Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. I. The nature of the companion star
Sylvain Chaty, Farid Rahoui, Cédric Foellmi, John A. Tomsick, Jérôme Rodriguez, Roland Walter
aa r X i v : . [ a s t r o - ph ] A p r Astronomy&Astrophysicsmanuscript no. integral c (cid:13)
ESO 2018November 2, 2018
Multi-wavelength observations of Galactic hard X-ray sourcesdiscovered by INTEGRAL. ⋆ I. The nature of the companion star
S. Chaty , F. Rahoui , , C. Foellmi , J. A. Tomsick , J. Rodriguez , and R. Walter Laboratoire AIM, CEA / DSM - CNRS - Universit´e Paris Diderot, Irfu / Service d’Astrophysique, Bˆat. 709, CEA-Saclay, FR-91191 Gif-sur-Yvette Cedex, France, e-mail: [email protected] ESO, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile Laboratoire d’Astrophysique, Observatoire de Grenoble, BP 53, F-38041 Grenoble Cedex 9, France Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA INTEGRAL Science Data Centre, Chemin d’ ´Ecogia 16, CH-1290 Versoix, SwitzerlandReceived November 2, 2018; accepted November 2, 2018
ABSTRACT
Context. (abridged) The
INTEGRAL hard X-ray observatory has revealed an emerging population of highly obscured X-ray binary systemsthrough multi-wavelength observations. Previous studies have shown that many of these sources are high-mass X-ray binaries hosting neutronstars orbiting around luminous and evolved companion stars.
Aims.
To better understand this newly-discovered population, we have selected a sample of sources for which an accurate localisation isavailable to identify the stellar counterpart and reveal the nature of the companion star and of the binary system.
Methods.
We performed an intensive study of a sample of thirteen
INTEGRAL sources, through multi-wavelength optical to NIR photometricand spectroscopic observations, using EMMI and SofI instruments at the ESO NTT telescope. We performed accurate astrometry and identifiedcandidate counterparts for which we give the optical and NIR magnitudes. We detected many spectral lines allowing us to determine the spectraltype of the companion star. We fitted with stellar black bodies the mid-infrared to optical spectral energy distributions of these sources. Fromthe spectral analysis and SED fitting we identified the nature of the companion stars and of the binary systems.
Results.
Through spectroscopic analysis of the most likely candidates we found the spectral types of IGR J16320-4751, IGR J16358-4726,IGR J16479-4514, IGR J17252-3616, IGR J18027-2016: They all host OB type supergiant companion stars, with IGR J16358-4726 likelyhosting an sgB[e]. Our spectra also confirm the supergiant O and B nature of IGR J17391-3021 and IGR J19140 + Conclusions.
Key words.
Infrared: stars – X-rays: binaries, individuals: IGR J16320-4751, IGR J16358-4726, IGR J16393-4643, IGR J16418-4532, IGR J16479-4514, IGR J16558-5203, IGR J17091-3624, IGR J17252-3616, IGR J17391-3021, IGR J17597-2201, IGR J18027-2016,IGR J18483-0311, IGR J19140 +
1. Introduction
The hard X-ray
INTEGRAL observatory was launched on the17th of October 2002, and since then, it has performed a de-tailed survey of the Galactic plane. The ISGRI detector onthe IBIS imager (Lebrun et al. 2003) has discovered many
Send o ff print requests to : S. Chaty ⋆ Based on observations collected at the European Organisationfor Astronomical Research in the Southern Hemisphere, Chile (ESOProgramme 073.D-0339) (PI S. Chaty). new hard X-ray sources , including binary systems, pulsarsand AGNs, all these so-called IGR sources being reportedin Bird et al. (2007) and Bodaghee et al. (2007). One of themost important achievements of the INTEGRAL observatoryto date is that it is revealing hard X-ray sources which werenot easily detected in earlier soft X-ray (typically ≤
10 keV)observations, bringing to light a previously hidden part of An updated list of these sources is maintained athttp: // isdc.unige.ch / ∼ rodrigue / html / igrsources.html. S. Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems a population of highly obscured high-energy binary systemsin our Galaxy. These objects share characteristics that haverarely been seen (see Dean et al. 2005). They are high-massX-ray binaries (HMXBs) hosting a neutron star orbiting anOB companion star, in some cases a supergiant star (seee.g. Filliatre & Chaty 2004 and Pellizza et al. 2006), some ofthem possibly being long-period X-ray pulsars. Many of thesenew sources are highly absorbed, exhibiting column densitieshigher than about 10 cm − , and are concentrated in directionstangential to Galactic arms, for instance the Norma arm (seeChaty & Filliatre 2005, Tomsick et al. 2004a and Walter et al.2004b), the richest arm of our Galaxy in high-mass star form-ing regions. This short-lived population hosts the likely pro-genitors of extremely compact binary objects, which are goodcandidates of gravitational wave emitters, and might constitutea key sample in the understanding of the evolution of high-energy binary systems.Among these HMXBs hosting an OB supergiant com-panion star, two classes, which might overlap, appear(Chaty & Rahoui 2006). The first class is constituted ofintrinsically highly obscured hard X-ray sources, exhibit-ing a huge local extinction. The most extreme example ofthese sources is the highly absorbed source IGR J16318-4848 (Filliatre & Chaty 2004). The second class exhibits fastand transient outbursts, with peak fluxes of the order of10 − erg s − cm − in the 20 −
40 keV band, and lasting onlya few hours. This last characteristic is very unusual amongHMXBs. For this reason they are called Supergiant Fast X-rayTransients (SFXTs, Negueruela et al., 2006b). These SFXTshave faint quiescent emission, and their hard X-ray spectrarequire a black hole or neutron star accretor. Among thesesources, IGR J17544-2619 (Pellizza et al. 2006) seems to bethe archetype of this new class of HMXBs, with long quies-cent periods (Zurita Heras & Chaty in prep.).Even if the
INTEGRAL observatory can provide a locali-sation that is accurate above 10 keV ( ∼ ′ ), it is not accurateenough to pinpoint the source at other wavelengths, which isnecessary to reveal the nature of these sources. So the first stepin the study of these sources is to look for an accurate localisa-tion of the hard X-ray sources by X-ray satellites such as XMM-Newton , Swift or Chandra . While
XMM-Newton and
Swift pro-vide positions good enough to restrict the list of possible coun-terparts to a small number, only
Chandra gives unique identi-fications in most cases (see for instance the multi-wavelengthstudy of four
INTEGRAL sources in the direction of the Normaarm by Tomsick et al. 2006, via
Chandra localisation). Oncethe source position is known to better than several arcseconds,the hunt for the optical counterpart of the source can begin.However, a di ffi culty persists, due to the high level of interstel-lar absorption in this region of the Galaxy, close to the Galacticplane. Near-infrared (NIR) observations, thanks to accurate as-trometry, and photometric and spectroscopic analysis, allowfor the nature of these sources to be revealed, constraining thespectral type of the companion star and the type of the binarysystem.Finally, mid-infrared (MIR) observations are required tounderstand why these sources exhibit a strong local absorption,by characterizing the nature of the absorbing matter, and de- termining whether it is made of cold gas or dust, or anythingelse. Based on the optical / NIR observations we report here, wehave performed MIR observations with the VISIR instrumenton ESO VLT / UT3. These observations, focusing on the charac-terization of the presence, temperature, extension and compo-sition of the absorbing material constituting the circumstellarmedium enshrouding the obscured sources, are described in acompanion paper by Rahoui et al. (2008).Here we report on an intensive multi-wavelength study ofa sample of 13
INTEGRAL sources belonging to both obscuredand SFXT classes, for which accurate X-ray localisations areavailable, aimed at identifying their counterparts and constrain-ing the nature of the companion star and of the binary system.We first describe the ESO optical / NIR photometric and spec-troscopic observations, and build the spectral energy distribu-tions (SEDs) in Section 2. We then review hard X-ray proper-ties of each source, and report the results of our optical / NIRobservations in Section 3. We give general results and discussthem in Section 4, and provide our conclusions in Section 5.
2. Observations
The multi-wavelength observations that we describe here arebased on astrometry, photometry and spectroscopy on 13
INTEGRAL sources indicated in Table 1. They were performedat the European Southern Observatory (ESO, Chile), in 2domains: in optical (0 . − . µ m) with the EMMI instru-ment and in NIR (1 − . µ m) with the SofI instrument, bothwith the 3.5m New Technology Telescope (NTT) at La SillaObservatory. Our optical and NIR observations were carriedout as part of the programme ESO . On 2004 July 10 between UT 0.0 and 11.0 we obtained opticalphotometry in B , V R , I and Z bands of the sources given inTable 2 with the spectro-imager EMMI, installed on the NTT.We used the large field of EMMI’s detector, with the imagesbinned by a factor of 2, giving an image scale of 0. ′′ / pixeland a field of view of 9. ′ × ′
0. The photometric observa-tions were performed with an integration time between 1 and30 s for each exposure, as reported in Table 2. We observedfive photometric standard stars of the optical standard star cat-alogue of Landolt (1992): PG 1633 + + + + + ′′ . The reduced data are available for retrieval at http: // wikimbad.org.. Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 3
Finally, through internal Director’s Discretionary Time(DDT) we obtained long-slit low-resolution spectra of 2sources –IGR J17252-3616 and IGR J18027-2016– with thespectro-imager EFOSC2 installed on the 3.6 m telescope of LaSilla Observatory.
We performed NIR photometry in J , H and K s bands of thesources given in Table 1 on 2004 July 08-11 with the spectro-imager SofI, installed on the NTT. We used the large field ofSofI’s detector, giving an image scale of 0. ′′ / pixel and afield of view of 4. ′ × ′
92. The photometric observations wereobtained by repeating a set of images for each filter with 9 dif-ferent 30 ′′ o ff set positions including the targets, following thestandard jitter procedure allowing us to cleanly subtract the skyemission in NIR. The integration time varied between 10 and50 s for each individual exposure, giving a total exposure timebetween 108 and 450 s. The NIR photometry results are givenin Table 4. We observed three photometric standard stars ofthe faint NIR standard star catalogue of Persson et al. (1998):sj9157, sj9172 and sj9181.We also carried out NIR spectroscopy with SofI between0.9 and 2 . µ m, taking 12 spectra using alternatively the low-resolution Blue and Red grisms respectively, half of them withthe 1. ′′ ff set of30 ′′ , in order to subtract the NIR sky emission. Each individ-ual spectrum has an exposure time from 60 to 180 s, giving atotal integration time between 720 and 2160 s in each grism, asreported in Table 3. We used the IRAF (Image Reduction and Analysis Facility)suite to perform data reduction, carrying out standard pro-cedures of optical and NIR image reduction, including flat-fielding and NIR sky subtraction.We performed accurate astrometry on each entire SofI4. ′ × ′
92 field, using all stars from the 2MASS cataloguepresent in this field (amounting to ∼ ′′
5, and we ob-tained a pixel scale in x,y axis of − ′′ ′′ / pixelrespectively. The finding charts including the results of our as-trometry are shown in Figures 2 and 3 for all sources of oursample.We carried out aperture photometry, and we then trans-formed instrumental magnitudes into apparent magnitudes us-ing the standard relation: mag app = mag inst − Z p − ext × AM where mag app and mag inst are the apparent and instrumentalmagnitudes, Zp is the zero-point, ext the extinction and AM theairmass. We used for the extinction ext J = . ext H = . ext Ks = .
