • Distant quasars appear as red, point sources in opticalimages and could be mistaken for a red giant donor starin a HMXB system. In fact, we identify 2 optical coun-terparts to X-ray point sources that we classify as can-didate quasars, based on their extended radial profilesand red colors. Overall, the space density of quasarson the sky is quite low, with only ∼ expected persquare degree with X-ray fluxes in our catalog. Thissuggests we should expect 1-2 quasars in our field ofview (155,402 arcsec ), consistent with our results.• A star in a dusty region can experience partial or to-tal extinction, resulting in a lower mass estimate. Po-tentially, this could lead to HMXBs misidentified asIMXBs, particularly those that are near the 8 M (cid:12) track. We addressed the possible effect of extinctionin §2.6.On the other hand, it is highly unlikely that a HMXBwould be misidentified as a LMXB based on extinc-tion in M83, because of the significant level required,which is not supported by a visual inspection of theoptical color images.• A high mass star may happen to lie coincident withan LMXB, causing the LMXB to be misidentified asan HMXB. Massive stars are rare compared to lowermass stars within galaxies and are highly concentrated,spatially, to regions of active star formation, such asthe spiral arms (as we find for M83 in §3). Simi-larly, XRBs themselves are uncommon. Statistical ar-guments therefore suggest that the chance superposi-tion of these two relatively rare phenomena is unlikely.As a final precaution, we compare our maps of theXRB populations to the stellar mass and SFR maps ofM83 published by L19. Since LMXBs and HMXBsare tracers of stellar mass and sSFR respectively, weexpect a correlation between the locations of thesepopulations and peaks in the stellar mass and sSFRmaps. We examine these in §3.• A parent cluster might be misidentified as a singledonor star, leading to an improper mass estimate usingits V − I color and V magnitude rather than the age ofthe cluster. We expect very few, if any, misclassifica-tions of this type, since clusters at the distance of M83are more extended than the PSF. To minimize mis-identifications, we cross-reference our sources with thepublished M83 cluster catalog published by Chandaret al. (2014).• An LMXB could have flared at the time of observa-tion, causing its disk luminosity and color to mimic that of a higher mass donor star. The probability ofthis occurring is statistically negligible, at the level of1 object per Milky Way stellar mass or so (well abovethe inferred stellar mass content of M83). The onlypersistent Milky Way analog is the black hole XRBGRS 1915+105. Less than a handful of other Galacticsystems, mainly long-period neutron stars, have com-parable luminosities, but the associated outburst dutycycles make them also statistically negligible.On the other hand, an LMXB that evolved from anIMXB progenitor may appear bright enough to be mis-taken for a higher-mass binary. We discuss this possi-bility at length in §5.1. X-RAY SOURCE SPATIAL DISTRIBUTIONSIn general, owing to the the short lifetimes of the donors,HMXBs trace regions of recent star formation, whereasLMXBs trace the integrated stellar mass content. Almostall previous works have taken a statistical approach to clas-sifying and studying populations of HMXBs and LMXBs,typically based on their location relative to different galac-tic structures (e.g., bulge, disk or outer region, as identifiedby, e.g., Mineo et al. 2012) or based on the SFR or stellarmass at their location (L19). However, there are dynamicalprocesses that can impart high space motions to XRBs, andthereby move them away from their sites of formation, andwe would not expect a perfect spatial correlation, in any case.This means that statistical and spatially-based classificationsare likely to have at least a few erroneous classifications ofindividual sources. In this Section, we study the locationsof HMXBs, IMXBs, and LMXBs based on our source-by-source classification method.Figure 5 shows the spatial distribution of each class ofXRB: HMXBs (blue squares), IMXBs (green crosses), andLMXBs (red points). We also find 7 AGN/quasars (orangeX’s). The classifications are over-plotted on three differentmaps of M83 constructed by L19 in Figure 6: stellar mass( M (cid:63) ; top), SFR (middle), and specific star formation rate(sSFR = SFR /M (cid:63) ; bottom). These maps show both a highstellar mass and a high SFR in the central region, higherSFRs in the spiral arms, and significantly higher sSFR in thearms compared to the inter-arm regions.In the central 0. (cid:48)
66 or 894 pc of M83, there are a total of 46XRBs; of these, 36 are HMXBs and 7 are LMXBs. This highfraction of HMXBs is perhaps not surprising, since M83 hasa central starburst. However, it is different than the centralregion of M101, which is strongly dominated by LMXBs,even though it is a later-type galaxy with a smaller bulge.Most HMXBs outside of the central region are found in re-gions of high sSFR. We find a few in ‘dark’ regions in themiddle and bottom panels of Figure 6; these may be sourceswith high space motions that have moved from their birth-
Figure 5.
Spatial distribution of LMXBs (red points), IMXBs(green crosses), and HMXBs (blue squares) in M83, as well as back-ground galaxies (orange X’s). Black outlines encircling the bulgeand inner disk regions at ∼ (cid:48)
66 and 3. (cid:48)
66 follow the prescriptionby Mineo et al. (2012), with the bulge radius from Dottori et al.(2008). sites. HMXBs also tend to be preferentially found in the spi-ral arms, with a fairly ‘clumpy,’ rather than even, distribution.LMXBs appear fairly centrally concentrated as expectedfrom an old spheroidal (bulge/halo) population. There are,however, sources distributed fairly evenly throughout M83,which may come from an old disk population. There are alsoa few LMXBs further away from the center and located inregions of high sSFR, i.e. where the SFR strongly dominatesover the stellar mass. We checked the local background inthese regions; extinction appears to be lower than closer tothe center of M83, and the background level is sufficientlylow that we would easily be able to detect donor stars downto 3 M (cid:12) . These sources would be misclassified as HMXBsin studies that use a spatial approach, since they fall within aregion of high sSFR (L19) and also within the ‘disk’ region,as defined by Mineo et al. (2012), typically believed to bedominated by HMXBs. Overall, the spatial distribution ofthe XRB population is fairly mixed: whereas HMXBs and(to a much lesser extent) IMXBs seem to track higher SFRregions than LMXBs, LMXBs can be found in the bulge aswell as the outer disk, and the bulge itself is home to a largeHMXB population. X-RAY LUMINOSITY FUNCTIONSA key goal of characterizing the XLF(s) of XRBs is to as-certain whether a statistically significant downturn exists athigh luminosities. Theoretically, such a “cutoff” is expectednear the Eddington luminosity for stellar-mass compact ob-jects, but observations have yet to confirm this predictionwith high confidence. Assessing the presence and robust-ness of such a downturn is inherently dependent upon thechosen functional shape of the XLFs. Virtually all investi-
Stellar Mass (a)Star Formation Rate (b)Specific Star Formation Rate (c)
Figure 6.
