Faraday rotation measures of northern-hemisphere pulsars using CHIME/Pulsar
C. Ng, A. Pandhi, A. Naidu, E. Fonseca, V. M. Kaspi, K. W. Masui, R. Mckinven, A. Renard, P. Scholz, I. H. Stairs, S. P. Tendulkar, K. Vanderlinde
MMNRAS , 1–8 (2020) Preprint 12 June 2020 Compiled using MNRAS L A TEX style file v3.0
Faraday rotation measures of northern-hemisphere pulsarsusing CHIME/Pulsar
C. Ng , A. Pandhi , A. Naidu , , E. Fonseca , , V. M. Kaspi , , K. W. Masui , ,R. Mckinven , , A. Renard , P. Scholz , , I. H. Stairs , S. P. Tendulkar , , K. Vanderlinde , Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada David A. Dunlap Institute Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada Department of Physics, McGill University, 3600 rue University, Montr´eal, QC H3A 2T8, Canada McGill Space Institute, McGill University, 3550 rue University, Montr´eal, QC H3A 2A7, Canada MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA Department of Physics, Massachusetts Institute of Technology, Cambridge, 77 Massachusetts Ave, Massachusetts 02139, USA Dominion Radio Astrophysical Observatory, Herzberg Astronomy & Astrophysics Research Centre, National Research Council Canada, P.O. Box 248, Penticton, V2A 6J9, Canada Dept. of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
Accepted XXX. Received YYY; in original form ZZZ
ABSTRACT
Using commissioning data from the first year of operation of the Canadian HydrogenIntensity Mapping Experiment’s (CHIME) Pulsar backend system, we conduct a sys-tematic analysis of the Faraday Rotation Measure (RM) of the northern hemispherepulsars detected by CHIME. We present 55 new RMs as well as obtain improved RMuncertainties for 25 further pulsars. CHIME’s low observing frequency and wide band-width between 400-800 MHz contribute to the precision of our measurements, whereasthe high cadence observation provide extremely high signal-to-noise co-added data.Our results represent a significant increase of the pulsar RM census, particularly re-garding the northern hemisphere. These new RMs are for sources that are located inthe Galactic plane out to 10 kpc, as well as off the plane to a scale height of ∼
16 kpc.This improved knowledge of the Faraday sky will contribute to future Galactic large-scale magnetic structure and ionosphere modelling.
Key words: pulsars: general – techniques: polarimetric – ISM: magnetic fields
Radio pulsars have emission that is among the most polar-ized of all astronomical sources. As the linearly polarizedemission travels through the interstellar medium (ISM) inthe presence of magnetic fields, free electrons along the lineof sight (LOS) lead to Faraday rotation of the observed pul-sar radio emission. The differential of Faraday rotation (orthe change in polarization angle, ∆ PA) between two observ-ing frequencies is associated to the Rotation Measure (RM)and the observing wavelength ( λ ): ∆ PA = RM λ . (1)RM is in turn related to the number density of the freeelectrons along the LOS and the magnetic field of the LOSplasma ( B ) by: RM = .
812 rad m − ∫ d (cid:20) n e ( s ) cm − (cid:21) (cid:20) B ( s ) µ G (cid:21) · (cid:18) ds pc (cid:19) , (2)where d is the distance to the pulsar. At the same time, thepulsar emission is dispersed by the plasma electrons. Theratio of the RM to the dispersion measure (DM) provides an estimate of the integrated magnetic field strength alongthe parallel LOS: (cid:10) B (cid:107) (cid:11) = . µ G (cid:18) RMrad m − (cid:19) (cid:18) DMpc cm − (cid:19) − . (3)The Faraday rotation of pulsars is thus a powerful toolfor studying the Galactic magnetic field. The study of mag-netic field structure is important as it plays a critical rolein numerous astrophysical processes, see for example, a re-view by Noutsos (2012). Currently in the ATNF PulsarCatalogue (V1.61; Manchester et al. 2005), there are 1167pulsars with a published RM, which is approximately 42%of the full pulsar population. These pulsars are distributedthroughout the Galactic disc, mapping the (cid:10) B (cid:107) (cid:11) of over athousand LOS. Numerous previous studies have used pul-sar RMs to model the large-scale component of the Galacticmagnetic field (GMF; Noutsos et al. 2015; Han et al. 2018;Sobey et