10 typical of the La Silla observatory. The logof the observations and the results of photometry are given inTables 2 and 4 for the optical and NIR respectively. The pixel size of 2MASS is 2. ′′ ∼ ′′ We analyzed the optical spectra using standard IRAF tasks,subtracting bias and correcting for flat field, and we used the
IRAF noao.twodspec package in order to extract spectra andperform wavelength and flux calibrations. The optical spec-tra were reduced and flux-calibrated in “F-lambda” units -erg cm − s − Å.NIR spectra were reduced using IRAF by flat-fielding, cor-recting the geometrical distortion using the arc frame, shiftingthe individual images using the jitter o ff sets, combining theseimages and finally extracting the spectra. The analysis of SofIspectroscopic data, and more precisely the sky subtraction, wasdi ffi cult due to a variable sky, mainly in the red part of the bluegrism, causing some wave patterns. The target spectra werethen corrected for the telluric lines using a median of variousstandard stars observed with the same configuration during thecorresponding nights. All spectra, optical and NIR, are finallyshifted to the heliocentric rest frame. Once the most likely counterpart was identified through as-trometry, photometry and spectroscopy when available, wewere able to build the optical / NIR SEDs of all sources ofour sample, shown in Figure 1. While these SEDs are mainlybased on optical and NIR photometry from this paper, wealso add MIR observations (5 − µ m) obtained with theVISIR instrument on Melipal, the 8 m third Unit Telescope(UT3) of the ESO Very Large Telescope (VLT) at ParanalObservatory, reported in the companion paper by Rahoui et al.(2008). We also put MIR data taken from the Spitzer
GLIMPSEsurvey, reported in Rahoui et al. (2008), and in Table 5 forthe sources not included in this companion paper. We in-clude in these SEDs data from X-ray observations taken with
INTEGRAL / IBIS for all the sources,
XMM for IGR J16418-4532, IGR J17252-3616 and IGR J19140 + RXTE forIGR J16358-4726, IGR J17091-3624, IGR J17597-2201 andIGR J17391-3021,
ASCA for IGR J16320-4751, IGR J16393-4643 and IGR J16479-4514,
BeppoSAX for IGR J18027-2016,and finally
INTEGRAL / JEM-X for IGR J18483-0311.We fitted the optical to MIR observing data with a blackbody emission reproducing the stellar emission. The broadband SEDs of these sources were modelled using an absorbedblack body emission component, representing the companionstar emission ( D ∗ and R ∗ are respectively the distance and ra-dius of the star): λ F ( λ ) = π hc D ∗ λ − . A λ " R ∗ e hc λ kT ∗ − in W.m − (1)The free parameters of the fits were the absorption in theV band Av, the companion star black body temperature T ∗ andits R ∗ D ∗ ratio. The fits were performed using a χ minimization.Best-fitting parameters for individual sources, as well ascorresponding χ and 90%–confidence ranges of parame-ters, are reported in Table 6 for the sources IGR J16393-4643, IGR J16418-4532, IGR J17091-3624, IGR J17597-2201,IGR J18027-2016 and IGR J18483-0311, and in Rahoui et al.(2008) for the remaining sources. The IGR J16558-5203 SED S. Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems has not been fitted, because of its AGN nature. In this Table wealso give the interstellar extinction in magnitude, A i , obtainedfrom the neutral hydrogen column density N HI , and the X-rayextinction in magnitude, A X , obtained from X-ray observations.Both extinctions were converted to magnitudes using the con-version between N H and A v given by Predehl & Schmitt (1995). N HI has been computed using the N H tool from HEASARC (Dickey & Lockman 1990). Since N HI is the total galactic col-umn density along the line of sight, it is likely overestimatedcompared to the real value at the distance of the sources.We overplot on the SEDs of Figure 1 the best-fitted modelto our observations. The dip seen at ∼ × Hz is due to sil-icate absorption present in our extinction model (more detailson this model are given in Rahoui et al. 2008).
3. Results on individual sources
All the sources studied in this paper were discovered with theIBIS / ISGRI detector onboard the
INTEGRAL observatory. Thesample of 13 sources, along with their position, uncertainty,and references about their discovery and position are given inTable 1. We present in the following our results on each source,for which we followed the same strategy. We first observed thefield in optical and NIR, we performed accurate astrometry, andwe derived the photometry of the candidates inside the X-raysatellite error circle. We then analyzed the optical / NIR spec-trum of the most likely candidate, when available. We give theresults of the optical-MIR SED fitting.
IGR J16320-4751 was discovered on 2003 February byTomsick et al. (2003) at the position RA = h m = − ◦ ′ (equinox J2000.0; uncertainty 2 ′ ). Follow-up XMM-Newton observations localized the source at16 h m s − ◦ ′ ′′ with 3 ′′ accuracy (Rodriguez et al.2003; Rodriguez et al. 2006). It is a heavily absorbed vari-able source with N H ∼ . × cm − , and a hard X-ray spectrum fitted by an absorbed power-law, with Γ ∼ . ∼ ±
40 s with
XMM-Newton and P ∼ ±
50 s with
ASCA observations, these pul-sations being the signature of an X-ray pulsar (Lutovinov et al.2005b). An orbital period of 8 . ± .
01 days was found froma
Swift / BAT lightcurve extending from 2004 December 21 to2005 September 17 (Corbet et al. 2005), and of 8 . ± .
05 dayswith
INTEGRAL (Walter et al. 2006). Putting the spin and or-bital periods of this source on a Corbet diagram (Corbet 1986)suggests a supergiant HMXB nature. IGR J16320-4751 mighthave been persistent for at least 8 years, since this source is therediscovery of a previously known
ASCA source AX J1631.9-4752.We performed accurate astrometry of the field (rms offit = ′′ ′′ XMM-Newton error circle in thefinding chart of Figure 2. We give the infrared magnitudes ofall the candidate counterparts in Table 4. Two candidate coun- http: // heasarc.gsfc.nasa.gov / cgi-bin / Tools / w3nh / w3nh.pl terparts had been proposed for this source (Rodriguez et al.2003), however the XMM-Newton ′′ error circle made theambiguity disappear, accurately localizing the candidate la-beled 1 in Figure 2, and making it the most likely counterpart(2MASS J16320215-4752289; Rodriguez et al. 2006). This re-sult is in agreement with Negueruela & Schurch (2007) reject-ing candidate 2 on the basis of 2MASS photometry. In addition,Candidate 1 is much more absorbed than Candidate 2, as canbe seen from the optical and NIR magnitudes given for bothcandidate counterparts in Tables 2 and 4, since Candidate 1 isinvisible in the optical, but becomes as bright as Candidate 2in the K S band. There are at least two faint candidate coun-terparts (labeled 3 and 4) inside the error circle, therefore itwould be useful to obtain a more accurate position to unam-biguously pinpoint the correct counterpart. However, the faint-ness of Candidates 3 and 4 tends to rule them out as counter-parts, and in the following we will consider Candidate 1 as themost likely counterpart of this source.NIR spectra of candidate 1 of IGR J16320-4751 are shownin Figure 4. We report the detected lines in Table 8. There areonly a few lines visible in the blue NIR spectrum, probablybecause it is very faint and absorbed. The red NIR spectrumexhibits a very red continuum, and the presence of absorp-tion and emission lines: the Pa(7-3) emission line, the Brackettseries with P-Cygni profiles between 1.5 and 2 . µ m, andHe i at 2 . µ m (perhaps with P-Cygni profile). The presenceof these narrow and deep Paschen and He i lines, associatedwith P-Cygni profiles, are typical of early-type stars, and moreprecisely of luminous supergiant OB stars (Caron et al. 2003,Munari & Tomasella 1999), which is therefore the likely spec-tral type of the companion star. Furthermore, the presence ofa wide Br γ emission line constrains the spectral type to a Osupergiant or even O hypergiant (Hanson et al. 2005). We alsotook optical and NIR spectra of Candidate 2: they do not ex-hibit any emission lines, and seem typical of a late-type star.Such a spectral type would therefore be hard to reconcile withthe wind accretion hard X-ray spectra and the localisation ofthis source in the Corbet diagram. Therefore both astrometryand spectroscopy allow us to exclude Candidate 2 as a candi-date counterpart. These results strengthen Candidate 1 as thereal counterpart of IGR J16320-4751. From the nature of thecompanion star and of the compact object, we derive that thissource belongs to the very obscured supergiant HMXB class,hosting a neutron star. This result is also in agreement with thefit of its SED, computed in Rahoui et al. (2008) and shown inFigure 1. IGR J16358-4726 was discovered on 2003 March 19 byRevnivtsev et al. (2003b) at the position (RA DEC J2000.0) = (16 h m − ◦ ′ , 1. ′ Chandra duringa scheduled observation of SGR 1627-41 on 2003 March 24.
Chandra localized the source at (16 h m s − ◦ ′ ′′ ′′ . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 5
Table 1.
Sample of sources. Name and coordinates of the sources: position (RA, DEC, J2000.0), galactic longitude and lat-itude (l,b), uncertainty (Unc. in arcmin) and reference (Ref1) of the discovery of the source by
INTEGRAL ; and position(RA, DEC, J2000.0), uncertainty (Unc.) and reference (Ref2) of the most accurate position by the satellite indicated in paren-thesis. References are b: Bodaghee et al. (2006), c: Chernyakova et al. (2003), h: Hannikainen et al. (2003), i: in’t Zand et al.(2006), ke: Kennea & Capitanio (2007), ko: Kouveliotou et al. (2003), ku: Kuulkers et al. (2003), l3: Lutovinov et al. (2003), ma:Malizia et al. (2004), mo: Molkov et al. (2003), re2: Revnivtsev et al. (2003b), re4: Revnivtsev et al. (2004), ro: Rodriguez et al.(2006), sg: Sguera et al. (2007), sm: Smith et al. (2006), st: Stephen et al. (2005), su: Sunyaev et al. (2003), t3: Tomsick et al.(2003), t4: Tomsick et al. (2004b), w4: Walter et al. (2004a), w6: Walter et al. (2006), z: Zurita Heras et al. (2006).