Overlays of LMXBs (red points), IMXBs (green crosses),HMXBs (blue squares), and background galaxies (orange X’s) ontothe (a) stellar mass, (b) star formation rate, and (c) specific star for-mation rate maps for M83 generated by L19. All three maps areshown with a linear color scale. (cid:39) at low luminosi-ties, gradually steepens above (cid:96) = 37 . − . and has arather abrupt cut-off at (cid:96) = 39 . − . .” In later works, thebest-fit values of the break and cutoff luminosities fall near (cid:96) (cid:39) and (cid:96) (cid:39) , respectively (e.g., Mineo et al. 2012,L19). However, the lack of a unified approach (e.g., fittingcumulative vs. differential and/or binned vs un-binned distri-butions; fixing vs. fitting for the cutoff luminosity) makes itsomewhat difficult to compare results across different stud-ies. Furthermore, whether the presence of a break and/or acutoff in the XLFs is required by the data with high statisti-cal confidence remains an open, key question, whose answeris again intertwined with the choice of the XFL functionalshape.As shown by Mok et al. (2019) in their thorough explo-ration of the mass function of young star clusters (see alsoC20, and references therein), methods that bin the differen-tial distribution in luminosity (or mass) intervals result in sta-ble fits for the power-law indices, while fits to the un-binneddistributions give the most robust detection of any downturnat higher luminosities.Guided by the above considerations, we approximate theshape of the XLF for XRBs in M83 with two functionalshapes: a single PL, and a Schechter function (Schechter1976). We fit the X-ray luminosity distribution of the (a)composite sample (i.e., all XRBs), as well as (b) HMXBs,(c) IMXBs, and (d) LMXBs, separately. Whereas the com-pact source fluxes were originally extracted over the 0.5-7keV energy range, for the purpose of XLF fitting, L19 con-verts the source fluxes to a 0.5-8 keV range, as appropriate,i.e. using either a template spectral shape or the actual sourcespectrum, depending on the number of counts. This wasmeant to facilitate a comparison with the literature; we ad-here to the same choice in this Paper.To assess the presence of a truncation – here defined asa luminosity above which no sources exist – we adapt the methodology developed by Rosolowsky (2005) to investigatethe shape of the mass function of giant molecular clouds. Toaccount for the presence of a maximum luminosity value ( L c )in the distribution, we approximate the cumulative distribu-tion as: N ( > L ) = N C (cid:34)(cid:18) LL c (cid:19) β +1 − (cid:35) , (1)where N C is the number of XRBs more luminous than / ( β +1) L c , at which point the distribution shows a signif-icant deviation from a single power law of index ( β + 1) .In the case where N (cid:39) , there is no significant deviation,and the distribution is consistent with sampling from a singlepower law. With this formalism, the cumulative mass distri-bution below L c is proportional to ( L/L c ) β .The differential Schechter luminosity distribution is pro-portional to ( L/L (cid:63) ) , where L (cid:63) — known as the Schechter“knee” — corresponds to a characteristic luminosity abovewhich the distribution declines exponentially, as follows: dNdL = N (cid:63) (cid:18) LL (cid:63) (cid:19) β exp − ( L/L (cid:63) ) , (2)where N (cid:63) Γ(1 + β, is the number of galaxies with L > L (cid:63) ,and Γ( − b, y ) is the incomplete gamma function. This well-known functional shape provides a good analytical approxi-mation to the measured luminosity (and/or mass) distributionof astronomical objects across a wide dynamic range.We examine the shape of M83’s XLFs with three methods:(i) We perform a single PL fit to the differential luminositydistributions, binned in intervals with an equal numberof sources. This method yields the most stable and ro-bust constraints to the power-law index of the distribu-tion (Mok et al. 2019).(ii) We utilize the IDL script MSPECFIT (Rosolowsky2005) to fit a single PL — with and without trunca-tion — to the un-binned, cumulative luminosity distri-butions. This method is sensitive to the presence of adownturn at high luminosities, i.e., it serves to identifya characteristic luminosity above which the distributiondeclines sharply (if any).(iii) We perform a Maximum Likelihood (ML) fit with aSchechter function to the un-binned differential lumi-nosity distributions, following Mok et al. (2019). Thismethod does not use binned data (which can hide weakfeatures at the ends of the distribution), nor cumulativedistributions (where the data points are not independentof one another). It thus gives the most robust test forthe presence of a statistically significant exponential de-cline at high luminosities.1The top, middle and bottom panels of Figure 7 illustratethe results of method (i), (ii), and (iii), respectively. Unlessotherwise noted, fits are performed above the 90% complete-ness limit of (cid:96) = 36 . identified by L19.Fitting the differential XLF of M83 (composite sample)with method (i), using bins by 10 sources each, yieldsa slope of − β = 1 . ± . . The inferred slopes forthe HMXB, IMXB, and LMXB XLFs are, respectively − β = 1 . ± . , . ± . , and . ± . , sug-gesting that the HMXBs are characterized by a somewhatshallower overall distribution (top panels of Figure 7; adopt-ing bins of , and sources yields consistent results, withinthe uncertainties).With respect to the presence of a break, method (ii) and(iii) give consistent – and interesting – results. Fits to thecumulative XLF with a truncated power law (TPL), with MSPECFIT , indicate that the HMXB XLF is the only dis-tribution that shows any statistically significant evidence, atthe ∼ σ level, for a high-energy cutoff (this is indicated byvalues of the N c parameter in excess of unity in the middlepanels of Figure 7).The ML fits with a Schechter function confirm this trend.The bottom panels in Figure 7 show the 1-, 2-, and 3- σ con-fidence contours for the best-fit values of the Schechter slopeand knee luminosity. The best-fit values are indicated bythe dashed black lines (the upper limit to the knee luminos-ity was set to be 100 times higher than that of the brightestXRB in each sample, ensuring convergence in all cases). Aformally statistically significant detection of the exponentialcutoff would be seen as closed 3- σ contours in these dia-grams. We find only marginally significant evidence (at the1- to 2- σ level) for an exponential cutoff at the bright end ofthe composite XLF, suggesting that M83’s XLF is formallyconsistent with the expectations of sampling statistics froma single power-law. This is true for the composite XLF aswell as individual donor classes. Interestingly though, inline with the conclusions from method (ii), the presence ofa (marginally significant) exponential cutoff appears to bedriven by the HMXB population, which exhibits a knee at (cid:96) = 38 . +0 . − . (at the 1- to 2- σ level), whereas the LMXBand IMXB XLFs show no evidence for a statistically signifi-cant dive (as indicated by the open 1- σ contours in the thirdand fourth plots of the bottom panel of Figure 7).In summary, we find that, when approximated by a sin-gle PL, the composite XRB XLF of M83 has an index of − . ± . ; the shapes of the XLFs for the HMXB,LMXB, and IMXB populations show marginal deviations,with HMXBs having a shallower slope than both LMXBsand IMXBs. Our maximum likelihood fits to the Schechterfunction do not find formally statistically significant evidence for an exponential cutoff at the bright end of the luminosityfunctions. However, the presence of a high-energy cutoff inthe HMXB XLF above (cid:96) = 38 (at the ∼ σ level) is indi-cated by both the ML and cumulative XLF fits.In §5.2, we compare our fit results for the XLFs of differ-ent populations in M83 with those from previously publishedresults for M83, as well as average XLFs derived from largesamples of (star forming) galaxies. DISCUSSION5.1.
The Nature of Donor Stars in IMXBs and HMXBs
The majority (184 out of 214) of M83’s XRBs have can-didate donors that we classified as either intermediate (3-8 M (cid:12) ) or high-mass ( > M (cid:12) ) stars based on the evolutionarytracks in Figure 4. A few detected donors fall beneath the 3 M (cid:12) threshold and are considered LMXBs.Interestingly, we find that the majority of the intermediate-and high-mass donor stars do not follow the blue main se-quence ridge that runs along the left side of the models, butrather occupy the redder portion of the evolutionary tracks.While this is likely due to a combination of effects, the ma-jority of these objects are likely truly evolved stars. To startwith, HMXBs are typically wind-fed (as opposed to disk-fedas a result of the donor filling its Roche lobe): the brightest ofthese will be those objects with more evolved donors, leadingto lower surface gravity and thus higher wind loss rates.Indeed, the brightest, persistent HMXBs in the Milky Way(MW) and Magellanic Clouds (Grimm et al. 2003) have ei-ther evolved or peculiar main sequence donor stars; these in-clude, e.g., a blue supergiant in Cygnus X-1 (MW); a (high-extinction) Wolf-Rayet star in Cygnus X-3 (MW); a blue su-pergiant in GX 301-2 (MW); a blue supergiant in SMC X-1; amain sequence B stars with highly distorted shape in LMC X-1; and an evolved O star in LMC X-3 (Liu et al. 2006). Gen-erally speaking, about 60% of the MW HMXBs are known orsuspected Be/XRBs, while 32% are supergiant/X-ray bina-ries (Liu et al. 2006). Whereas Be/XRBs in very blue bandsmay be expected to be close to the main sequence, their de-cretion disks are extremely red, and can move the overallcolor off of the main sequence. At the same time, since brightBe/XRBs are predominantly transients rather than persistent,they are less likely to be represented in our investigation withrespect to truly evolved stars.The right panel of Figure 4 shows a comparison of M83’sdetected donors (in black), with all of the X-ray bright MWXRBs listed in the Liu et al. (2006) and Liu et al. (2007) cat-alogues (blue points for HMXBs, red for LMXBs) for which Brighter than 0.2 µ Jy in the 2-10 keV range, as measured by the
Rossi X-ray Timing Explorer ; this corresponds to roughly (cid:96) (cid:39) erg s − at thedistance of M83. Method (i)Method (ii)Method (iii)
Figure 7.
Method (i): Fits to the differential XLFs, binned in intervals of N = 10 sources per bin (following Mok et al. 2019).Method (ii): Fits to the cumulative, un-binned XLFs with a single power law (PL) and a truncated power law (TPL; Rosolowsky 2005). For thetop and middle panels, the dashed black vertical line indicates the 90% completeness limit of (cid:96) = 36 . , above which the fits are performed.Method (iii): Maximum Likelihood fits to the cumulative XLF with a Schechter function, following Mok et al. (2019). The dashed black linesindicate the best fit values for the slope and knee luminosity. Contours refer to the 1-, 2- and 3- σ confidence levels. The green triangles indicatethe luminosity of the brightest object within each sample; if the best fit knee luminosity is greater than the maximum luminosity probed by thesample, the presence of an exponential downturn is not significant. measured B and V magnitudes are available. Apparent mag-nitudes were converted to absolute values using the formula M = m + 5 − A V − d , where d is the distance of thesource in pc and A V is the interstellar extinction given byLiu et al. (2006) and Liu et al. (2007). The distance to eachsource was approximated by the relation A V ≈ r mag forsources with a galactic latitude b < ◦ , where r is the dis-tance in kpc. It is reassuring that, even based on this cur-sory conversion, the division between HMXBs and LMXBsamong MW objects aligns nicely with the expected V mag- nitude of LMXBs as we have defined it for M83. We stressthat, by construction, these are intrinsically blue systems, forwhich extinction within the Galactic disk does not prevent adetection in the optical. As a result, the lack of Galactic sys-tems red-ward of B-V (cid:39) . in Figure 4 is largely a selectioneffect.At the same time, the large color spread for the M83 sys-tems is likely compounded by intense X-ray irradiation andevolutionary effects. Specifically, a non-negligible fractionof the systems that we classify as IMXBs are likely abnor-3mally luminous LMXBs. The initial IMXB formation ratedepends on the star formation history of the host galaxy.Given that M83 has been forming stars at a fairly constantrate over at least the last several 100 Myr, one would ex-pect a non-negligible initial contribution from intermediate-mass stars (and thus IMXBs) to the total population; in fact,the probability of forming an XRB with an initial donor be-tween 1.5-4 M (cid:12) is estimated to be > ∼ times higher that of a < ∼ . M (cid:12) donor (Pfahl et al. 2003). At the same time, how-ever, population synthesis models show that for neutron staraccretors (which comprise the majority of the population),intermediate-mass donors quickly evolve into low-mass starsthrough a short-lived thermal mass transfer phase (Podsiad-lowski et al. 2002; Pfahl et al. 2003). This yields a populationof abnormally hot and luminous LMXBs, with IMXB pro-genitors, that may be misclassified as IMXBs through ouroptical method (a MW analog is the donor in the LMXBCygnus X-2, which has a dynamical mass of 2 M (cid:12) in spiteof being far too luminous and hot for a low-mass sub-giantPodsiadlowski & Rappaport 2000).That a fraction of the donors which we identify asintermediate-mass may in fact be low-mass is also con-sistent with their spatial distribution (green crosses in Figure5), as they do not seem to trace the spiral arms as well as theHMXBs (blue squares); this can be expected of systems thatare longer-lived than a typical Galactic revolution time-scaleof ∼
250 Myr.To summarize, for M83 we conclude that (i) the published,X-ray based XLFs suffer from massive contamination fromSNRs; (ii) our method confirms a non-negligible contributionfrom low- and possibly intermediate-mass XRBs to the totalXRB XLF, i.e. between 20 and 50%, in broad agreementwith X-ray based XLFs (30%).5.2.