al. 2019). Pulsar RMs can also be combined with © a r X i v : . [ a s t r o - ph . I M ] J un Ng et al. extragalactic RMs for a more comprehensive view of theGalactic disc and halo (e.g. Van Eck et al. 2011).There is room for improvement in using pulsar RMs tomodel the GMF. Currently, a large fraction of the availablepulsar RMs are located near the Galactic plane and are con-centrated within a few kiloparsec from the Sun. Most of thepreviously measured RMs were obtained with the AustralianParkes telescope in the southern hemisphere which operatesat 1.4 GHz. Since Faraday rotation depends on wavelengthsquared (Eq. 1), lower frequency observations lead to moreprecise measurements of RMs. Multiple aperture array tele-scopes at low frequency have come online in recent years.They will be providing an enhanced view of the polarizedsky. These facilities include the Low-Frequency Array (LO-FAR; van Haarlem et al. 2013), the Long-Wavelength Array(LWA; Taylor et al. 2012), the Murchison Widefield Array(MWA; Tingay et al. 2013; Wayth et al. 2018). Most re-cently, the Canadian Hydrogen Intensity Mapping Exper-iment (CHIME; CHIME/FRB Collaboration et al. 2018),which is a dense-packed interferometer operating at 400-800 MHz, has also begun commissioning observations.In this paper, we present a study of pulsar RMs us-ing CHIME data. An overview of the telescope and obser-vational data is provided in Section 2 and the method ofanalysis is detailed in Section 3. We report on our results inSection 4, including 55 new RMs as well as improvement inthe uncertainties of 25 catalogue RM values. In Section 5,we discuss the implications of our work and conclude in Sec-tion 6.
CHIME is a radio telescope hosted by the Dominion RadioAstrophysical Observatory (DRAO) in British Columbia,Canada. CHIME operates across a wide bandwidth of400 −
800 MHz and has a collecting area ( ∼ ×
100 m ) andpoint-source sensitivity comparable to that of other 100-mclass radio telescopes. The reflecting surface of CHIME con-sists of four parabolic cylinders. It is a transit telescope withno moving parts. For the CHIME/Pulsar project, we com-bine the signals from the 1024 dual polarization feeds andform 10 tied-array beams that are available as raw voltages(Ng 2018). This means we can track 10 different pulsars atany given time as they transit through CHIME’s field-of-view, along the meridian. This provides very high cadencescheduling: while many of the northern hemisphere pul-sars are being monitored daily, the longest cadence to cyclethrough all sources in the northern sky is only ∼
10 days. Thisis reflected in the long co-added integration length of ourdata (Total fold ) and the high signal-to-noise (S/N) achievedas listed in Table A1. The transit time of each source is afunction of the declination; transit times can range from tensof minutes to hours for circumpolar sources. CHIME can inprinciple observe down to a declination of − ◦ . The beamformed baseband data of the CHIME/Pulsar back-end are dual-polarization, complex-sampled and split into1024 frequency channels with 8 bits per complex sample. Foreach observing scan, we generate ‘fold mode’ archives usingthe ‘Digital Signal Processing for Pulsars’ ( dspsr ) suite, anopen source GPU-based library developed by van Straten& Bailes (2011). These data are coherently dedispersed atthe known DM (taken from the ATNF catalogue) and thenfolded at the catalogue spin period with nominally 256 phasebins at 10 s sub-integration and the four Stokes ( I , Q , U , and V ) parameters are recorded. While 256 phase bins should beadequate for most of the pulsars studied in this work, wenote that using too few phase bins could potentially lead todepolarization. A number of our pulsar observations wererecorded with up to 2048 phase bins. For these sources, westep through the range of 32 to 2048 phase bins and see noobvious trend in the resulting RMs that is greater than theiruncertainties.The data have not yet been polarization calibrated.The beam shape of any aperture array is complicated, espe-cially in the case of CHIME where over a thousand ana-log input components are involved. A proper calibrationwill be implemented in the near future. Fortunately, Fara-day