Source RA DEC l b Unc. Ref1 RA DEC Unc. Ref2IGR J16320-4751 248.006 -47.875 336.3 0.169 0.4 t3 16 h m s − ◦ ′ ′′ ′′ ( XMM ) roIGR J16358-4726 248.976 -47.425 337.01 -0.007 0.8 re2 16 h m s − ◦ ′ ′′ ′′ Chandra ) koIGR J16393-4643 249.775 -46.706 338.015 0.100 0.7 ma 16 h m s − ◦ ′ ′′ ′′ ( XMM ) bIGR J16418-4532 250.468 -45.548 339.19 0.489 1.0 t4 16 h m s − ◦ ′ ′′ ′′ ( XMM ) w6IGR J16479-4514 252.015 -45.216 340.16 0.124 1.4 mo 16 h m s − ◦ ′ ′′ ′′ ( XMM ) w6IGR J16558-5203 254.010 -52.062 335.687 -05.493 2.0 w4 16 h m s − ◦ ′ ′′
18 3. ′′
52 (
Swift ) stIGR J17091-3624 257.280 -36.407 349.5 2.2 0.5 ku 17 h m s − ◦ ′ ′′ ′′ Swift ) keIGR J17252-3616 261.299 -36.282 351.5 -0.354 0.5 w4 17 h m s − ◦ ′ ′′ ′′ ( XMM ) zIGR J17391-3021 264.800 -30.349 358.07 0.445 1.2 su 17 h m s − ◦ ′ ′′ ∼ ′′ ( Chandra ) smIGR J17597-2201 269.935 -22.026 7.581 0.775 0.6 l3 17 h m s − ◦ ′ ′′ ′′ ( XMM ) w6IGR J18027-2016 270.661 -20.304 9.418 1.044 0.7 re4 18 h m s − ◦ ′ ′′ ′′ ( XMM ) w6IGR J18483-0311 282.068 -3.171 29.760 -0.744 0.8 c 18 h m s − ◦ ′ ′′
54 3 . ′′ ( Swift ) sgIGR J19140 + h m s + ◦ ′ ′′
29 0. ′′ Chandra ) i
Table 2.
Results in Optical. We indicate the name of the source, the date and UT time of the observations, the airmass (AM), theexposure time in seconds (ET) and the B, V, R, I and Z magnitudes. Z-band magnitudes are instrumental.
Source Date AM ET B V R I ZIGR J16320-4751 C1 2004-07-10T03:04 1.1 30 > . ± . > . ± . > . ± . > . ± . > . ± . . ± .
04 16 . ± .
02 15 . ± .
01 13 . ± .
02 13 . ± . > . ± . > . ± .
33 23 . ± .
34 20 . ± .
10 18 . ± . > . ± .
80 21 . ± .
13 19 . ± .
05 17 . ± .
05 16 . ± . > . ± .
71 14 . ± .
02 12 . ± .
02 11 . ± .
02 10 . ± . Table 3.
Log of optical and NIR spectra. We indicate the name of the source, the telescope used, the date and UT time of theobservations, the airmass (AM), the exposure time in seconds in optical and NIR (blue and red grisms respectively). All spectrawere obtained at ESO / NTT with EMMI and SofI instruments, except the optical spectra of IGR J17252-3616 and IGR J18027-2016 obtained at ESO / Source Tel Date AM optical NIR blue grism NIR red grismIGR J16320-4751 C1 NTT 2004-07-08T23:18 1.255 - 2160 2160IGR J16320-4751 C2 NTT 2004-07-10T03:36 1.112 1440 - -” NTT 2004-07-08T23:18 1.255 - 2160 2160IGR J16358-4726 NTT 2004-07-09T02:06 1.052 - 2160 2160IGR J16479-4514 NTT 2004-07-10T23:35 1.222 - 720 720IGR J17252-3616 3.6m 2005-10-01T01:49 1.683 4800 - -” NTT 2004-07-11T01:08 1.083 - 720 720IGR J17391-3021 NTT 2004-07-10T05:36 1.177 720 - -IGR J17391-3021 NTT 2004-07-09T04:24 1.038 - 1080 1080IGR J18027-2016 3.6m 2005-09-30T02:38 2.006 1800 - -” NTT 2004-07-11T02:34 1.036 - 720 720IGR J19140 + mated since the source was 9. ′ Chandra aimpointso that the point-spread function is significantly broadened.This source is a transient source, its hard X-ray spectrum be-ing well fitted with a heavily absorbed power-law: Γ ∼ . N H ∼ . cm − , with the presence of Fe K α emission line(Patel et al. 2007). By performing detailed spectral and timing analysis of this source using multi-satellite archival observa-tions, Patel et al. (2007) have detected 5880 ±
50 s periodic vari-ations, which could be due either to the spin of a neutron star, orto an orbital period, and they identified a 94 s spin-up in 8 days,corresponding to a mean spin period derivative of 1 . × − s / s,pointing to a neutron star origin. Assuming that this spin up S. Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems
Table 4.
Results in NIR. We indicate the name of the source (C1, C2, etc. indicate the di ff erent candidates as labeled in thefinding charts of Figure 2), the date and UT time of the observations, the airmass, the exposure time (Exptime) in seconds, andthe J, H and K S magnitudes. Source Date Airmass Exptime J H K S (s) 1 . µ m 1 . µ m 2 . µ mIGR J16320-4751 C1 2004-07-08T23:05 1.3 108 17.24 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± + ± ± ± Table 5.
GLIMPSE fluxes (in mJy) for the sources IGR J16393-4643, IGR J16418-4532, IGR J18027-2016 and IGR J18483-0535. The fluxes for the other sources are given in Rahoui et al. (2008).
Sources 3 . µ m 4 . µ m 5 . µ m 8 µ mIGR J16393-4643 3 . ± .
52 2 . ± . − − IGR J16418-4532 12 . ± .
90 9 . ± .
58 5 . ± .
58 3 . ± . . ± .
28 7 . ± .
18 5 . ± .
26 2 . ± . . ± .
90 164 . ± .
20 124 . ± .
50 67 . ± . is due to accretion, they estimate the source magnetic field tobe between 10 and 10 G, suggesting that the compact ob-ject might be a magnetar. These observations suggest that thissource is an X-ray pulsar at a distance of ∼ − Chandra po-sition (2MASS J16355369-4725398, with J = = = = ′′ ′′ Chandra error circle, asshown in Figure 2. The 2MASS counterpart is at 1.2 ′′ from thecentre, therefore outside the error circle. On the other hand,this 2MASS counterpart might be a blended object, since itshows an extension towards the east, right at the position ofthe error circle. A better spatial resolution would allow usto confirm or not whether the 2MASS candidate is the real . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 7
Table 6.
Summary of parameters we used to fit the SEDs of the sources. We give their name, the interstellar extinction inmagnitudes Ai, the X-ray extinction of the source in magnitudes Ax and the parameters of the fit: the extinction in the opticalAv, the temperature T ∗ and the R ∗ D ∗ ratio of the companion (more details on these parameters are given in the text). The 90%-confidence ranges of these parameters are given in parenthesis. We also give the reduced χ . The parameters for the other sourcesare given in Rahoui et al. (2008). Sources Ai Ax Av T ∗ ( K ) R ∗ D ∗ χ / dofIGR J16393-4643 11 .
71 133 .
61 11 . . − .
8) 24400(12800 − . . − . × − . / .
05 53 .
45 14 . . − .
9) 32800(10600 − . . − . × − . / .
13 5 .
34 6 . . − .
6) 6900(3000 , . . − . × − . / .
251 24 .
05 16 . . − .
1) 31700(6500 − . . − . × − . / .
56 48 .
42 8 . − .
1) 20800(12800 − . . − . × − . / .
66 148 . . . − .
3) 22500(16400 − . . − . × − / counterpart of this source. However, its brightness favors thiscandidate, and in the following we consider it as the candidatecounterpart. Optical and NIR magnitudes of this 2MASScandidate are given in Tables 2 and 4 respectively.The NIR spectra of IGR J16358-4726 are shown in Figure4. We report the detected lines in Table 8. The NIR spectrumis very faint and extremely absorbed, however we detect somelines even in the blue part of its spectrum, mainly He ii emis-sion lines. The red part of the NIR spectrum exhibits a red con-tinuum, and the presence of absorption and emission lines, withtentative P-Cygni profiles: the H Brackett series with P-Cygniprofiles between 1.5 and 2 . µ m, and He i and He ii absorp-tion lines. The presence of these lines, associated with P-Cygniprofiles, are typical of an OB supergiant star, which is there-fore probably the spectral type of the companion star. In thiscase it would be a supergiant HMXB. In addtion, we clearlydetect the forbidden [Fe ii ] line at 2 . µ m (and tentatively theallowed Fe ii line at 1 . µ m), suggesting that the companionstar is a sgB[e] star. Furthermore, it is interesting to note thatRahoui et al. (2008) propose, using an independent method ofSED fitting, that the companion might be a sgB[e] star. Our re-sult would therefore be in agreement with the fit of its SED,shown in Figure 1. IGR J16393-4643 was discovered by Malizia et al. (2004) atthe position (RA, DEC, J2000.0) = (16 h m , − ◦ ′ ) (2 ′ un-certainty). The improved position from XMM-Newton / EPIC is(RA DEC, J2000.0) = (16 h m s , − ◦ ′ ′′ ) (4 ′′ uncer-tainty) which is compatible with that of 2MASS J16390535-4642137 (Bodaghee et al. 2006). It is a persistent, heavily-absorbed ( N H = . × cm − ), and hard ( Γ = . ± . . ± . . ± . Rossi-XTE data, im-plying a mass function of 6 . ± . M ⊙ (or up to 14 M ⊙ if the orbit is eccentric; Thompson et al. 2006), this lower limit onthe mass confirming that the system is an HMXB.We performed accurate astrometry of the field (rms offit = ′′ ′′ T ∗ = R ∗ / D ∗ ( = . × − ) minimizing χ , and assuming a radius R ∗ = R ⊙ typical of a BIV-V spectral type companion star,we derive a distance of D ∗ = . R ⊙ , we derive a distance of nearly 20 . IGR J16418-4532 was discovered on 2003 February1-5 at the position (RA DEC J2000.0) = (16 h m − ◦ ′ , 2 ′ uncertainty), towards the Norma region(Tomsick et al. 2004b). XMM-Newton localized the sourceat (16 h m s , − ◦ ′ ′′ ) with 4 ′′ accuracy (Walter et al.2006). XMM-Newton observations have shown that it is aheavily absorbed X-ray pulsar exhibiting a column density of N H ∼ . × cm − , a peak-flux of ∼
80 mCrab (20-30 keV),and a pulse period of 1246 ±
100 s (Walter et al. 2006). Thissource is an SFXT candidate, as proposed by Sguera et al.(2006) using
INTEGRAL observations. A 3 .