Comparison With X-ray based XLFs
In this section, we compare our results first with those ofL19 (§5.2.1) and older works (§5.2.2).In general, caution must be exercised when making di-rect comparisons with the published XLFs, for a numberof reasons. First, our optical CMD-based approach enablesus to directly differentiate between different classes of XRBdonors. In contrast, purely X-ray data-based XLF investiga-tions indirectly differentiate between HMXBs and LMXBsby positing that the former population scales with star for-mation rate, and the latter with stellar mass. Furthermore,X-ray based studies do not explicitly differentiate betweenintermediate- vs. low- or high-mass XRB donors at all.Rather, the assumption is made that the SFR-tracing XRBpopulation maps into truly high-mass donors ( > ∼ M (cid:12) ). Inturn, this hinges on the assumption that the adopted SFRtracer is sensitive to truly instantaneous (and by extension very short-lived) star formation episodes. Our optical recon-naissance XRB classification enables us, for the first time, totest this assumption. Since previous works have classified allXRBs into only high- or low-mass, it is not clear where thesources we classify as IMXBs end up in those studies. In par-ticular we compare whether the inferred number of objects ineach category agree with the expectations from the publishedXLFs, where HMXBs are allegedly truly high-mass donors.Additionally, with the exception of L19, all prior X-raybased investigations of high- vs. low-mass XRB XLFs relyon the assumption of little or no contamination to the com-pact X-ray population other than from cosmic backgroundsources, which is typically minimized by limiting the searchradius. While this is well justified in some cases (e.g., formassive elliptical galaxies, which are naturally devoid ofHMXBs), it is not necessarily valid for cases such as starforming spirals, where a non-negligible fraction of the diskXRBs are likely LMXBs, particularly in mildly star form-ing galaxies. Although the contamination from X-ray emit-ting SNRs has also been historically neglected, independentstudies (Long et al. 2014) show that those represent a majorsource of contamination to the compact X-ray source popula-tion of M83 (this might apply to actively star-forming galax-ies in general). 5.2.1. Comparison with L19
The most recent and detailed analysis of XRB XLFs todate is presented by L19: they consider a sample of 38nearby galaxies (including M83) spanning a vast range ofmorphologies and sSFRs. They use spatially resolved SFRand M (cid:63) maps to divide the ( ∼ Chandra -detected X-ray sources into sSFR bins and derive a global model forthe scaling of the HMXB XLF with SFR and of the LMXBXLF with M (cid:63) (accounting for the cosmic background X-raysources with a model that scales with sky area). In addition,they present ‘standard’ XLF fits for each of the target galax-ies; these are computed following a forward-fitting approachwhere the XRB and cosmic X-ray background source con-tributions are fit for simultaneously and convolved with acompleteness function for each galaxy. For each galaxy, theXRB contribution to the (differential) XLFs is modeled as ei-ther a single or a broken PL (see equations 4 and 5 in L19 forthe adopted functional shapes). For practical purposes, thebreak and high-energy cutoff luminosity for the individualgalaxy fits are fixed to (cid:96) b = 38 . and (cid:96) c = 40 . , respec-tively. A detailed comparison to those results, includingbroken power-law fits, is presented in the Appendix. Here,we focus on the broad picture, and particularly on whetherthere are any high-level discrepancies.For M83, L19 reports a power-law index of − . +0 . − . forthe single PL fit to the composite XLF. This value is slightly4steeper than the value we infer from our preferred method (i; − β = 1 . ± . ), as well as our method (ii; − β = 1 . ± . ). We suspect that the reason for this mild discrepancyhas to do with the issue of SNR contamination, which wefurther discuss below.Perhaps more interesting is to assess whether the XLF isbest described by a single PL or exhibits any evidence fora statistically significant deviation from it (in the form or abreak, downturn, or cutoff). L19 concludes that, with theexception of one target, a single PL provides a statisticallyacceptable fit to the data of all 38 galaxies under examina-tion, including M83. They note that, while broken powerlaw fits typically provide improvements to the fit statistics,in very few cases are those improvements statistically signif-icant. This is qualitatively consistent with our results, wherethe composite XLF of M83 is consistent with being sampledfrom a single power law, with only marginal evidence for a(HMXB-driven) downturn.Next, we compare the results we obtained for the HMXB,LMXB, and IMXB populations in M83 with the globalHMXB and LMXB XLFs derived by L19 . Starting withthe indices, the L19 HMXB XLF has a best-fit slope of − . ± . . For the LMXB XLF, the best-fit model isa broken PL with indices − . +0 . − . and − . +0 . − . , re-spectively, below and above a break luminosity of (cid:96) b =38 . +0 . − . .Our fit to the HMXB XLF of M83 with a single PLmodel, with method (i), yields a shallower index, with β = − . ± . . In terms of preferred functional shape, as dis-cussed in §4, the cumulative XLF fit shows evidence (at the ∼ σ level) for a downturn in the HMXB population, at (cid:96) = 38 . ± . . This is confirmed by the ML fits with aSchechter function, which also find marginal evidence, at the1- to 2- σ level, for an exponential decline of the HMXB XLFat (cid:96) (cid:39) . +0 . − . .A key finding in L19 indicates that the composite HMXBXLF has a more complex shape than previously reported; itexhibits a rapid decline between L X (cid:39) − erg s − , a‘bump’ between − erg s − , and an approximatelyexponential decline above erg s − . We do not see thislevel of complexity for the XLF of HMXBs in M83. Simi-larly, our analysis does not indicate any significant deviationfrom a single PL for the LMXB XLF in M83, albeit this mayagain be due to low number statistics. A direct comparisonwith L19 using a broken power-law approximation of the For the purpose of this comparison, we refer to the best-fitting parame-ters from their “Cleaned Sample” (which excludes from the sample fivegalaxies with low metallicity and three others with high specific number ofglobular clusters).