rotation is generally unaffected because there are nowavelength-squared dependencies in the beam shape. Wehave verified our RM analysis pipeline by cross checkingwith 100 pulsars with catalogue RMs and obtained consis-tent results for most of them (see Section 4.1). We notethat uncalibrated data could potentially show instrumen-tal polarization, where emission from Stokes I contaminatesthe other Stokes parameters. This is manifested as a peakin the Faraday spectrum centred at zero; see for example,PSRs J0026+6320, J0324+5239, B0331+45, J0426+4933 inFig C1. For a discrete sampled Faraday dispersion function,the FWHM of the theoretical RM spread function (RMSF)is given by δφ = . / ∆ ( λ ) (Brentjens & de Bruyn 2005).For CHIME, we have a δφ of about 9 rad m − . The major-ity of our RM values have a higher magnitude than this sothe presence of leakage does not cause any confusion. How-ever, this could have an effect on small RMs and is furtherdiscussed in Section 4.2. Our offline data analysis pipeline is heavily based on mod-ules from the psrchive pulsar data processing (Hotan et al.2004; van Straten et al. 2012). First, data affected by ra-dio frequency interference (RFI) are excised by identifyingoutlier intensity values both in time and frequency. Thesesub-integrations and frequency channels are set to zero us-ing paz and pazi . We create updated pulsar ephemeridesusing the tempo2 software package (Hobbs et al. 2006) andwe fit for DM using pdmp in order to properly co-add allavailable fold mode data to obtain the highest possible S/N.The S/N-optimized DM for each pulsar is listed as DM obs in Table A1. We have not taken into account any temporalDM variations in this work. DM variations up to the orderof 10 − cm − pc/yr have been reported in the literature (see,e.g. Lam et al. 2015). We have verified that offsetting the MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar folding DM by this amount does not lead to difference inRM greater than the RM uncertainty quoted here.We quantify the RM of these co-added data using the rmfit tool. An initial guess of the RM is found by bruteforce searching the RM range of ± − . At each trialRM, rmfit corrects for the associated Faraday rotation andcomputes the total linear polarization L = ( Q + U ) / acrossthe on-pulse region. rmfit then fits a Gaussian to the resul-tant RM spectrum to identify a peak RM. This RM valueis then iteratively refined as follows: the data are split intwo equal frequency bands where each data segment is in-tegrated and then compared to compute a weighted differ-ential ∆ PA. The uncertainty of ∆ PA is minimized to obtainthe best-fit RM value. Previous studies such as Morello et al.(2020) have shown that the iterative method of rmfit cansometimes under-estimate the RM uncertainty. For pulsarsthat have high enough S/N for RM to be obtained on a per-session basis (i.e., without having to co-add across multipledays), we use the spread of one standard deviation of thesedaily RM values as our uncertainty. This applies to 39 out ofthe 80 updated RMs reported in this work. For the remain-ing pulsars which are too weak to obtain per-session RM, weadopt the RM uncertainty given by the brute-force methodof rmfit on the co-added data, which is conservatively cal-culated to be the range where the Gaussian fit for the RMspectrum drops by 2- σ .Unmodelled profile evolution could lead to the additionof sine waves with amplitudes that have different frequencydependence and potentially introducing bias in the RM mea-surement. Profile evolution is expected to be most rapid atlower observing frequencies below 200 MHz (see, e.g. Phillips& Wolszczan 1992). Upon a visual inspection, we do not seesubstantial variations among the pulsars in this sample andso have not attempted to fit for 2-D pulse profiles. The ef-fect of ionospheric Faraday rotation has not been correctedin this work. To do that properly requires a careful mod-elling of the ionosphere and is out of scope for this project.However, all the observations on which this paper is basedwere obtained during the current minimum of solar activ-ity. We estimate that ionospheric RM was usually less than1 rad m − , and no more than + − even during day-time (Mevius 2018b,a). The data set used in this work is from the first year ofCHIME/Pulsar commissioning observations, which spansSeptember 2018 to 2019. In order to verify our RM pipelineand the CHIME data, we first attempt to cross check RMsfor pulsars that have a catalogue RM value. We analyse allpulsars above declination δ = ◦ detected by CHIME thathave a published RM between ±