75 day modulationwas found in
Rossi-XTE / ASM and
Swift / BAT lightcurves, with
S. Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems ν F ν ( W / m ) ν (Hz)IGR J16320-4751 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J16358-4726 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J16393-4643 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J16418-4532 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J16479-4514 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J17091-3624 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J17252-3616 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J17391-3021 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J17597-2201 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J18027-2016 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 ν F ν ( W / m ) ν (Hz)IGR J18483-0311 1e-16 1e-15 1e-14 1e-13 1e-12 1e+13 1e+14 1e+15 1e+16 1e+17 1e+18 1e+19 1e+20 ν F ν ( W / m ) ν (Hz)IGR J19140+0951 Fig. 1.
SEDs of all these
INTEGRAL sources, showing the observations from hard X-rays to MIR wavelengths. In each case, weoverplot the black body emission representing the stellar spectral type of the companion star, which is given in Table 7 for thesources IGR J16393-4643, IGR J16418-4532, IGR J17091-3624, IGR J17597-2201, IGR J18027-2016 and IGR J18483-0535,and in Rahoui et al. (2008) for the remaining sources. See Section 2.4 for more details on the X-ray data. From top to bottom, andleft to right: IGR J16320-4751, IGR J16358-4726, IGR J16393-4643, IGR J16418-4532, IGR J16479-4514, IGR J17091-3624,IGR J17252-3616, IGR J17391-3021, IGR J17597-2201, IGR J18027-2016, IGR J18483-0311 and IGR J19140 + = ′′ XMM-Newton error circle is 2. ′′ ′′ XMM-Newton error circle, not present in the 2MASScatalogue, at 1.9, 1.3 and 2. ′′ T ∗ = . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 9(a) IGR J16320-4751 (3 ′′ XMM-Newton ) (b) IGR J16358-4726 (0.6 ′′ Chandra ) (c) IGR J16393-4643 (4 ′′ XMM-Newton )(d) IGR J16418-4532 (4 ′′ XMM-Newton ) (e) IGR J16479-4514 (4 ′′ XMM-Newton ) (f) IGR J16558-5203 (3. ′′ Swift )(g) IGR J17091-3624 (3.6 ′′ Swift ) (h) IGR J17252-3616 (4 ′′ XMM-Newton ) (i) IGR J17391-3021 (1 ′′ Chandra ) Fig. 2.
Finding charts of the studied
INTEGRAL sources, observed at ESO NTT telescope in the infrared K S band (2.2 µ m).Size: 1 ′ x1 ′ ; North is to the top and East to the left. They are all centered apart from IGR J16558-5203, because the source wascaught at the edge of the CCD. We overplot the most accurate localisation available to date.Table 6. The R ∗ / D ∗ ratio which minimizes χ ( = . × − )allows us to derive a minimal distance of 13 kpc for a super-giant, which is plausible. This source is therefore an HMXB,and could be a supergiant HMXB, consistent with its positionin the Corbet diagram. We point out however its membershipof the SFXT class is uncertain, based on its X-ray behaviour(Zurita Heras & Chaty in prep.). IGR J16479-4514 was discovered on 2003 August 8-9 at theposition (RA DEC J2000.0) = (16 h m , − ◦ ′ ), uncertainty ∼ ′ , by Molkov et al. (2003). XMM-Newton observations lo-calized the source at (16 h m s , − ◦ ′ ′′ ) with a 4 ′′ ac-curacy (Walter et al. 2006). These XMM-Newton observationshave shown a column density of N H = . − . × cm − .This source has recurrent outbursts, making it a fast transient / NIR observations revealing the obscured
INTEGRAL binary systems(a) IGR J17597-2201 (4 ′′ XMM-Newton ) (b) IGR J18027-2016 (4 ′′ XMM-Newton ) (c) IGR J18483-0311 (3.3 ′′ Swift )(d) IGR J19140 + ′′ Chandra ) Fig. 3.
Figure 2 cont’d: finding chart of the studied
INTEGRAL sources.with a peak-flux of ∼
120 mCrab (20-60 keV) (Sguera et al.2005; Sguera et al. 2006). There is an IR source IRAS 16441-4506 in the error circle.We performed accurate astrometry of the field (rms of fit = ′′ = = = ′′ XMM-Newton error circle, which isthe closest 2MASS source, suggested by Walter et al. (2006) asbeing a candidate counterpart. In addition, we find another can-didate counterpart inside the error circle, at 2. ′′ . − . µ m, and also He i , He ii andFe ii emission lines. These NIR spectra are typical of a super-giant OB star, therefore strengthening Candidate 1 as the likelycounterpart of this source, the companion star of IGR J16479-4514 having an OB spectral type. Furthermore, the presenceof a Br γ emission line and He i at 2 . µ m absorption lineconstrains the spectral type to a late O or peculiar early B su-pergiant (Hanson et al. 2005). This source would therefore be a supergiant HMXB system, probably belonging to the SFXTclass. Its SED, consistent with the HMXB nature of the system,is shown in Figure 1. IGR J16558-5203 was discovered at the position (RADEC J2000.0) = (16 h m , − ◦
03) with a 2 ′ uncer-tainty (Walter et al. 2004a). This source has a ROSAT counterpart (1RXS J165605.6-520345) at the position(16 h m s , − ◦ ′ ′′ ′′ (Stephen et al. 2005). Recently,the position has been refined by Swift observations at(16 h m s , − ◦ ′ ′′
18) with a 3. ′′
52 error circle radius(Malizia et al. 2007).We performed accurate astrometry of the field, shown inFigure 2, and find that there is a bright 2MASS object inside the3. ′′ Swift error circle. The NIR magnitudes of this object aregiven in Table 4. This object is clearly extended on the NIR im-ages, suggesting an extragalactic source. This is in agreementwith the result from Masetti et al. (2006), who showed that thisobject is a Seyfert 1.2 AGN at a redshift of 0.054, exhibitingH β and O iii emission lines. . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 11
IGR J17091-3624 was discovered at the position (RADEC J2000.0) = (17 h m , − ◦ ′ ′′ ), uncertainty ∼ ′ (Kuulkers et al. 2003). Follow-up analysis of archival datafrom the TTM telescope aboard the KVANT module of theMIR orbital station revealed that this source had been detectedin several observations performed on Oct.1-10, 1994, at theposition (RA DEC J2000.0) = (17 h m s , − ◦ ′ ′′ ), er-ror radius about 0.8 ′ . This TTM position is within 0.6 ′ of the INTEGRAL position (Revnivtsev et al. 2003a). It is also coin-cident with the SAX source 1SAX J1709-36. A variable ra-dio counterpart has been detected in follow-up radio obser-vations at the position (17 h m s ± . , − ◦ ′ ′′ ), giv-ing an error circle of 5 ′′ radius (Rupen et al. 2003). Sincethis source exhibited some radio emission it has been classi-fied as a galactic X-ray binary, and a candidate microquasar,probably hosting a black hole. It exhibits a large variabilityin X-rays, and it is uncertain if this source is a Be / X-ray bi-nary or an LMXB. Capitanio et al. (2006) confirm the lowabsorption ( N H ≤ × cm − ) and Comptonised spec-trum of this source. Negueruela & Schurch (2007) proposedthe 2MASS J17090199-3623260 source as a candidate coun-terpart, based on photometric catalogues. They report that thisobject is a late F8 V companion star. However, a more accu-rate position has been obtained by Kennea & Capitanio (2007):(RA DEC J2000.0) = (17 h m s , − ◦ ′ ′′ ′′
6, which excludes the association of the high energysource with the radio source.We have performed accurate astrometry of the field, shownin Figure 2, and we overplot the 3. ′′ Swift error circle. Wefind that the claimed counterpart 2MASS J17090199-3623260of Negueruela & Schurch (2007) is well outside this error cir-cle; we can therefore reject it. We report the discovery of twoblended candidate counterparts inside the error circle, labeled1 and 2 in Figure 2 respectively, located at 0. ′′ ′′ . µ m). We can therefore not firmly con-clude the nature of this binary system. However, it is interest-ing to note that the R ∗ / D ∗
90% best fit values are very low( = . × − ). From these values we can compute the rangeof maximal radius that the massive star would have if it wasat the maximal distance inside our Galaxy, at D ∗ =
30 kpc:we find R ∗ max = [6 . − . R ⊙ . Since the maximal radius ofthe companion star would be ∼ R ⊙ , this star cannot be ei-ther a supergiant, or a giant. Alternatively, it could be a mainsequence early-type star, but then located very far away in ourGalaxy. We therefore conclude that this object is more probablyan LMXB system in the Galactic bulge. IGR J17252-3616 was discovered on 2004 February 9 inthe Galactic bulge region, at the position (17 h m , − ◦ ′ )by Walter et al. (2004a). Observations performed by XMM-Newton on 2004 March 21 by Zurita Heras et al. (2006) lo-calized the source at (17 h m s , − ◦ ′ ′′
6) with 4 ′′ ac-curacy. This source is a rediscovery of the EXOSAT sourceEXO 1722-363, based on similar timing and spectral prop-erties. It has been shown to be a heavily absorbed ( N H ∼ . × cm − ) and persistent source, exhibiting apparenttotal eclipses, and a hard X-ray spectrum with either an ab-sorbed Compton (kT ∼ τ ∼ .
8) or a flat powerlaw ( Γ ∼ . α line at6.4 keV. The detection of a spin period of ∼ . ∼ .