XLF is made in the Appendix.Some of the above discrepancies, such as the steeper slopeobtained by L19 when fitting M83’s total XLF, are likelydriven by the high degree of SNR contamination to the M83’sX-ray source population (Long et al. 2014; this is less likelyto affect our conclusions regarding the presence of a down-turn, since all the sources we classified as SNRs are fainterthan (cid:96) = 37 . ). As detailed in §2.4, based on the dedicatedstudy by Long et al. (2014), we classified 103 of M83’s X-ray sources as SNRs; 77 out of those 103 are brighter thanthe 90% completeness limit of (cid:96) = 36 . , above which all fitsare performed. While a detailed analysis of how this affectsthe measured XLF slopes for each XRB group is deferredto the Appendix, here we focus on comparing the number of sources that we classify as HMXBs, LMXBs and IMXBsagainst the expectations from the global HMXB and LMXBXLFs obtained by L19 .Starting with HMXBs, L19 quote a normalization value K HMXB = 2 . +0 . − . per M (cid:12) yr − at (cid:96) = 38 . By convolv-ing the HST footprint (155,403 arcsec ) with M83’s star for-mation rate map (Figure 6b), we estimate an enclosed SFR of2.28 M (cid:12) yr − . Adopting this value, M83 is then expected tohave (cid:39) HMXBs with (cid:96) ≥ . . This is to be comparedwith the 63 HMXBs identified by our optical reconnaissanceanalysis above the 90% completeness limit of (cid:96) = 36 . . Ifwe also consider those X-ray sources that were rejected asSNRs based on the cuts made in §2.4, we obtain a total of109 objects, in good agreement with the expectations fromL19.For LMXBs, we estimate that the HST footprint encloses . × M (cid:12) in stellar mass. With a LMXB XLF nor-malization value K LMXB = 26 . +3 , − . per M (cid:12) , the L19XLF predicts (cid:39)
48 LMXBs above (cid:96) ≥ . . We classify23 sources as LMXBs above (cid:96) ≥ . (or 30 with the in-clusion of 7 X-ray sources that we rejected as SNRs). Ad-ditionally, we identify 34 IMXBs above (cid:96) ≥ . (58 if theSNRs are included). While the absolute numbers are lessimportant (the global XLFs by L19 have a scatter of 0.4dex; we include a few sources that are located outside ofthe SFR and stellar mass maps generated by L19; addition-ally, we may be too aggressive in rejecting candidate SNRs),this exercise shows that, for a galaxy with the mass and SFRof M83, based on state-of-the-art X-ray based XLF models,about 30% of the detected XRBs ought to be LMXBs. Af-ter correcting for SNR contamination, we estimate that about20% (23/120) of the XRBs above our completeness thresh-old are low-mass, whereas an additional ∼
30% (34/120) are For this purpose, we adopt their best-fit values for the Cleaned sample andmultiply the expected number of sources by the constant scaling factor ω =0 . , inferred by L19 specifically for M83. Comparison With Older Works
In this section, we compare our results for HMXBs withthose from Mineo et al. (2012) and Sazonov & Khabibullin(2017). We defer a comparison with Zhang et al. (2012) forLMXBs to the Appendix, where a similar broken power-lawfitting methodology as used is presented. Additional com-parisons between the results detailed in L19 and those fromMineo et al. (2012) and Zhang et al. (2012) are found in L19.Mineo et al. (2012) built on the seminar works by Gil-fanov (2004) and Grimm et al. (2003), which all rely onthe assumption that HMXB in star-forming galaxies can beidentified by their location outside of the central bulge region,but sufficiently close that contamination by the cosmic back-ground is not significant. They create a composite XLF forHMXBs based on sources detected in Chandra observationsof 29 nearby star-forming galaxies (including M83). Theymake no further correction for SNR, background galaxies,or LMXBs, beyond spatial cuts. For their presumed HMXBXLF, they find a power-law index of β = − . ± . ,with a normalization K HMXB = 2 . ± . per M (cid:12) yr − .Their XLF predicts (cid:39) HMXBs above our complete-ness limit and for the estimated enclosed SFR of M83 (2.28 M (cid:12) yr − ). For M83, we find β = − . ± . (methodi) and β = − . ± . (method ii), statistically shallowerthan Mineo et al. (2012), with 63 HMXBs above the 90%completeness limit. However, if we include the SNRs thatwere discarded from our catalog, there are 109 candidateHMXBs, which is in good agreement with the number pre-dicted from their fits. The inclusion of SNRs also steepensour power-law fits, since SNRs tend to have fainter luminosi-ties (see §2.4). These results indicate that at least some ofthe difference between our results and those found by Mineoet al. (2012) are driven by SNRs.More recently, Sazonov & Khabibullin (2017) focused onthe bright end of the XLF ( L X > erg s − ) for a sam-ple of 27 nearby, star-forming galaxies. There are a numberof fundamental differences in the observations and approach,which make direct comparisons challenging. The study in-cludes energies down to 0.25 keV, which introduces a num-ber of super-soft sources that are unlikely to be detected inour work, that of L19, or of Mineo et al. (2012). Another keydifference is that they fit each X-ray spectrum to determine itsunabsorbed, rather than observed, luminosity. They identify (and eliminate) a handful of foreground stars and backgroundgalaxies based on visual inspection of optical counterparts,and statistically correct for LMXB contamination by usingthe scaling relation from Gilfanov (2004). Like other works,no correction is made for SNRs.Despite these differences, the Sazonov & Khabibullin(2017) XLF has a best fit power-law index of β = − . ± . , very similar to that found by L19 and Mi-neo et al. (2012). Their scaling, however, is significantlyhigher — almost certainly due to the inclusion of a numberof super-soft X-ray sources which are not found in the obser-vations used to build our sample; an open question remainsthe possible overlap of systems that are classified as super-soft and the X-ray emitting SNRs identified by Long et al.(2014). SUMMARY AND CONCLUSIONSBuilding on the methodology developed by C20 for M101,we carry out an optical reconnaissance study of the XRBpopulation in the nearby, star forming spiral galaxy M83.This method allows us to directly characterize the donor starsof each
Chandra -detected compact X-ray source as low-, vs.intermediate- vs. high-mass stars (here defined as < ∼ M (cid:12) , − M (cid:12) , and > ∼ M (cid:12) , respectively) by comparing theirdonor stars to stellar evolutionary models or by estimatingthe ages of their parent clusters using optical photometryfrom multi-band high-resolution HST imaging, while alsoenabling a direct identification of background contaminants.Similar to what was found by C20 for M101, we show thathigh-quality HST imaging of the star forming spiral M83 en-ables the direct detection of an optical counterpart down toabout 3 M (cid:12) .After accounting for SNR contamination (which is espe-cially severe in the case of M83), the differential XRB XLFof M83’s (between 0.5-8 keV) is best fit by a single powerlaw with slope − β = 1 . ± . . At variance with previousstudies, we also explore a Schechter function as a physicallymotivated alternative to the cutoff and/or broken power lawsthat are typically adopted to approximate XRB XLFs. OurSchechter modeling (the results of which are illustrated inthe bottom panel of Figure 7) only identifies a marginallysignificant (at the 1- to 2- σ level) exponential downturn forthe HMXBs XLF in M83, (cid:96) (cid:39) . +0 . − . . In contrast, theLMXB and IMXB distributions, as well as the total XLF,are formally consistent with sampling statistics from a singlepower-law.That the HMXB XLF in M83 deviates somewhat from asingle power-law is confirmed by our cumulative distributionanalysis, for which we adopt a formalism that was developedfor the mass function of giant molecular clouds (Rosolowsky2005). Through this method, we identify a marginally sig-nificant truncation at (cid:96) = 38 . ± . , at the 2.5- σ level.6Again, we find that no deviations from a single power-laware required for either the LMXB or IMXB population.Last, our optical reconnaissance methodology enables us,for the first time, to make direct inferences on the role ofIMXBs in the XRB XLFs. The assumption that the SFR-tracing XRB population maps into truly high-mass donors istypically predicated upon the notion that the adopted SFRtracer is sensitive to instantaneous, and hence very-shortlived, star formation episodes. However, we note that the sur-vival rate of IMXBs is arguably dependent on the host galaxystar formation history . For spiral galaxies like M83, whichhad fairly constant (high) rates of star formation over at leastthe last Gyr (Chandar et al. 2010), IMXBs are likely to yielda non-negligible contribution to the XRB population. At thesame time, X-ray binary evolutionary models show that, af-ter sustaining a highly super-Eddington mass loss phase onthermal time scales, these will quickly evolve into low-massdonors with unusually hot spectral types. Owing to this ef-fect, we estimate a non-negligible contribution from low- and possibly intermediate-mass XRBs to the global XLF of thestar-forming galaxy M83, i.e. between 20 and 50% (to becompared with an estimated contribution from LMXBs atthe 30 per cent level based on the L19 X-ray XLFs). Fi-nally, we caution against a sizable contribution from X-rayemitting SNRs to the published XLFs for M83, and possiblyother star-forming galaxies (for the case of M83, more than30% of the compact X-ray sources that fall within the HSTfootprint have been identified by Long et al. 2014 as SNRs).In future papers, we will extend our methodology to a sam-ple of several tens of nearby galaxies with high-quality HSTand Chandra coverage, so as to increase our number statis-tics and deliver a direct census of the XRB population basedon our novel optical reconnaissance of the donor type.ACKNOWLEDGMENTSQH is partially funded by a Rackham Merit Fellowship,awarded by the University of Michigan Rackham GraduateSchool. We are grateful to Tom Maccarone for useful com-ments and suggestions.REFERENCES
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J. 1974, MNRAS, 167, 13Zhang, Z. Gilfanov, M., & Bogd´an, ´A. 2012, A&A, 546, A36Zhang, Z., Gilfanov, M., Voss, R., et al. 2011, A&A, 533, A33 A. SINGLE VS. BROKEN POWER-LAW FITSTo facilitate a direct comparison with the literature, where the XRB XLFs are typically fit with single or broken power-laws(PLs and BPLs), here we approximate M83’s XRB luminosity distribution as follows: N ( > L ) PL = κ PL L − ( α − (A1) N ( > L ) BPL = (cid:40) κ BP1 L − ( α − , ( L ≤ L b ) κ BP2 L − ( α − , ( L > L b ) (A2)where N ( > L ) is the cumulative XLF, L b is the break luminosity of the broken power-law (BPL), and the κ values are normaliza-tion constants (note, κ is defined differently than the normalization constants of the differential XLF fits, K, discussed in §5). Allluminosities are in units log erg s − . We choose to fit un-binned cumulative distributions here, as they tend to be more sensitiveto the presence of a downturn at high luminosities. At the same time, the choice to represent the power-law indices as ( α − ) ismeant to facilitate a direct comparison to those studies that adopt a differential, rather than cumulative, form of the XLF. Apartfrom the break luminosity, which is fixed to (cid:96) b = 38 . for consistency with L19, all variables are fitted for, using the Python scipy.curve fit function. We are primarily interested in comparing our fits to the results reported by L19. However, sinceprevious studies do not take into account the SNR contamination to the compact X-ray source population, we also examine theeffects of removing (secure and candidate) SNRs to the shape of the XLF. For completeness, we also report the results of fittingthe HMXB, LMXB, and IMXB samples separately. Table A.1 and Figure A.1 summarize the results of our fits.Our “Fiducial Sample” (from the main Paper, sample a) includes a total of 120 sources above the 90% completeness limit of (cid:96) = 36 . . This excludes 103 sources identified as SNRs either by Long et al. (2014, 76 in total) or by their X-ray properties (27additional sources), as described in §2.4. For this sample, we find a PL index of . ± . , and BPL indices of . ± . and . ± . , respectively below and above the break. This is to be compared with the values inferred by L19: a PL index of . +0 . − . , and BPL indices of . +0 . − . and . +0 . − . below and above the break, all of which are formally consistent with ourbest-fit values, within the uncertainties.Including the SNRs to the sample (“With SNRs”, sample b) yields a single PL index . ± . , whereas the BPL indices are . ± . and . ± . . Not surprisingly, the inclusion of these (low-luminosity) sources slightly steepens the inferred PLslope, as well as the BPL slope below the break. The X-ray based diagnostics we developed to identify and reject SNR candidates(see §2.4) may be too aggressive in that it may lead to the rejection of faint, X-ray soft XRBs. To fully illustrate the effects of ourrejection criteria, we present the results of our fits to a sample in which only the 76 X-ray sources that were directly identified byLong et al. (2014) are removed (“With spec. SNRs”, sample c), while the additional 27 SNR candidates that we reject from thefiducial sample on the basis of the X-ray color are included in the XLF. However, it should be noted that, in terms of the inferredslopes, all three fits are consistent with the values reported by L19, within 2- σ . This suggests that, though strict, our SNR filteringmethod does not drastically alter the overall shape of the XLF. It does, however, alter the normalization.For completeness, we compare our BPL fits to Zhang et al. (2012), which studies the LMXB XLF using a sample of 20 nearbyelliptical galaxies. A comparison to this study is also conducted in L19. They fit the XLF to a BPL model with two breaks (at . × and × erg s − ), as opposed to a single break used both by L19. L19 find no improvement in the quality of thefit when adopting two breaks; therefore, they focus only on the parameters around the first break, a prescription we follow here.The indices of the LMXB XLF found by Zhang et al. (2012) are . +0 . − . and . +0 . − . , which yields ∼ expected LMXBswithin the HST footprint of M83. By our methods, we find 23 LMXBs in our fiducial sample (a), 30 LMXBs in sample (b),and 26 LMXBs in sample (c). Like other studies that indirectly estimate the contribution of LMXBs in late-type galaxies, theZhang et al. (2012) XLF most likely includes SNR contamination, as well as contamination from IMXBs. Like L19, we obtainslopes that are steeper in the faint end by a statistically significant margin for all fits. At higher luminosities, however, ratherthan steepening, our LMXB XLF becomes much shallower. There are two possible explanations for these observations: first,this may be due to the fact that M83 is a late-type galaxy, and at higher sSFRs, young LMXBs may achieve higher luminosities(Fragos et al. 2013; Kim & Fabbiano 2010; Lehmer et al. 2014, 2017; L19); or second, a BPL is simply a poor representation ofthe LMXB XLF, as demonstrated in §4.9 Figure A.1.