100 rad m − . We detect un-ambiguous RMs in 100 pulsars and use them as our verifica-tion sample. As can be seen from Fig. 1, most of our observedRM (RM obs ) agree with the catalogue value (RM cat ), whichis reassuring. In addition, we measure RMs with substan-tially lower uncertainties than those in the ATNF pulsar http://psrchive.sourceforge.net/manuals/rmfit/ catalogue (V1.61) for 25 pulsars. This is likely due to thehigher precision RM made possible from our lower frequencyand large bandwidth observations, as well as the high S/Nprofiles, which result from long-duration co-added data.Eight of the RMs we measure differ significantlyfrom their catalogue values. These sources are anno-tated in Fig. 1. The catalogue RM of three of those,namely PSRs J0538+2817, J0546+2441, and J0751+1807,are close to zero, which suggests that previous studiesmight have been contaminated by spectral leakage. Wefind that the RMs of four pulsars have changed by afew to a few tens of RM units in the time betweentheir catalogue measurement epochs and our more re-cent CHIME detections. These include PSR B0144+59with RM cat = − − (Rand & Lyne 1994) com-pared to RM obs = − − , PSR B1612+07 withRM cat =40(4) rad m − (Hamilton & Lyne 1987) com-pared to RM obs =28(3) rad m − , PSR B2148+52 withRM cat = − − (Mitra et al. 2003) comparedto RM obs = − − , and PSR J2240+5832 withRM cat =24(4) rad m − (Theureau et al. 2011) compared toRM obs =17.1(11) rad m − . These differences are too big to beexplained by any ionospheric corrections. It is possible thatwe are seeing a genuine temporal evolution of these RMs overthe years, although there are no other data points in the lit-erature to help verify this. The presence of an unusual localenvironment (e.g. the Supernova Remnant of Vela (Johnstonet al. 2005), an eclipsing black widow binary (Breton et al.2013)) has been suggested to cause a change in temporalRM, although these scenarios do not seem to apply to thefour pulsars listed above. Finally, for PSR B0331+45 we ob-tain an RM obs of − − which is discrepant withthe latest result from Sobey et al. (2019) at 5.60(9) rad m − .Even though our data of PSR B0331+45 is affected by in-strumental leakage which shows up as a peak near zero in theRM spectrum (see Fig. C1), we detect a clear non-zero RMand the signal is confirmed upon inspecting the expected os-cillation in Stokes Q . Given that our work and that of Sobeyet al. (2019) are taken relatively close in time, it seems un-likely that the RM could have changed so much within ayear or so. We note that there is an older published RMof this pulsar at − − by Rand & Lyne (1994),which is consistent with our observed value. Over 500 known pulsars were detected by CHIME/Pulsarabove δ = − ◦ in the first year of commissioning. We havesufficiently high S/N data for RM measurement for 109 ofthese pulsars that do not already have published RM values.We obtain new RMs for 55 of these pulsars; see Table A1for details, and Figs. C1-C3 for the individual RM spectra.We are not able to quantify RMs for the remaining pulsarsbecause of two reasons: (1) instrumental leakage dominates30 of those, which could potentially be improved when apolarization calibration scheme is carried out on CHIMEdata in the future; (2) no RM peak is detected in 24 pulsars,which could be because these pulsars are intrinsically weaklypolarized. Refer to Appendix C for a list of these pulsars.Thirteen of these 55 pulsars were already studied usingLOFAR in Sobey et al. (2019), although they did not detectany significant RM at the time (refer to Table 2 in that pub- MNRAS , 1–8 (2020)
Ng et al.
100 75 50 25 0 25 50 75 100 RM cat [rad m ] R M o b s [ r a d m ] J0538+2817J0751+1807B2148+52 J0546+2441B0331+45B1612+07J2240+5832B0144+59
Observed PSRs Compared to PSR Catalogue RM cat = RM obs Error
Figure 1.