72 days securely classified this source as abinary X-ray Pulsar (Zurita Heras et al. 2006). Thompson et al.(2007) refined the orbital period to P = . . M ⊙ , suggesting an HMXB na-ture. In addition, we point out that putting the spin and orbitalperiods of this source on a Corbet diagram (Corbet 1986) al-lows us to suggest a supergiant HMXB nature.We performed accurate astrometry of the source, and over-plot the XMM-Newton error circle, as shown in Figure 2. Thereis a bright 2MASS counterpart, 2MASS J17251139-3616575(K S = ′′ XMM-Newton error circle, labelled 2 to 4. Allthese candidates are located at 0.7, 1.4, 3.7 and 3. ′′ i and He ii lines with likely P-Cygni profiles at2 . µ m, and perhaps Fe ii . From these NIR spectra, typical ofan OB star, we conclude that the companion star of this sourcehas an OB spectral type. Furthermore, the presence of He i inabsorption and with P-Cygni profile constrains the spectral typeto a B supergiant (Hanson et al. 2005). This result is in agree-ment with the suggestion by Zurita Heras et al. (2006), basedon the presence of this bright 2MASS source in the error cir-cle. This source is therefore an HMXB system, probably host-ing a supergiant companion star, in agreement with the resultsby Thompson et al. (2007), and in agreement with its positionin the Corbet diagram. The SED, consistent with the HMXBnature of the system, is shown in Figure 1. IGR J17391-3021 was discovered on 2003 August 26 at theposition (RA DEC J2000.0) = (17 h m , − ◦ ′
5) with a / NIR observations revealing the obscured
INTEGRAL binary systems ′ uncertainty by Sunyaev et al. (2003). Chandra observa-tions performed on 2003 October 15 localized the source at(17 h m s , − ◦ ′ ′′
6) with ∼ ′′ accuracy (Smith et al.2006). It is a rediscovery of a previously known ASCA and
Rossi-XTE source AX J1739.1-3020 = XTE J1739-302(Smith 2004). Negueruela et al. (2006a) have suggested thatthe optical counterpart of IGR J17391-3021 is a USNO A2.0source (USNO B1.0 0596-058586) with B =
17 and R = = . ± . = . ± .
027 and K S = . ± . INTEGRAL data, with flares lasting between 30 minand 3 hours (Sguera et al. 2005), the bright ones reaching330 mCrab (T¨urler et al. 2007). Negueruela et al. (2006a) statethat this source is most likely an HMXB, however the outburstsare shorter than expected for HMXBs or Be / NS binaries, con-sistent with the SFXTs.We performed accurate astrometry of the field (rms offit = ′′ Chandra error circle, as shown inFigure 2. Optical and NIR magnitudes of the candidate counter-part are given in Tables 2 and 4 respectively. However the NIRmagnitudes are out of the domain of linearity of SofI, whichexplains the discrepancy with the 2MASS magnitudes. We findthat this 2MASS source is a blended source, however from theastrometry, it is clear that the 1 ′′ Chandra error circle confirmsthat the 2MASS source is the counterpart of this source.We examine the optical and NIR spectra shown in Figure 5.We report the detected lines in Table 8. In the optical spectrum,we first detect interstellar lines at 5800, 5890-6 (Na I doublet),H α , H lines (Paschen), He i and He ii emission lines, N I lines.The NIR spectrum is very rich in H lines from the Paschenand Brackett series, and also in He i and He ii emission lines,some exhibiting P-Cygni profiles, and O i lines. All these linesare characteristic of early-type stars, more precisely of a super-giant O star, in agreement with the O8Iab(f) spectral type de-rived by Negueruela et al. (2006a). IGR J17391-3021 is there-fore a supergiant HMXB, located at a distance of ∼ . I doublet = = . × W (Å) = .
25 magnitudes (using Munari & Zwitter(1997)); N (H i + H = . × × E ( B − V ) = . × atoms / cm (using Bohlin et al. 1978), the column densityis consistent with the one indicated in Table 7. IGR J17597-2201 was discovered at the position (RA DECJ2000.0) = (17 h m , − ◦ ′ ) with ∼ ′ uncertainty(Lutovinov et al. 2003). XMM-Newton observations localized the source at (17 h m s , − ◦ ′ ′′ ) with a 4 ′′ accuracy(Walter et al. 2006). It exhibits an absorption of N H = . ± . × cm − , or 2 . ± . × cm − when a partial-covering absorber is included. This source, associated withthe Rossi-XTE source XTE J1759-220, is a Low-Mass X-rayBinary system, a late-type transient type I X-ray burster, there-fore hosting a neutron star, with a dipping behavior of ∼ ∼ ′′ XMM-Newton error circle (labeled 1, 3 and 5 and located respectivelyat 2.25, 0.95 and 2. ′′
05 from the centre of the
XMM-Newton error circle). In addition, there are one faint and one brightcandidate counterparts, lying on the error circle (labeled 2 and4, and located respectively at 3.8 and 3. ′′ XMM-Newton error circle). We give the NIR magnitudes ofthese candidate counterparts in Table 4. Since the previouslyproposed counterpart is outside the error circle, and since wepropose new candidate counterparts, this source deserves fur-ther observations to find which one is the right counterpart.By fitting the SED of the brightest candidate labeled 1,which is also the closest to the error circle centre, with themodel described in Section 2.4, we obtain a stellar temperature T ∗ = R ⊙ , andtaking a mean R ∗ / D ∗ of 2 × − , we obtain a distance of35 . R ∗ = R ⊙ typical of a B V companion star, we derive a dis-tance of D ∗ = . IGR J18027-2016 was discovered at the position (RA DECJ2000.0) = (18 h m s , − ◦ ′
3) (Revnivtsev et al. 2004).
XMM-Newton observations allowed to localize the sourceat (18 h m s , − ◦ ′ ′′ ) with 4 ′′ accuracy (Walter et al.2006). The source was originally called IGR J18029-2016, andit is associated with the SAX source SAX J18027-2017. Theabsorption is N H = . ± . × cm − (Walter et al. 2006). Itis an X-ray pulsar, and a transient source, an eclipsing HMXB,likely at a distance of 10 kpc. An orbital period of 4.57 days anda pulse period of 139.47 s were reported by Hill et al. (2005).These authors have derived the system parameters, with an ex- . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 13 centricity of e ≤ .
2, a mass function of f(M) ∼ ± M ⊙ ,implying a mass of the companion of 18 . − . M ⊙ .We performed accurate astrometry of this source (rms offit = ′′ ∼ ′′ from the centre ofthe XMM-Newton error circle, which is the candidate counter-part proposed by Walter et al. (2006). However there is anotherbright source well inside the error circle, labeled Candidate 2.There is also at least one faint counterpart inside the error cir-cle. We give the NIR magnitudes of Candidate 1 and Candidate2 in Table 4. Based on the proximity to the error circle centre,and its NIR brightness, we favour Candidate 1 as the likelycandidate.The optical and NIR spectra of Candidate 1 are shown inFigure 5. We report the detected lines in Table 8. In the opticalspectrum we detect hydrogen ( α to ζ ) and He ii emission lines,and in the NIR spectrum we detect H (Paschen and Brackett se-ries), He i and He ii emission lines, some tentatively exhibitingP-Cygni profiles. These NIR spectra are typical of a supergiantOB star, which is therefore likely the spectral type of the com-panion star: IGR J18027-2016 is therefore a supergiant HMXBsystem. Fitting the data with the model described in Section2.4, we obtain a stellar temperature T ∗ = R ∗ / D ∗ minimizing χ (3 . × − ), and assuming a typical ra-dius of a B supergiant star, i.e. R ∗ = R ⊙ , we derive a distanceof D ∗ = . IGR J18483-0311 was discovered at the position (RA DECJ2000.0) = (18 h m , − ◦ ′ ), with uncertainty ∼ ′ (Chernyakova et al. 2003). The Swift observations allowedSguera et al. (2007) to refine the position of the source to(18 h m s , − ◦ ′ ′′ ′′
3. The
Swift re-fined position allowed them to identify an optical counter-part from the USNO-B1.0 and 2MASS catalogue locatedat (18 h m s , − ◦ ′ ′′
5) with magnitudes R = = = = = N H = × cm − , a Γ = . ff at E cut =
22 keV (Sguera et al. 2007). Timing analysisof
Rossi-XTE / ASM light curve have allowed investigators toderive an orbital period of 18 . ± .
05 days (Levine & Corbet2006). Sguera et al. (2007) also report that the source contains apulsar with a spin period of 21 . ± . ± = ′′ Swift error circle,which is the candidate counterpart proposed by Sguera et al.(2007). However this source seems to be blended with anotherfainter source, at 2.5 ′′ from the centre of the error circle. Wegive the NIR magnitudes of the bright candidate counterpart inTable 4.Fitting the SED of this counterpart with the model de-scribed in Section 2.4 allows us to derive a stellar temperatureof T ∗ = χ , which is typicalof a B star. The other parameters are given in Table 6, and theSED is shown in Figure 1. The stellar temperature is consis-tent with a B spectral type companion star. Since the R ∗ / D ∗ ratio minimizing χ is 2 . × − , the distance of this sourcewould then be 0.9 kpc if the companion star is a main sequencestar (with a typical stellar radius of R ∗ = R ⊙ ), 1.5 kpc for asub-giant and 2.7 kpc for a supergiant star (with a typical stel-lar radius of R ∗ = R ⊙ ). This source exhibits a strong NIRexcess, which might indicate the presence of a disk / wind suchas in massive stars. Furthermore, its position in the Corbet dia-gram is between Be and wind accretor-supergiant X-ray binarysystems. Although we cannot firmly conclude on the spectraltype and class, this SED shows that this source is an HMXBsystem. IGR J19140 + = (19 h m s , + ◦ ′ ′ ) by Hannikainen et al. (2003). Chandra ob-servations performed on 2004 May 11 localized thesource at (19 h m s , + ◦ ′ ′′
29) with 0. ′′ Rossi-XTE observations allowed investigators to derive a Γ ∼ . N H ∼ × cm − (Swank & Markwardt 2003) withvariations of N H up to ∼ cm − (Rodriguez et al. 2005).An orbital period of 13 .
55 days was found from timing anal-ysis of
Rossi-XTE data, with an X-ray activity detected with
Rossi-XTE / ASM as early as 1996 (Corbet et al. 2004), confirm-ing the binary nature of the source. Rodriguez et al. (2005),after a comprehensive analysis of
INTEGRAL and
Rossi-XTE data, showed that the source was spending most of its timein a faint state but reported high variations of luminosity andabsorption column density. It is a persistent HMXB with evi-dence for the compact object being a neutron star rather thana black hole, exhibiting a variable absorption column density,and a bright iron line (Rodriguez et al. 2005). This source hasother names: IGR J19140 +
098 (Hannikainen et al. 2003), andEXO 1912 + + = = S = .
06 magnitude).We performed accurate astrometry of the field (rms offit = ′′ + ′′ + S = .