Single and broken power-law function fits to the composite XRB XLFs in M83 (i.e., the “All XRBs” rows) of the fiducial samplecontaining all XRBs with luminosities above the 90% completeness limit (left), sources including XRBs and all SNR (center), and sources withonly SNRs identified in Long et al. (2014) removed (right). See Table A.1 for the corresponding best-fit parameters.
Table A.1.
XRB XLF fit parameters P OWER L AW B ROKEN P OWER L AW † XLF κ PL α κ BP1 κ BP2 α α (1) (2) (3) (4) (5) (6) (7) (a) Fiducial Sample All XRBs 60.89 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± (b) With SNRs All XRBs 64.71 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± (c) With Spec. SNRs All XRBs 62.01 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± OTE —The best-fit parameters inferred by approximating the XLFs with the functional shapes given in Equations A1 and A2. † For the broken power-law fits,the break luminosity is fixed at (cid:96) b = 38 , to facilitate comparison with Lehmer et al. (2019). Three subsamples are examined: (a) the fiducial sample of XRBsidentified in the main Paper; (b) the fiducial sample plus all SNRs; and (c) the fiducial sample plus only
SNRs identified in §2.4 using our L X -HR criterion,with all SNRs identified in Long et al. (2014) removed.Columns (1)-(10) describe:(1) the population of XRBs fit by each function; (2) the normalization of the power-law; (3) the index of the power-law;(4) the normalization of the power-law fit to the XLF below (cid:96) b ; (5) the normalization of the power-law fit to the XLF above (cid:96) b ;(6) the index of the power-law fit to the XLF below (cid:96) b ; (7) the index of the power-law fit to the XLF above (cid:96) b . Table A.2 . Properties and Classifications of M83 X-ray Sources
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X048 2CXO J133648.3-295244 X046 204.201273 -29.879037 36.4 -7.180338 -0.119078 0.196804 SNR — 2.0L19X049 2CXO J133648.2-295136 X047 204.201358 -29.860496 36.0 -2.488338 2.202922 1.067804 IMXB — 2.0L19X050 2CXO J133648.7-295229 X048 204.203291 -29.874848 37.1 -6.195338 -0.051078 0.157804 HMXB — 1.0L19X051 2CXO J133649.1-295258 X049 204.204673 -29.882838 37.6 -5.178338 0.190922 0.666804 HMXB — 3.0L19X052 2CXO J133649.1-295125 X050 204.204964 -29.856996 36.3 — — — LMXB — 1.0L19X053 2CXO J133649.2-295303 X051 204.205104 -29.884200 37.5 -3.026338 -0.191078 0.429804
SNR — 2.0L19X055 2CXO J133649.4-295014 X052 204.205935 -29.837387 36.7 -3.747338 0.325922 0.184804 IMXB — 1.0L19X056 2CXO J133649.7-295217 X053 204.207525 -29.871477 37.0 -3.664338 -0.396078 -0.012196 SNR — 1.0L19X057 2CXO J133649.9-295513 X055 204.208121 -29.920346 37.0 — — — LMXB — 1.0L19X058 2CXO J133649.9-295259 X054 204.208128 -29.883216 36.8 -4.758338 0.882922 1.579804
LMXB
SNR — 2.0L19X061 None None 204.209423 -29.876018 36.4 -1.899338 1.443922 1.435804 IMXB — 1.0L19X062 2CXO J133650.5-295304 X061 204.210805 -29.884544 36.2 -3.148338 0.787922 2.619804 SNR — 1.0L19X064 None None 204.211391 -29.870654 36.0 -5.164338 1.749922 1.994804 HMXB — 2.0L19X065 2CXO J133650.7-295041 None 204.211619 -29.844965 36.0 -5.074338 0.749922 1.030804 HMXB — 1.0L19X066 2CXO J133650.8-295240 X063 204.212054 -29.877772 36.7 -6.060338 0.314922 1.270804 SNR — 1.0L19X067 None X064 204.212369 -29.883312 36.5 -5.145338 -0.245078 -0.000196 (SNR) — 1.0L19X068 2CXO J133650.9-295226 X065 204.212432 -29.873816 36.7 -4.652338 0.340922 0.444804 SNR — 1.0L19X069 2CXO J133651.1-295042 X067 204.213389 -29.845080 36.8 -3.305338 0.397922 1.638804 SNR — 2.0L19X070 None None 204.213872 -29.835419 35.7 -6.268338 0.037922 0.346804 HMXB — 2.0L19X072 2CXO J133651.4-295043 X071 204.214451 -29.845417 36.0 -3.104338 2.576922 2.071804 IMXB — 2.0L19X073 2CXO J133651.5-295143 X072 204.214759 -29.861982 37.1 -6.096338 -0.035078 0.405804 HMXB — 3.0L19X075 2CXO J133651.6-295025 X074 204.215290 -29.840218 36.6 -3.162338 0.319922 0.799804
SNR — 2.0L19X076 2CXO J133651.6-295335 X073 204.215325 -29.893018 37.7 -7.280838 0.126422 0.901304 HMXB — 1.0L19X077 2CXO J133651.7-295431 X076 204.215774 -29.908533 36.7 -3.217838 0.652422 1.553304 IMXB — 2.0L19X078 2CXO J133651.7-295302 X078 204.215965 -29.883780 36.3 -6.402338 0.229922 0.326804 SNR — 2.0L19X079 None X079 204.216203 -29.885984 36.2 -4.867338 0.006922 0.531804 HMXB — 2.0L19X081 None X082 204.217459 -29.827040 35.9 -4.998338 0.094922 0.338804 HMXB — 2.0L19X083 2CXO J133652.2-294920 X084 204.217900 -29.822138 36.2 -5.266338 0.346922 0.927804 HMXB — 2.0L19X084 2CXO J133652.3-295046 X085 204.218139 -29.846199 37.7 -1.705338 -0.365078 — IMXB — 1.0L19X085 None X086 204.218249 -29.883680 36.7 -4.049338 2.089922 2.414804 HMXB — 2.0L19X086 None X087 204.218388 -29.881039 36.8 -5.475338 0.266922 0.486804 HMXB — 3.0L19X087 2CXO J133652.4-295142 X088 204.218546 -29.861719 36.4 -2.238338 -0.943078 — IMXB — 3.0L19X088 CXO J133652.5-295103 None 204.219009 -29.851261 35.8 -7.638338 -0.088078 0.042804 HMXB — 2.0L19X089 2CXO J133652.5-295531 X090 204.219156 -29.925330 36.5 -4.502838 1.688422 1.740304 HMXB — 2.0L19X090 2CXO J133652.5-295147 X091 204.219227 -29.863190 36.5 -8.423338 0.054922 0.223804
HMXB
SNR — 2.0L19X098 2CXO J133652.8-295137 X098 204.220513 -29.860440 36.7 -7.602338 0.642922 0.857804
SNR — 2.0
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X099 2CXO J133652.9-295309 X101 204.220981 -29.886100 36.5 -3.602838 0.240422 0.830304
SNR — 2.0L19X100 None X100 204.220987 -29.871077 36.0 -2.139338 0.613922 1.918804 SNR — 1.0L19X101 2CXO J133653.1-295002 X102 204.221333 -29.834030 36.3 -3.302338 0.070922 1.662804 IMXB — 2.0L19X102 2CXO J133653.1-295430 X103 204.221547 -29.908382 37.1 -6.756838 1.529422 1.927304
LMXB
LMXB
SNR — 2.0L19X116 2CXO J133653.8-294848 X116 204.224490 -29.813460 36.8 -6.426338 0.072922 0.244804 SNR — 1.0L19X117 2CXO J133653.8-295101 X115 204.224492 -29.850152 36.0 -6.638338 0.260922 0.414804
SNR — 2.0L19X118 2CXO J133653.9-295114 X117 204.224743 -29.854052 37.3 -4.338338 0.765922 2.470804 HMXB — 1.0L19X119 2CXO J133654.0-294933 X118 204.225379 -29.825835 36.3 -5.633338 -0.146078 -0.081196 HMXB — 2.0L19X120 2CXO J133654.1-295308 X120 204.225678 -29.885193 36.2 -5.290338 -0.222078 0.119804
SNR — 2.0L19X121 2CXO J133654.1-295209 X119 204.225728 -29.869259 35.9 -3.361338 0.855922 1.196804 SNR — 1.0L19X122 None None 204.225818 -29.890563 36.2 -5.264838 1.679422 2.390304 HMXB — 1.0L19X123 2CXO J133654.2-295028 X121 204.226103 -29.841132 36.5 -4.692338 1.169922 2.643804 SNR — 2.0L19X124 2CXO J133654.3-295144 X122 204.226401 -29.862161 36.3 -1.749338 -1.216078 1.129804 IMXB — 1.0L19X125 2CXO J133654.4-295258 None 204.226862 -29.882823 36.5 -6.964338 0.131922 0.247804 HMXB — 1.0L19X126 2CXO J133654.4-295026 X124 204.227234 -29.840784 36.2 -6.643338 0.271922 0.383804
SNR — 2.0L19X127 None None 204.227440 -29.847208 35.5 -6.270338 0.095922 0.366804 HMXB — 2.0L19X128 None None 204.227837 -29.922301 36.3 -0.863838 — 0.719304 IMXB — 2.0L19X129 2CXO J133654.7-295300 X127 204.228412 -29.883228 36.4 -4.000338 0.410922 0.871804 SNR — 2.0L19X130 None None 204.228477 -29.885869 36.4 -5.262338 0.303922 2.087804 HMXB — 1.0L19X131 2CXO J133654.8-295018 X128 204.228694 -29.838520 36.3 -5.045338 1.340922 1.414804 SNR — 3.0L19X132 2CXO J133655.0-29523 X129 204.229362 -29.877620 36.7 -3.738338 0.767922 1.683804 SNR — 2.0L19X133 None None 204.229399 -29.880121 35.5 -3.023338 0.479922 0.775804 IMXB — 1.0L19X134 2CXO J133655.0-295304 X131 204.229527 -29.884590 37.0 -1.584838 -0.729578 1.182304 SNR — 1.0L19X135 2CXO J133655.1-295040 X134 204.229837 -29.844506 36.2 -4.468338 1.587922 2.154804 SNR — 3.0L19X137 2CXO J133655.2-295403 X135 204.230095 -29.900845 36.6 -5.172838 0.218422 0.330304 (IMXB)
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X153 None None 204.235081 -29.840754 35.9 -7.446338 1.018922 1.089804 HMXB — 2.0L19X154 None None 204.235892 -29.832542 35.8 -3.858338 1.630922 2.134804 IMXB — 2.0L19X155 2CXO J133656.6-294912 X145 204.236048 -29.820090 38.2 -3.737338 -0.030078 0.838804 IMXB — 1.0L19X157 2CXO J133656.6-294819 X146 204.236146 -29.805272 36.3 -2.436338 0.434922 1.732804 IMXB — 2.0L19X158 2CXO J133656.6-295321 X147 204.236297 -29.889203 36.4 -3.604838 1.342422 1.370304 IMXB — 3.0L19X159 2CXO J133656.7-295316 X148 204.236764 -29.887861 36.0 -3.171838 0.556422 0.631304 IMXB — 3.0L19X160 None None 204.238263 -29.884303 36.0 -2.740338 -0.687078 — IMXB — 2.0L19X161 2CXO J133657.2-295147 X150 204.238605 -29.863112 36.6 -2.057338 1.486922 2.507804 IMXB — 2.0L19X162 2CXO J133657.2-295339 X152 204.238728 -29.894263 38.2 -4.423838 1.698422 2.118304 HMXB — 1.0L19X163 2CXO J133657.2-295032 X153 204.238766 -29.842158 36.5 -2.910338 0.616922 1.998804 IMXB — 3.0L19X165 2CXO J133657.3-295035 X154 204.239106 -29.843174 36.4 -5.376338 0.104922 0.054804 HMXB — 3.0L19X167 2CXO J133657.7-295039 X157 204.240386 -29.844172 36.7 -2.950338 0.826922 0.899804 IMXB — 2.0L19X169 2CXO J133657.8-295042 X158 204.240913 -29.845146 36.8 -4.201338 1.527922 2.027804 HMXB — 1.0L19X170 2CXO J133657.8-295335 None 204.241181 -29.893010 35.7 -4.021838 2.219422 3.619304 HMXB — 2.0L19X171 2CXO J133657.8-295303 X159 204.241219 -29.884058 37.1 -5.773338 0.531922 0.729804 SNR — 1.0L19X172 2CXO J133657.9-294923 X160 204.241344 -29.823139 37.5 -3.786338 0.990922 1.869804 IMXB — 1.0L19X173 None None 204.241755 -29.860046 36.6 -4.636338 -0.178078 -0.116196 HMXB — 3.0L19X174 2CXO J133658.2-295124 X161 204.242569 -29.856742 36.9 -4.827338 -0.076078 0.397804 HMXB — 1.0L19X175 2CXO J133658.2-294833 X163 204.242946 -29.809206 37.8 -7.195338 0.181922 0.407804 HMXB — 3.0L19X176 None None 204.243125 -29.857554 35.6 -5.731338 0.151922 0.481804 HMXB — 3.0L19X177 None None 204.243225 -29.863191 35.9 -1.175338 0.244922 3.291804 LMXB — 1.0L19X178 2CXO J133658.3-295104 X165 204.243343 -29.851277 37.8 -2.779338 0.236922 1.377804 Gal — 1.0L19X179 None None 204.244080 -29.860274 35.8 -2.841338 0.830922 1.917804 IMXB — 2.0L19X180 2CXO J133658.5-294819 X166 204.244105 -29.805527 36.3 -3.364338 -0.084078 -0.167696 SNR — 2.0L19X181 None None 204.244256 -29.865764 36.3 -3.629338 -0.290078 1.166804 HMXB — 1.0L19X182 2CXO J133658.6-295237 X169 204.244372 -29.876877 36.2 -4.406338 0.586922 0.882804 SNR — 1.0L19X183 2CXO J133658.6-295246 X168 204.244377 -29.879547 38.0 -3.589338 0.095922 1.235804 IMXB — 2.0L19X184 2CXO J133658.6-295106 X170 204.244502 -29.851801 36.1 -2.780338 — 1.950804 IMXB — 1.0L19X185 2CXO J133658.7-295100 X172 204.244685 -29.850131 36.4 — — — SNR — 1.0L19X186 2CXO J133658.8-294831 X173 204.245063 -29.808781 36.2 -3.492338 0.776922 2.191804 IMXB — 1.0L19X188 2CXO J133658.9-295038 X175 204.245558 -29.844024 35.9 -3.303338 -0.074078 1.906804 IMXB — 2.0L19X189 2CXO J133658.9-295024 X177 204.245728 -29.840211 35.9 -3.787338 0.153922 0.741804
SNR — 2.0L19X190 2CXO J133658.9-295218 None 204.245753 -29.871751 35.8 -4.197338 1.094922 1.825804 HMXB — 3.0L19X191 None None 204.246295 -29.867813 36.6 -4.099338 0.028922 -0.418196 HMXB — 2.0L19X192 2CXO J133659.0-295336 X178 204.246296 -29.893351 36.6 -4.056838 0.760422 1.480304
SNR — 3.0L19X193 None None 204.246415 -29.865759 36.7 -3.993338 0.131922 -0.337196 HMXB — 1.0L19X194 None X181 204.246718 -29.863284 36.1 -4.240338 0.059922 0.529804 SNR — 1.0L19X195 2CXO J133659.3-295508 X183 204.247317 -29.919041 36.6 -2.764838 1.480422 1.405304 SNR — 1.0L19X196 2CXO J133659.3-294837 X184 204.247502 -29.810278 36.2 -4.371338 1.010922 1.317304 SNR — 2.0L19X197 2CXO J133659.4-295429 None 204.247534 -29.907418 36.0 -4.122838 0.110422 0.028304
SNR — 2.0L19X198 None None 204.247562 -29.863971 36.2 — — — LMXB — 1.0L19X199 2CXO J133659.4-294959 X185 204.247803 -29.833051 38.7 -0.674338 -1.242078 1.820304 LMXB — 3.0L19X200 None None 204.247836 -29.898144 35.8 -2.709838 -0.222578 -0.631696 HMXB — 2.0L19X201 2CXO J133659.5-295204 X186 204.247919 -29.867693 36.8 — — — SNR — 1.0L19X202 2CXO J133659.5-295414 X187 204.248356 -29.903782 37.7 -3.077838 0.075422 2.250304 IMXB — 3.0L19X203 None None 204.248655 -29.872878 36.0 -6.081338 0.158922 0.332804 HMXB — 1.0L19X204 2CXO J133659.6-295108 X190 204.248674 -29.852383 36.9 — — — LMXB — 1.0
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X205 None None 204.248817 -29.865605 36.7 -4.902338 0.451922 1.201804 HMXB — 1.0L19X206 None None 204.248945 -29.817812 34.9 -3.476338 0.277922 -0.391696 IMXB — 1.0L19X207 2CXO J133659.7-295205 X193 204.249128 -29.868135 38.2 -5.117338 0.842922 1.182804 HMXB — 2.0L19X208 2CXO J133659.8-295202 X194 204.249333 -29.867257 36.9 -5.608338 0.775922 1.978804