27 magnitude). We give the NIR magnitudes of the deblendedcandidate counterpart in Table 4. These deblended magni- / NIR observations revealing the obscured
INTEGRAL binary systems tudes we derive are di ff erent from the magnitudes given in the2MASS catalogue, because both 2MASS sources are spatiallyvery close in the 2MASS data.We show the NIR spectra of this source in Figure 4. We re-port the detected lines in Table 8. The spectrum is dominated byH (Paschen and Brackett series), and He i and He ii in emission.The NIR spectra are typical of an OB spectral type companionstar, and the narrowness of the lines suggests a supergiant type,which is consistent with the results by Nespoli et al. (2007)for a B1I stellar type companion, derived from spectra ob-tained at ESO / NTT / SofI. This classification has been refined toB0.5I based on spectra obtained at UKIRT (Hannikainen et al.2007), making IGR J19140 + + µ m found in the Midcourse Space Experiment( MSX , Mill 1994), however Rahoui et al. (2008) show thatin’t Zand et al. (2006) are in fact reporting the summed flux ofa blended source, composed of the MIR counterparts of bothIGR J19140 + + +
4. Discussion
We begin this Section by giving a summary of the results ofall individual sources. We continue by showing the large scaleenvironment of these sources, and report the presence of ab-sorption in their environment. We then recall the general char-acteristics of HMXBs, before discussing the results obtained,in the context of the
INTEGRAL era.
We found by spectroscopy of the most likely candidate coun-terparts the spectral types of IGR J16320-4751, IGR J16358-4726, IGR J16479-4514, IGR J17252-3616 and IGR J18027-2016: they are all of supergiant OB types, IGR J16358-4726likely hosting a sgB[e] companion star. We also confirm thesupergiant O nature of IGR J17391-3021, and the supergiantB nature of IGR J19140 + INTEGRAL sources. We give the results of the column densityin optical / IR, spectral type of the companion stars, and type of sources for all individual sources of our sample. We also giveall the parameters known about these sources, such as the spinand orbital period, and column density derived from X-ray ob-servations, in order to facilitate the following discussion. Theinterstellar column density and absorption in the optical andNIR domain have been derived from our observations, given inTable 6 for the sources IGR J16393-4643, IGR J16418-4532,IGR J17091-3624, IGR J17597-2201, IGR J18027-2016 andIGR J18483-0535, and in Rahoui et al. (2008) for the remain-ing sources. We then converted the column density into absorp-tion in magnitudes, using the relation given in Cardelli et al.(1989): N H / A v = . × cm − / magnitudes.The results, concerning the spectral type of the companionstar, given by these SED fittings are in agreement with those di-rectly derived from spectroscopy, when available. On the otherhand, they allow us to derive the likely spectral type of the com-panion star, when there is no spectroscopic information. We cantherefore conclude that most of these obscured sources host lu-minous, massive, hot and early-type companion stars, i.e. ofOB spectral type, most of them being evolved stars of the su-pergiant spectral class.From these SEDs, all reported in Figure 1, we candirectly compare the optical to MIR with the hard X-ray domain integrated flux (corresponding to the energyoutput). All sources for which both fluxes are compara-ble are supergiant HMXBs: IGR J16418-4532, IGR J16479-4514, IGR J17252-3616, IGR J17391-3021, IGR J18027-2016,IGR J19140 + Four sources of the studied sample exhibit large-scale regionsof absorption in the NIR images, very close to the line of sightof the hard X-ray source: IGR J16358-4726, IGR J16418-4532,IGR J16479-4514 and IGR J17391-3021. We show in Figure 6the large field J band image of these sources (except forIGR J16479-4514 for which we show the large field K S bandimage). This absorption region might be due to the presenceof extended molecular clouds and / or H ii regions. The presenceof such highly absorbed regions is not surprising close to thesepeculiar hard X-ray sources, since they must be strongly linkedto their formation. For instance, the Norma arm region is oneof the richest star-forming regions of our Galaxy, where manyhigh-mass stars form and evolve (Bronfman et al. 1996). Thereexists therefore a high probability for binary systems made up . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 15
Fig. 4.
From top to bottom, and left to right: combined blue and red grism NIR spectra of IGR J16320-4751 (Candidate 1),IGR J16358-4726, IGR J16479-4514 (Candidate 1) and IGR J19140 + INTEGRAL –for which the dis-tance is known– and of star-forming complexes, mainly OB regions reported by Russeil (2003). They have shown that theirspatial distribution is similar, suggesting that HMXBs are as-sociated with these complexes. The discovery of large-scaleabsorption regions in the direction of these sources is there-fore not surprising, since the formation sites of HMXBs areclosely linked to rich star forming regions. Indeed, the shortlife of HMXBs prevents these systems from migrating far awayfrom their birthplace. Characterisation of these large-scale ab- / NIR observations revealing the obscured
INTEGRAL binary systems
Fig. 5.
Top panel: Combined flux calibrated spectra of the two sources IGR J17252-3616 Candidate 1 (left) and IGR J18027-2016 (right) respectively. The optical spectra were obtained with 3.6m / EFOSC, and the blue and red grism NIR spectra withNTT / SofI. We combined EFOSC2 and SofI spectra by applying a scaling factor of 18.4035 for IGR J17252-3616 and 2.417 forIGR J18027-2016, the di ff erence being due to a di ff erent calibration between EFOSC2 and SofI, and to di ff erent exposure times.These two factors were obtained by dividing the flux in the overlap region between EFOSC2 and SofI spectra. The spectra areextremely red because of the galactic reddening. Besides the low S / N of the spectra, a number of narrow absorption lines couldbe detected. The y axis of the spectra are given in ” λ F λ ” units: erg s − cm − .Bottom left panel: IGR J17391-3021 flux calibrated optical spectrum, with the y axis given in ” λ F λ ” units: erg s − cm − . Bottomright panel: combined blue and red grism NIR spectra of IGR J17391-3021, with the y axis in arbitrary units. . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 17
Table 7.
Summary of results and characteristics of our studied sample of
INTEGRAL sources. We give the name of the sources,the region of the Galaxy in the direction in which they are located, their spin and orbital period, the interstellar column density( N H I), the absorption derived from optical to infrared observations ( N H IR), the absorption derived from X-ray observations( N H X), the spectral type (SpT) of their most likely candidate obtained or confirmed by spectroscopy (spec) or by fitting theSED (sed), the nature and type of the binary system, and the reference (Ref) to the spectral type. More details on each sourceare given in Section 3. Details on how we obtained N H I, N H IR and N H X are given in Section 2.4. Type abbreviations: AGN = Active Galactic Nucleus, B = Burster (neutron star), BHC = Black Hole Candidate, D = Dipping source, LMXB = Low-MassX-ray Binary, HMXB = High-Mass X-ray Binary System, OBS = obscured source, SFXT = Supergiant Fast X-ray Transient,T: Transient source, XP: X-ray Pulsar. The classification as SFXT is still subjective, since we lack some accurate observationson a long-term scale for most of the sources. The spectral types come from optical / NIR spectroscopy, reported in the referencesgiven in the column Ref. c: this paper, h: Hannikainen et al. (2007), m: Masetti et al. (2006), neg: Negueruela et al. (2006a), nes:Nespoli et al. (2007).
Source Region Pspin Porb N H I N H IR N H X SpT Nature Ref(s) (d) 10 cm − cm − cm − IGR J16320-4751 Norma 1250 8.96(1) 2.14 6.6 21 spec: sgO HMXB / XP / T / OBS cIGR J16358-4726 Norma 5880 2.20 3.3 33 spec: sgB[e]? HMXB / XP / T / OBS cIGR J16393-4643 Norma 912 3.6875(6) 2.19 2.19 24.98 sed: BIV-V? HMXB / XP / T cIGR J16418-4532 Norma 1246 3.753(4) 1.88 2.7 10 sed: sgOB? HMXB / XP / SFXT cIGR J16479-4514 Norma 2.14 3.4 7.7 spec: sgOB HMXB / SFXT? cIGR J16558-5203 - - - - - - AGN Seyfert 1.2 mIGR J17091-3624 GC 0.77 1.03 1.0 sed: LMXB BHC cIGR J17252-3616 GC 413 9.74(4) 1.56 3.8 15 spec: sgB HMXB / XP / OBS cIGR J17391-3021 GC 1.37 1.7 29.98 spec: O8Iab(f) HMXB / SFXT / OBS negIGR J17597-2201 GC 1.17 2.84 4.50 sed: LMXB LMXB / B / D / P cIGR J18027-2016 GC 139 4.5696(9) 1.04 1.53 9.05 spec: sgOB HMXB / XP / T cIGR J18483-0311 GC 21 .
05 18.55 1.62 2.45 27.69 sed: HMXB? HMXB / XP cIGR J19140 + / OBS h, nes sorption regions, and measurement of the metallicity of starshosted by these regions are required to clarify this situation.
INTEGRAL era
HMXBs are separated in two distinct groups. The first groupcontains the majority of the HMXB systems, constituted ofknown or suspected Be / X-ray Binary systems (BeXBs), calledBe / X-ray transients. In Be systems, the donor is a Be star andthe compact object is a neutron star typically in a wide, mod-erately eccentric orbit, spending little time in close proximityto the dense circumstellar disk surrounding the Be companion(Coe 2000; Negueruela 2004). X-ray outbursts occur when thecompact object passes through the Be-star disk, accreting fromthe low-velocity and high-density wind around Be stars, andexhibiting hard X-ray spectra.The second group of HMXB systems contains theSupergiant / X-ray Binaries (SXBs), where the compact objectorbits deep inside the highly supersonic wind of a super-giant early-type star, which plays the role of the donor star(Kaper et al. 2004). The X-ray luminosity is powered either byaccretion from the strong stellar wind of the optical compan-ion, or by Roche-lobe overflow. In a wind-fed system, accretionfrom the stellar wind results in a persistent X-ray luminosity of 10 − erg / s, while in a Roche-lobe overflow system, matterflows via the inner Lagrangian point to form an accretion disc.In this case, a much higher X-ray luminosity ( ∼ erg / s) isthen produced during the outbursts.In the pre- INTEGRAL era, known HMXBs were mostlyBeXBs systems. For instance, in the catalogue of HMXBs ofLiu et al. (2000), there were 54 BeXBs and 7 SXBs identified,out of 130 HMXBs, representing a proportion of 42% and 5%respectively. Then, between the two last editions of HMXB cat-alogues (Liu et al. 2000 and Liu et al. 2006), the proportion ofSXBs compared to BeXBs has increased, with the first HMXBsidentified in the
INTEGRAL data. The third IBIS / ISGRI soft γ -ray survey catalogue (Bird et al. 2007), spanning nearly 3.5years of operations, contains 421 sources detected with the INTEGRAL observatory, of which 214 ( ∼
50 %) were discov-ered by this satellite. This catalogue, extending up to 100 keV,includes 118 AGNs, 147 X-ray binaries (79 LMXBs and 68HMXBs), 23 Cataclysmic Variables, 23 other objects, and 115still unidentified objects. Among the 68 HMXBs, 24 have beenidentified as BeXBs and 19 as SXBs, representing a proportionof 35% and 28% respectively. The proportion of BeXBs, rela-tive to the total of HMXBs, has decreased by a factor 1.2 whilethe proportion of SXBs has increased by a factor 5.6 betweenthe catalogue of Liu et al. (2000) and the one of Bird et al. / NIR observations revealing the obscured
INTEGRAL binary systems (2007). Related to this increasing proportion of SXBs, the otherhighlight of the
INTEGRAL catalogue is the emergence of theSFXT class, with 12
INTEGRAL sources being firm or possiblecandidates.Our studied sample of
INTEGRAL sources allows us toadd four newly identified SXBs which were not classifiedas such in Bird et al. (2007): IGR J16320-4751, IGR J16358-4726, IGR J17252-3616 and IGR J18027-2016. The othersources that we have identified in this paper as supergiantswere already considered SXBs, based either on spectral clas-sification –IGR J17391-3021 and IGR J19140 + INTEGRAL has drastically changed the statistical situation concerning thenature of HMXBs, by revealing a new dominant population ofsupergiant X-ray binaries, which are purely wind accretor sys-tems.Although this came as a surprise, it is a posteri-ori consistent with the fact that these hard X-ray emit-ters are sources ideally detected by
INTEGRAL , as dis-cussed in Lutovinov et al. (2005a), Dean et al. (2005) andBodaghee et al. (2007).
INTEGRAL , observing at energieshigher than the threshold above which photoelectric absorp-tion becomes negligible in most matter, can easily detect brightsources above a few tens of keV, while they are not detectablebelow, and therefore had remained hidden up to now. HMXBsaccreting by stellar wind create a naturally dense and highlyabsorbing circumstellar wind compared to Roche lobe over-flow in LMXBs, hiding the X-ray emission in a similar wayto Seyfert 2 AGNs (Dean et al. 2005; Malizia et al. 2003).
INTEGRAL
HMXBs
Let us now consider our results, summarized and put togetherwith other characteristics of these sources in Table 7. In thissample of 13
INTEGRAL sources, concentrated both towardsthe direction of the Norma arm and the Galactic centre, weclassified 10 HMXBs (8 sources hosting sgOB and 2 sourceshosting BIV-V companion stars), 2 LMXBs and 1 AGN. Weclearly confirm the predominance of HMXBs hosting super-giants, as opposed to those hosting Be companion stars: in oursample, 80% of HMXBs host compact objects (probably neu-tron stars) orbiting around OB supergiant secondaries. As al-ready discussed, this result is in agreement with the increaseof SXBs in the HMXBs population. However, quantitatively,the proportion of SXBs in our studied sample is higher thanin the Bird et al. (2007) catalogue. There are two reasons: first,our sample is much more limited; second, most of the sourcesof our sample are in the direction of the Norma arm, whichis associated with rich star-forming regions, the natural birth-place of massive stars, as discussed in Section 4.2. Most ofthese new
INTEGRAL sources are wind accretors, consistentwith their location in the Corbet diagram (Corbet 1986): nearlyall of the HMXBs discovered by
INTEGRAL , for which bothspin and orbital periods have been measured, are located in the upper part of this diagram, among other wind accretors, typicalof supergiant HMXBs. These systems exhibit extra absorptionby a factor of ∼ INTEGRAL sources ex-hibit a MIR excess, due to an absorbing component enshroud-ing the whole binary system. The MIR emission of the remain-ing sources comes from the supergiant companion star, show-ing that absorbing material is enshrouding the compact objectfor most of the sources (preliminary results of this paper weredescribed in Chaty & Rahoui 2006). We are therefore observ-ing two classes of
INTEGRAL sources, i.e. highly absorbedsources such as IGR J16358-4726, for which the extreme repre-sentant is IGR J16318-4848, and SFXTs such as IGR J17391-3021, for which the archetype is IGR J17544-2619.As shown in Table 7, these classes share similar proper-ties –for instance they both host supergiant companion stars–however they do not seem to have exactly the same configura-tion, and one way to explain their di ff erent characteristics canbe found in their excess in absorption, which does not seemto have the same origin. It is caused by two di ff erent phenom-ena in the case of the highly absorbed sources: the observa-tions from hard X-ray to MIR domains suggest the presenceof absorbing material concentrated around the compact object,and also some dust and / or cold gas, perhaps forming a cocoon,enshrouding the whole binary system (Filliatre & Chaty 2004;Rahoui et al. 2008). Their characteristics might be explainedby the presence of a compact object (neutron star or blackhole) orbiting within the dense wind surrounding the compan-ion star. On the other hand, in the case of SFXTs, characterisedby fast X-ray outbursts, the presence of the absorbing mate-rial seems concentrated around the compact object only, andMIR observations show that there is no need for any other ab-sorbing material around the whole system (Rahoui et al. 2008).Their characteristics might be explained by the presence of acompact object (neutron star or black hole) located on an ec-centric orbit around the companion star, and it would then bewhen the compact object penetrates the clumpy circumstellarenvelope that outbursts are caused. However the situation ismore complicated, since some SFXT sources are also highlyobscured, and the intrinsic absorption derived from X-ray ob-servations vary for some INTEGRAL sources (see e.g. the caseof IGR J19140 + . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 19 eral properties of these systems, we will need to better char-acterise the dust, its temperature, composition, geometry, ex-tension around the system, and to investigate where this dustor cold gas comes from. Finally, probably the most importantquestion to solve is whether this unusual circumstellar environ-ment is due to stellar evolution OR to the binary system itself.To answer this question, this dominant population of supergiantHMXBs now needs to be taken into account in population syn-thesis models.
5. Conclusions
We have performed an extensive study of a sample of 13
INTEGRAL sources, through optical and NIR photometry andspectroscopy, performing for each source accurate astrometry,identifying candidate counterparts, deriving their optical andNIR magnitudes, and obtaining spectra for most of them. Inaddition, we built and fitted the SED of these sources, fromMIR to hard X-rays. We thus identified the nature of the com-panion stars and of the binary systems by spectroscopy for 7of these sources, and by fitting their SED for 5 of them. We fi-nally reported NIR fields of four of these sources, which exhibitlarge-scale regions of absorption, probably linked to their for-mation process. We then discussed the existence of this dom-inant population of supergiant HMXBs in our Galaxy, bornwith two very massive components: a population which onlyrecently has been revealed by the
INTEGRAL observatory.Thus, it clearly appears that a study of this new popula-tion of supergiant HMXBs, constraining the nature and orbitalparameters of these systems, and linking them to populationsynthesis models, will provide a better understanding of theevolution of HMXBs. These systems are probably the primaryprogenitors of neutron star / neutron star or neutron star / blackhole mergers. There is therefore the possibility that they arerelated to short / hard γ -ray bursts, and also that they might begood candidates for gravitational wave emitters. Because mostof these sources are obscured, the ”Norma arm”-like sourcescan only be studied in the hard X-ray and infrared domains. Ajoint study of these sources with multi-wavelength hard X-ray,optical, NIR, MIR (and radio) observations is therefore neces-sary. Acknowledgements.
Based on observations collected at the EuropeanOrganisation for Astronomical Research in the Southern Hemisphere,Chile (ESO Programme 073.D-0339). We acknowledge Jorge Melnickfor special DDT time at 3.6 telescope on EFOSC2. SC thanks theESO sta ff and especially Valenti Ivanov and Emanuela Pompei fortheir invaluable assistance during the run when we performed theseoptical and NIR observations. JAT acknowledges partial supportfrom Chandra award number GO5-6037X issued by the
ChandraX-Ray Observatory Center , which is operated by the SmithsonianAstrophysical Observatory for and on behalf of the NationalAeronautics and Space Administration (NASA), under contractNAS8-03060. This research has made use of NASA’s AstrophysicsData System, of the SIMBAD database, operated at CDS, Strasbourg,France, and of data products from the Two Micron All Sky Survey,which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center / California Instituteof Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.
References
Bird, A. J., Barlow, E. J., Bassani, L., et al. 2006, ApJ, 636,765Bird, A. J., Malizia, A., Bazzano, A., et al. 2007, ApJS, 170,175Bodaghee, A., Courvoisier, T. J.-L., Rodriguez, J., et al. 2007,A&A, 467, 585Bodaghee, A., Walter, R., Zurita Heras, J. A., et al. 2006, A&A,447, 1027Bohlin, R. C., Savage, B. D., & Drake, J. F. 1978, ApJ, 224,132Bronfman, L., Nyman, L.-A., & May, J. 1996, A&AS, 115, 81Capitanio, F., Bazzano, A., Ubertini, P., et al. 2006, ApJ, 643,376Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345,245Caron, G., Mo ff at, A. F. J., St-Louis, N., Wade, G. A., & Lester,J. B. 2003, AJ, 126, 1415Chaty, S. & Filliatre, P. 2005, Ap&SS, 297, 235Chaty, S. & Rahoui, F. 2006, in The Obscured Universe, Procs.of 6th INTEGRAL workshop, Moscow, Russia, July 2-8,2006, to be published by ESA’s Publications Division inDecember 2006 as Special Publication SP-622, in press(astro-ph / + Corbet, R., Barbier, L., Barthelmy, S., et al. 2006, TheAstronomer’s Telegram, 779, 1Corbet, R., Barbier, L., Barthelmy, S., et al. 2005, TheAstronomer’s Telegram, 649, 1Corbet, R. H. D. 1986, MNRAS, 220, 1047Corbet, R. H. D., Hannikainen, D. C., & Remillard, R. 2004,The Astronomer’s Telegram, 269, 1Dean, A. J., Bazzano, A., Hill, A. B., et al. 2005, A&A, 443,485Dickey, J. M. & Lockman, F. J. 1990, ARA&A, 28, 215Filliatre, P. & Chaty, S. 2004, ApJ, 616, 469Hannikainen, D. C., Rawlings, M. G., Muhli, P., et al. 2007,MNRAS, 380, 665Hannikainen, D. C., Rodriguez, J., & Pottschmidt, K. 2003,IAU Circ., 8088, 4Hanson, M. M., Kudritzki, R.-P., Kenworthy, M. A., Puls, J., &Tokunaga, A. T. 2005, ApJS, 161, 154Hill, A. B., Walter, R., Knigge, C., et al. 2005, A&A, 439, 255in’t Zand, J. J. M., Jonker, P. G., Nelemans, G., Steeghs, D., &O’Brien, K. 2006, A&A, 448, 1101Kaper, L., van der Meer, A., & Tijani, A. H. 2004, in RevistaMexicana de Astronomia y Astrofisica Conference Series,ed. C. Allen & C. Scarfe, 128–131Kennea, J. A. & Capitanio, F. 2007, The Astronomer’sTelegram, 1140, 1Kouveliotou, C., Patel, S., Tennant, A., et al. 2003, IAU Circ.,8109, 2Kuulkers, E., Lutovinov, A., Parmar, A., et al. 2003, The / NIR observations revealing the obscured
INTEGRAL binary systems(a) IGR J16358-4726 (b) IGR J16418-4532(c) IGR J16479-4514 (d) IGR J17391-3021
Fig. 6.