SNR — 2.0L19X209 2CXO J133659.8-295526 X195 204.249403 -29.923832 36.7 -5.247838 -0.044578 0.173304 SNR — 1.0L19X210 2CXO J133659.9-295150 X198 204.250025 -29.863949 38.0 -5.785338 0.085922 1.418804 HMXB — 1.0L19X211 2CXO J133659.9-295157 X197 204.250080 -29.865880 36.7 -4.781338 -0.405078 — HMXB — 3.0L19X212 2CXO J133700.0-295417 X199 204.250140 -29.904713 36.2 -2.804838 -0.377578 0.588304 SNR — 2.0L19X213 2CXO J133700.0-295219 X200 204.250210 -29.872133 36.6 -6.542338 0.378922 0.404804 HMXB — 3.0L19X214 2CXO J133700.0-295201 X202 204.250241 -29.867116 36.9 -8.779338 0.204922 0.877804 SNR — 3.0L19X215 2CXO J133700.0-295137 X201 204.250366 -29.860456 36.8 -7.133338 0.910922 1.390804 HMXB — 3.0L19X216 2CXO J133700.0-295329 X203 204.250469 -29.891541 37.4 -3.846838 0.307422 1.228304 HMXB — 1.0L19X217 2CXO J133700.1-295145 X204 204.250520 -29.862641 37.0 -5.634338 0.419922 0.913804
SNR — 3.0L19X218 2CXO J133700.2-29515 X206 204.250754 -29.864639 37.0 -6.269338 0.298922 0.797804 HMXB — 2.0L19X219 2CXO J133700.1-294810 X205 204.250844 -29.802763 36.1 -5.537338 0.412922 0.594304 SNR — 1.0L19X220 2CXO J133700.2-295206 X207 204.250918 -29.868446 37.5 -8.305338 0.126922 0.340804 SNR — 1.0L19X221 2CXO J133700.2-295150 X209 204.251179 -29.863634 37.1 -10.179338 0.872922 1.078804 HMXB — 3.0L19X222 2CXO J133700.3-295219 X211 204.251333 -29.871902 36.0 -5.131338 0.492922 1.116804
SNR — 2.0L19X223 2CXO J133700.3-295205 X212 204.251479 -29.868100 37.3 -5.870338 0.820922 1.834804 SNR — 1.0L19X224 None None 204.251619 -29.862335 36.6 -4.501338 0.912922 1.580804 HMXB — 1.0L19X225 2CXO J133700.4-295323 X215 204.251647 -29.889658 36.2 -2.194838 1.693922 -0.694696 SNR — 1.0L19X226 None None 204.251822 -29.869574 37.5 -4.694338 0.251922 1.222804 HMXB — 3.0L19X227 2CXO J133700.4-295054 X217 204.251923 -29.848393 36.2 -3.604338 2.017922 2.055804
SNR — 2.0L19X229 2CXO J133700.4-295155 X220 204.252082 -29.865412 37.5 -11.123338 0.168922 0.174804
HMXB
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X253 2CXO J133701.3-295136 X244 204.255515 -29.860115 37.9 — — — LMXB — 1.0L19X254 None None 204.256208 -29.864946 36.3 -6.528338 0.449922 1.281804 HMXB — 2.0L19X255 2CXO J133701.4-295326 X248 204.256238 -29.890672 38.4 — — — LMXB — 1.0L19X256 None X249 204.256624 -29.833032 35.8 -8.248338 0.349922 0.358304 SNR — 1.0L19X257 2CXO J133701.6-295202 X250 204.256804 -29.867168 36.5 -4.841338 0.577922 -0.047196 SNR — 1.0L19X259 2CXO J133701.6-295410 X253 204.256868 -29.902567 35.9 -5.594838 -0.081078 0.160304 SNR — 3.0L19X260 2CXO J133701.6-295128 X251 204.256872 -29.857812 38.3 -6.473338 -0.016078 -0.018196 HMXB — 1.0L19X261 None None 204.257125 -29.869639 35.1 -5.152338 -0.027078 0.235804 HMXB — 2.0L19X262 2CXO J133701.7-295113 X256 204.257301 -29.853711 36.6 -4.119338 1.025922 1.250804 SNR — 1.0L19X263 None None 204.257446 -29.865556 35.6 -4.272338 0.496922 1.614804 HMXB — 2.0L19X264 None None 204.257674 -29.855507 35.8 -4.349338 -0.191078 -0.482196 HMXB — 3.0L19X265 2CXO J133702.0-295518 X258 204.258475 -29.921617 38.2 -5.426838 0.321922 0.579304 HMXB — 2.0L19X266 None None 204.258920 -29.858617 34.8 -6.560338 0.403922 0.480804 HMXB — 2.0L19X267 2CXO J133702.1-295506 X259 204.259051 -29.918316 37.1 — — — LMXB — 1.0L19X268 2CXO J133702.1-295144 X260 204.259234 -29.862250 36.5 — — — LMXB — 1.0L19X269 2CXO J133702.2-294952 X261 204.259332 -29.831208 36.7 -3.507338 0.445922 1.837304 SNR — 2.0L19X270 None None 204.259442 -29.808982 35.9 — — — LMXB — 2.0L19X271 None X262 204.259722 -29.835170 35.9 -4.053338 0.164922 0.289304 SNR — 2.0L19X272 None None 204.259797 -29.865056 35.2 -4.395338 0.827922 1.285804 HMXB — 1.0L19X274 2CXO J133702.3-295206 X264 204.259986 -29.868488 35.6 -3.987338 1.560922 1.634804 HMXB — 2.0L19X275 2CXO J133702.4-295126 X265 204.260161 -29.857241 37.1 -7.133338 1.073922 1.036804 SNR — 2.0L19X276 None None 204.260180 -29.855700 35.5 -5.217338 0.495922 0.652804 HMXB — 3.0L19X277 None None 204.260267 -29.849892 35.9 -4.909338 0.042922 0.584804 HMXB — 2.0L19X278 2CXO J133702.4-295319 X267 204.260317 -29.888617 37.6 -4.087838 1.191922 2.258304 IMXB — 2.0L19X279 2CXO J133702.5-295345 X268 204.260561 -29.895838 36.6 -6.380838 1.872922 2.115304 AGN — 1.0L19X280 None None 204.261100 -29.860463 35.8 -5.504338 0.167922 0.618804 HMXB — 1.0L19X281 2CXO J133702.6-294824 X269 204.261125 -29.806707 36.3 — — — LMXB — 2.0L19X282 None None 204.261759 -29.861769 36.1 -7.305338 0.479922 0.784804 HMXB — 1.0L19X284 None None 204.262218 -29.850328 35.8 — — — LMXB — 1.0L19X285 2CXO J133703.0-294945 X272 204.262630 -29.829247 36.7 -3.730338 1.515922 2.217304 SNR — 1.0L19X286 None None 204.262666 -29.863842 35.6 -5.064338 0.292922 0.539804 HMXB — 2.0L19X287 2CXO J133703.1-295531 X273 204.263289 -29.925465 36.1 -2.863838 -0.267078 -0.392696 HMXB — 2.0L19X288 2CXO J133703.2-295226 X274 204.263767 -29.874059 37.3 -5.749338 1.385922 1.443804 HMXB — 1.0L19X289 2CXO J133703.4-295401 X275 204.264438 -29.900583 36.0 -6.417838 0.455922 1.831304 SNR — 1.0L19X290 2CXO J133703.5-295331 X277 204.264701 -29.891999 36.3 -2.941838 2.524922 2.256304 IMXB — 1.0L19X291 2CXO J133703.5-295320 X278 204.264887 -29.888801 36.1 -4.892838 0.167922 0.493304 HMXB — 3.0L19X292 2CXO J133703.5-294940 X279 204.265002 -29.828012 37.1 -4.642338 0.143922 0.878304 SNR — 1.0L19X293 2CXO J133703.8-294930 X281 204.266225 -29.825069 38.1 -4.393338 0.073922 -0.259696 HMXB — 3.0L19X294 2CXO J133703.9-295322 X282 204.266411 -29.889431 35.6 -2.986838 5.050922 2.352304 IMXB — 2.0L19X295 2CXO J133704.0-294915 None 204.266859 -29.820918 35.7 -5.454338 0.385922 0.449304
SNR — 2.0L19X296 2CXO J133704.1-295312 X283 204.267497 -29.886715 36.1 -3.995838 0.229922 0.186304 IMXB — 1.0L19X297 None None 204.267895 -29.849492 35.9 -3.382338 -0.039078 0.439804 IMXB — 2.0L19X298 2CXO J133704.2-295403 X284 204.267930 -29.900963 38.4 -5.524838 1.744922 1.866304 HMXB — 1.0L19X299 2CXO J133704.3-295138 None 204.268024 -29.860835 35.8 -3.838338 -0.067078 -1.044196 HMXB — 2.0L19X300 2CXO J133704.3-295130 X285 204.268298 -29.858503 37.4 — — — LMXB — 1.0L19X301 2CXO J133704.3-295121 X286 204.268307 -29.855947 38.7 -4.448338 0.076922 0.438804 IMXB — 2.0L19X302 2CXO J133704.4-294938 X287 204.268437 -29.827424 36.5 -6.074338 0.076922 0.125304 SNR — 1.0
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X303 2CXO J133704.5-294935 X288 204.268922 -29.826457 36.1 -5.335338 0.085922 0.257304 SNR — 1.0L19X304 2CXO J133704.6-295120 X290 204.269450 -29.855636 36.7 -7.837338 0.770922 1.168804
LMXB
SNR — 2.0L19X310 None None 204.270196 -29.849732 36.0 -6.190338 0.180922 0.353804 HMXB — 2.0L19X311 2CXO J133704.9-295339 X298 204.270514 -29.894318 36.0 -6.109838 0.161922 0.516304 HMXB — 1.0L19X313 None None 204.271023 -29.845851 35.9 -3.813338 1.045922 1.033804 IMXB — 1.0L19X314 2CXO J133705.1-295207 X299 204.271460 -29.868606 39.5 — — — LMXB — 1.0L19X315 2CXO J133705.2-295122 X301 204.272008 -29.856042 36.3 -3.817338 1.095922 1.278804 HMXB — 1.0L19X316 2CXO J133705.4-295234 X303 204.272890 -29.876093 37.7 -6.156338 0.094922 0.165804 HMXB — 1.0L19X317 2CXO J133705.5-295032 X304 204.273174 -29.842251 35.7 — — —
SNR — 2.0L19X318 None None 204.273282 -29.896005 36.1 -3.878838 0.829922 1.342304 HMXB — 3.0L19X321 2CXO J133705.7-294923 X307 204.274019 -29.823049 35.8 — — — LMXB — 1.0L19X322 None None 204.274234 -29.884151 35.4 -4.892838 -0.069078 0.138304 HMXB — 3.0L19X323 2CXO J133705.8-294822 X308 204.274425 -29.806105 36.1 -4.672338 1.986922 2.654304 HMXB — 3.0L19X324 None None 204.274528 -29.845933 35.7 -5.789338 0.932922 1.156804 HMXB — 1.0L19X325 2CXO J133705.9-295159 X309 204.275044 -29.866367 36.8 — — — LMXB — 1.0L19X326 2CXO J133706.0-295514 X310 204.275163 -29.920637 37.0 -3.151838 0.218922 1.568304 SNR — 2.0L19X327 2CXO J133706.1-295444 X311 204.275854 -29.912251 36.6 -3.682838 0.135922 1.016304 SNR — 1.0L19X328 2CXO J133706.4-295025 X313 204.277094 -29.840466 36.2 — — — SNR — 1.0L19X329 2CXO J133706.6-294944 X314 204.277612 -29.828967 36.0 -6.992338 0.060922 0.016304 HMXB — 1.0L19X330 2CXO J133706.6-295332 X316 204.277780 -29.892397 36.8 -3.981838 -0.032078 1.293304 SNR — 1.0L19X331 2CXO J133706.7-294947 None 204.278150 -29.829896 35.8 -3.883338 1.332922 1.949304 IMXB — 2.0L19X332 2CXO J133706.7-295057 X317 204.278281 -29.849385 36.4 — — —
SNR — 2.0L19X333 2CXO J133706.9-294934 X318 204.278904 -29.826148 36.1 -6.293338 0.486922 0.321304 HMXB — 3.0L19X334 None X319 204.279230 -29.818859 36.1 -7.146338 0.138922 0.298304 SNR — 1.0L19X335 2CXO J133707.0-295321 X320 204.279592 -29.889145 35.9 -3.765838 -0.006078 -0.262696 SNR — 3.0L19X336 None None 204.279624 -29.824184 35.4 -5.561338 0.430922 0.531304
IMXB
SNR — 2.0L19X339 None None 204.280029 -29.852327 36.1 -6.039338 1.520922 2.959804 HMXB — 2.0L19X341 2CXO J133707.4-295133 X326 204.281242 -29.859223 36.4 — — — LMXB — 1.0L19X342 2CXO J133707.5-294859 X327 204.281403 -29.816437 36.7 -5.663338 0.082922 0.001304
SNR — 2.0L19X343 2CXO J133707.5-294918 X328 204.281566 -29.821869 36.4 — — —
SNR — 2.0L19X344 None None 204.282128 -29.854122 35.9 -6.035338 0.114922 0.122804 HMXB — 3.0L19X345 2CXO J133707.6-295056 X329 204.282180 -29.849199 35.9 -6.819338 -0.038078 0.074804 HMXB — 2.0L19X346 None None 204.282844 -29.852630 36.1 -6.253338 -0.009078 -0.186196 HMXB — 1.0L19X347 None None 204.283025 -29.886275 35.9 -6.547838 0.301922 0.488304 HMXB — 2.0L19X348 2CXO J133708.1-294916 X332 204.283111 -29.822176 36.1 -3.524338 0.929922 1.332304 IMXB — 2.0L19X349 None None 204.283186 -29.870819 35.7 -5.493338 0.251922 0.699804 HMXB — 2.0L19X350 None None 204.283594 -29.893338 36.0 -3.222838 -0.159078 1.279304 Gal — 2.0L19X351 2CXO J133708.1-294916 X332 204.284202 -29.821319 36.5 -5.672338 0.279922 0.453304
IMXB
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFL19X355 None None 204.285014 -29.882153 35.9 -7.009838 -0.022078 0.639304
HMXB
HMXB
SNR — 2.0L19X368 None None 204.288484 -29.872424 35.1 -7.039338 0.278922 0.641804
IMXB
SNR — 2.0L19X393 2CXO J133712.5-295154 X366 204.302268 -29.865210 37.9 -2.360838 2.099422 1.479304 IMXB — 1.0L19X397 None None 204.304532 -29.860677 35.8 -9.145838 0.669422 0.804304 HMXB — 1.0L19X398 2CXO J133713.1-295238 X370 204.304836 -29.877253 37.1 -3.087838 0.129422 0.490304 IMXB — 2.0L19X399 2CXO J133713.6-295200 X371 204.306826 -29.866604 35.8 -3.141838 1.398422 0.885304 IMXB — 1.0L19X404 2CXO J133714.4-295130 X377 204.310070 -29.858389 36.3 -3.367838 0.140422 1.454304 IMXB — 1.0L19X405 2CXO J133714.4-295148 X378 204.310268 -29.863543 37.5 -6.928838 0.839422 1.533304 HMXB — 1.0L19X408 2CXO J133715.0-295138 X381 204.312594 -29.860764 36.4 -3.456838 0.010422 1.479304 IMXB — 1.0L19X411 2CXO J133716.2-295202 X384 204.317597 -29.867252 37.1 -2.235838 0.768422 1.841304 IMXB — 1.0L19X416 2CXO J133717.2-295153 X389 204.321772 -29.864823 37.2 -4.704838 -0.053578 0.792304 SNR — 1.0L19X418 2CXO J133717.2-295153 X389 204.322682 -29.864955 36.7 -4.454838 0.705422 1.395304
SNR — 3.0L19X421 2CXO J133718.3-295118 X395 204.326666 -29.855128 36.2 -2.503838 1.075422 1.874304 LMXB — 2.0L19X422 2CXO J133718.8-295013 X397 204.328798 -29.837096 36.6 -4.332838 0.759422 1.233304 HMXB — 1.0L19X426 2CXO J133719.6-295131 X402 204.331892 -29.858775 37.2 -6.515838 1.526422 1.710304 AGN — 1.0L19X430 2CXO J133720.8-295035 None 204.336415 -29.842960 36.3 -2.718838 0.832422 1.422304 IMXB — 3.0L19X432 2CXO J133721.1-295242 X408 204.338018 -29.878454 36.1 -2.010838 1.559422 1.729304 LMXB — 3.0L19X433 2CXO J133721.4-295121 X409 204.339367 -29.856001 36.4 — — — LMXB — 1.0L19X434 2CXO J133722.1-295208 X412 204.342371 -29.868862 37.0 -5.258838 — 3.021304 AGN — 2.0
Table A.2 continued Table A.2 (continued)
ID CSC ID Long ID R.A. Dec L X V B-V V-I Class Cluster Age CFN
OTE —Properties and classifications of all M83 X-ray sources identified in Lehmer et al. (2019) that fall within the footprint of the HST image. For each source,the ID indicates the ID number assigned in Lehmer et al. (2019), while CSC ID is the full ID from the
Chandra
Source Catalog Release 2, and Long ID isthe ID from Long et al. (2014), where applicable. X-ray Luminosities are in units log erg s − , and magnitudes are absolute mags estimated at a distance of4.61 Mpc. The classification for each source is given, with italics representing SNRs identified using our HR-L X criterion or XRBs associated with clusters.Classifications in parentheses are objects with uncertain “candidate” classifications, as reported in Long et al. (2014) or as found by our methods. Sources thatwere identified as candidate quasars are labeled ‘Gal.’ For XRBs in clusters, the cluster ages are given in units log years. A confidence flag (CF) is assigned toeach source based on the “strength” of the identification of the X-ray emitter: a CF of 1 represents the most certain classifications (those determined in otherstudies, or XRBs with a clear donor, with multiple candidates of similar mass, or a clear absence of a donor); CF ratings of 2 or 3 may indicate that a source isin a dust-obscured region, such as near the nucleus or along a dust lane (since the presence of heavy dust could potentially mask high-mass stars, backgroundgalaxies, and clusters, leading to possible mis-identifications), or that there are multiple sources of different masses within the 2- σ radius. Figure A.2.