Large fields of 4 studied sources exhibiting high absorption along their line of sight. Size: 5 . ′ × . ′ ; North is to the topand East to the left. We overplot a white circle to indicate the position of the INTEGRAL sources.Astronomer’s Telegram, 149, 1Landolt, A. U. 1992, AJ, 104, 340Lebrun, F., Leray, J. P., Lavocat, P., et al. 2003, A&A, 411,L141Levine, A. M. & Corbet, R. 2006, The Astronomer’s Telegram,940, 1Liu, Q. Z., van Paradijs, J., & van den Heuvel, E. P. J. 2000,Astron. Astrophys. Suppl. Ser., 147, 25Liu, Q. Z., van Paradijs, J., & van den Heuvel, E. P. J. 2006,A&A, 455, 1165Lutovinov, A., Revnivtsev, M., Gilfanov, M., et al. 2005a,A&A, 444, 821Lutovinov, A., Rodriguez, J., Revnivtsev, M., & Shtykovskiy,P. 2005b, A&A, 433, L41Lutovinov, A., Walter, R., Belanger, G., et al. 2003, TheAstronomer’s Telegram, 155, 1Malizia, A., Bassani, L., di Cocco, G., et al. 2004, TheAstronomer’s Telegram, 227, 1Malizia, A., Bassani, L., Stephen, J. B., et al. 2003, ApJ, 589, L17Malizia, A., Landi, R., Bassani, L., et al. 2007, ApJ, 668, 81Markwardt, C. B. & Swank, J. H. 2003, The Astronomer’sTelegram, 156, 1Masetti, N., Morelli, L., Palazzi, E., et al. 2006, A&A, 459, 21Mill, J. D. 1994, in Proc. SPIE Vol. 2232, p. 200-216, SignalProcessing, Sensor Fusion, and Target Recognition III, IvanKadar; Vibeke Libby; Eds., ed. I. Kadar & V. Libby, 200–216Molkov, S., Mowlavi, N., Goldwurm, A., et al. 2003, TheAstronomer’s Telegram, 176, 1Munari, U. & Tomasella, L. 1999, A&AS, 137, 521Munari, U. & Zwitter, T. 1997, A&A, 318, 269Negueruela, I. 2004, in Revista Mexicana de Astronomia yAstrofisica Conference Series, ed. G. Tovmassian & E. Sion,55–56Negueruela, I. & Schurch, M. P. E. 2007, A&A, 461, 631Negueruela, I., Smith, D. M., Harrison, T. E., & Torrej´on, J. M.2006a, ApJ, 638, 982 . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 21
Negueruela, I., Smith, D. M., Reig, P., Chaty, S., & Torrej´on,J. M. 2006b, in ESA Special Publication, Vol. 604, ESASpecial Publication, ed. A. Wilson, 165–170Nespoli, E., Fabregat, J., & Mennickent, R. 2007, TheAstronomer’s Telegram, 982, 1Patel, S. K., Zurita, J., Del Santo, M., et al. 2007, ApJ, 657, 994Pellizza, L. J., Chaty, S., & Negueruela, I. 2006, A&A, 455,653Persson, S. E., Murphy, D. C., Krzeminski, W., Roth, M., &Rieke, M. J. 1998, AJ, 116, 2475Prat, L., Rodriguez, J., & Hannikainen, D. C. 2008, ArXiv e-prints, 801Predehl, P. & Schmitt, J. 1995, A&A, 293, 889Rahoui, F., Chaty, S., Lagage, P.-O., & Pantin, E. 2008, A&A,in pressRevnivtsev, M., Gilfanov, M., Churazov, E., & Sunyaev, R.2003a, The Astronomer’s Telegram, 150, 1Revnivtsev, M., Tuerler, M., Del Santo, M., et al. 2003b,IAU Circ., 8097, 2Revnivtsev, M. G., Sunyaev, R. A., Varshalovich, D. A., et al.2004, Astronomy Letters, 30, 382Rodriguez, J., Bodaghee, A., Kaaret, P., et al. 2006, MNRAS,366, 274Rodriguez, J., Cabanac, C., Hannikainen, D. C., et al. 2005,A&A, 432, 235Rodriguez, J., Tomsick, J. A., Foschini, L., et al. 2003, A&A,407, L41Rupen, M. P., Mioduszewski, A. J., & Dhawan, V. 2003, TheAstronomer’s Telegram, 152, 1Russeil, D. 2003, A&A, 397, 133Sguera, V., Barlow, E. J., Bird, A. J., et al. 2005, A&A, 444,221Sguera, V., Bazzano, A., Bird, A. J., et al. 2006, ApJ, 646, 452Sguera, V., Hill, A. B., Bird, A. J., et al. 2007, A&A, 467, 249Smith, D. M. 2004, The Astronomer’s Telegram, 338, 1Smith, D. M., Heindl, W. A., Markwardt, C. B., et al. 2006,ApJ, 638, 974Stephen, J. B., Bassani, L., Molina, M., et al. 2005, A&A, 432,L49Sunyaev, R., Lutovinov, A., Molkov, S., & Deluit, S. 2003, TheAstronomer’s Telegram, 181, 1Swank, J. H. & Markwardt, C. B. 2003, The Astronomer’sTelegram, 128, 1Tauris, T. M. & van den Heuvel, E. P. J. 2006, Formation andevolution of compact stellar X-ray sources (Compact stellarX-ray sources), 623–665Thompson, T. W. J., Tomsick, J. A., Rothschild, R. E., in’tZand, J. J. M., & Walter, R. 2006, ApJ, 649, 373Thompson, T. W. J., Tomsick, J. A., Zand, J. J. M. i.,Rothschild, R. E., & Walter, R. 2007, ApJ, 661, 447Tomsick, J. A., Chaty, S., Rodriguez, J., et al. 2006, ApJ, 647,1309Tomsick, J. A., Lingenfelter, R., Corbel, S., Goldwurm, A.,& Kaaret, P. 2004a, in ESA SP-552: 5th INTEGRALWorkshop on the INTEGRAL Universe, ed. V. Schoenfelder,G. Lichti, & C. Winkler, 413–416Tomsick, J. A., Lingenfelter, R., Corbel, S., Goldwurm, A., &Kaaret, P. 2004b, The Astronomer’s Telegram, 224, 1 Tomsick, J. A., Lingenfelter, R., Walter, R., et al. 2003,IAU Circ., 8076, 1T¨urler, M., Balman, S., Bazzano, A., et al. 2007, TheAstronomer’s Telegram, 1019, 1Walter, R., Bodaghee, A., Barlow, E. J., et al. 2004a, TheAstronomer’s Telegram, 229, 1Walter, R., Courvoisier, T. J.-L., Foschini, L., et al. 2004b,in ESA Special Publication, Vol. 552, 5th INTEGRALWorkshop on the INTEGRAL Universe, ed. V. Schoenfelder,G. Lichti, & C. Winkler, 417–422Walter, R., Zurita Heras, J., Bassani, L., et al. 2006, A&A, 453,133Zurita Heras, J. A., de Cesare, G., Walter, R., et al. 2006, A&A,448, 261 / NIR observations revealing the obscured
INTEGRAL binary systems
Table 8: Spectroscopy results. We indicate the name of the sources, theidentification of the lines, the rest wavelength ( µ m ), the fitted centralwavelength ( µ m ), the flux (in erg s − cm − for optical spectra and in ar-bitrary units for NIR spectra), the equivalent width (EQW in Å), and FullWidth Half Maximum (FWHM in Å). T stands for telluric.Source Identification λ λ fit Flux EQW FWHMIGR J16320-4751 Pa(7-3) 1.005 1.0052 1296.88 -3.773 ± ± / HeI 2.166 / ± . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 23
Table 8: continued.Source Identification λ λ fit
Flux EQW FWHM1.7891 -2371.63 2.32 20.62Br(8-4) 1.945 1.9475 8758.25 -6.548 92.961.9822 4953.06 -3.442 38.832.0076 -22693.7 15.46 192.72.0547 -4648.77 2.992 90.7HeI 2.1126 2.1117 -2376.81 1.379 30.27Br(7-4) / HeII 2.166 / + α / NIR observations revealing the obscured
INTEGRAL binary systems
Table 8: continued.Source Identification λ λ fit
Flux EQW FWHM0.8868 -4.96E-14 1.887 25.830.9006 -1.66E-13 6.293 49.690.9118 7.353E-15 -0.2933 17.460.9201 4.781E-14 -1.887 28.790.9230 -4.13E-14 1.545 22.380.9349 -5.66E-13 22.48 64.580.9423 -1.49E-12 57.2 309.80.9447 -2.00E-12 72.96 274.80.9504 -8.41E-13 32.56 178.7Pa(8-3) 0.954 0.9550 -1.19E-13 4.949 44.280.9712 1.268E-13 -4.463 36.450.9768 -2.08E-13 6.634 73.770.9930 7.416E-13 -25.57 218.41.0111 1.372E-14 -0.4479 13.331.0093 5.657E-14 -1.853 34.91Pa(7-3) / HeII 1.005 / / HeII 1.005 / / HeII 1.094 / / HeII 1.282 / + / HeII PCyg- 1.571 / + + / HeII 1.737 / + CIII 2.116 2.1157 11898.8 -1.87 28.88Br(7-4) / HeI 2.166 / ζ δ β ? 0.4861 0.4901 9.769E-16 -75.71 10.230.5180 -7.98E-16 51.37 9.9670.5460 2.099E-16 -7.693 12.53NaD 0.5890 0.5884 -1.99E-16 3.885 20.76 . Chaty et al.: Optical / NIR observations revealing the obscured
INTEGRAL binary systems 25
Table 8: continued.Source Identification λ λ fit
Flux EQW FWHM0.6251 3.172E-16 -5.072 42.17H α + ? 1.6060 46540.9 -1.455 7.072HeII? 1.6241 1.6220 -105641. 3.331 41.99Br(12-4)? PCyg- 1.641 1.6439 -340789. 10.27 82.88PCyg + + + / HeII 1.282 //