A comparison between RM obs and RM cat for 100pulsars above δ = ◦ detected by CHIME. The black linecorresponds to the RM obs = RM cat trend which we expectto see. PSRs B0144+59, B0331+45, J0538+2817, J0546+2441,J0751+1807, B1612+07, B2148+52 and J2240+5832 are high-lighted as they significantly deviate from the RM obs = RM cat trend; these eight pulsars are discussed further in the main text. lication). This may be because LOFAR’s frequency channelwidths are sufficiently broad that they lose >
50% sensitivityfor | RM | >
163 rad m − , whereas for CHIME/Pulsar, with ourfrequency resolution of 390 kHz, we maintain full sensitivityout to a RM of roughly 1000 rad m − . Some of these pulsarslie along the Galactic plane, and LOFAR could be sufferingfrom more scattering and depolarization at the high DM andRM due to its low observing frequency. We note that thereis likely some degree of profile scattering for some of the pul-sars in the CHIME band as well. We have not attempted tomodel the effect of scattering on RM here; the difference isexpected to be small and within the uncertainty of our RMvalues. Finally, the remarkably long duration from the co-addition of data significantly increases our ability to conductthis kind of analysis on a large number of pulsars that wouldotherwise not have the required S/N to robustly measure theRM.As mentioned before, the data configuration ofCHIME implies that we have a theoretical RMSF of ∼ − . Three of our new RMs fall within this range,notably PSR J1647+6608 with RM obs =7(3) rad m − ,PSR J1911+1347 with RM obs = − − , andPSR J2340+08 with RM obs = − − . Judgingfrom their respective RM spectrum (see Fig. C1-C3), theRM peak is clearly distinct from zero. This made us believethat these new RMs are reliable and not due to confusionwith instrumental leakage. We have updated 25 existing RM values of northern hemi-sphere pulsars and measured 55 new RMs. These 80 pulsarsare located in our full range of Right Ascension (RA) and δ , spanning 1.5 ◦ ≤ RA ≤ . ◦ and − . ◦ ≤ δ ≤ . ◦ . Interms of Galactic coordinates, which provide useful insightfor studies looking at the Milky Way’s magnetic field along longitudinal LOS, the pulsars lie within Galactic longitudeof . ◦ ≤ l ≤ . ◦ and Galactic latitude of − . ◦ ≤ b ≤ . ◦ . The range of updated RMs reported in this work liesbetween −
295 rad m − ≤ RM obs ≤
338 rad m − . The average | RM obs | in this study is roughly 70 rad m − . Combining theDM obs listed in Table A1, we can apply Equation 3 to cal-culate the LOS parallel magnetic field strength, (cid:10) B (cid:107) (cid:11) (lastcolumn of Table A1). According to Sun & Reich (2010), thestrength of the regular halo magnetic field is about 2 µ G,with which our results are largely consistent.If we take into account the DM-derived distance of thesepulsars as listed in the ATNF Pulsar Catalogue (based onthe electron density model of Yao et al. 2017), we can locatethe derived (cid:10) B (cid:107) (cid:11) on a 3-D plot in Cartesian coordinates, asshown in Figs. C4-C6. Note that most of the known pul-sars do not have independent distance measurements (e.g.from parallax), and a majority of the pulsar distances areobtained from their DM, combined with a model of the freeelectron distribution, which is said to have uncertainty up tosome 20%. Keeping the caveat of the distance uncertainty inmind, we can still form an overview picture of the updatedFaraday sky. In Fig. C4, we overlay the location of RM val-ues from this work as well as all existing catalogue pulsarRMs with a simulation of the spiral arm structure of ourMilky Way. It can be seen that most of our RMs fall withinquadrants III and IV, and they also somewhat follow the armstructure. Compared to the recent LOFAR study by Sobeyet al. (2019), we typically measure RMs farther out along theGalactic plane (up to ∼
10 kpc) whereas LOFAR’s sample ismostly concentrated near the Sun. This is likely due to lesssevere scattering and depolarization at the higher observingfrequency of CHIME. In terms of scale height ( z ), we covera large range, detecting RMs up to z ∼
16 kpc. From our 80updated RMs, we see a similar dichotomy already mentionedby Sobey et al. (2019), that (cid:10) B (cid:107) (cid:11) values above the Galacticplane tend to be positive while those below the plane tendto be negative. We present new measurements of RMs for northern radiopulsars, using commissioning data from CHIME/Pulsar. Wereport 55 new RMs , and provide improved values and un-certainties for 25 pulsars with previously catalogued RMs.The wide bandwidth of CHIME has enabled our high RMprecision. The observing frequency of 400-800 MHz is at asweet spot for RM studies, low enough to take advantageof the wavelength squared dependency of RM and the steepspectrum of most pulsars, but not so low as to be hinderedby scattering and depolarization at high DM and RM. Thehigh cadence observations of CHIME also provide excellentS/N in our co-added data. We note that ionospheric RM cor-rections have not been applied in this work and it remainsthe biggest source of systematic uncertainty in our RMs.The 80 updated RMs reported here cover a large regionof the Milky Way, both deep in the Galactic plane and farout in the halo. The derived (cid:10) B (cid:107) (cid:11) values are comparable tothe average magnetic field strength of our Galaxy. Overall,this work improves our knowledge of the Faraday sky, withpotential implications on future Galactic large-scale struc-ture and ionospheric modelling studies. MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar ACKNOWLEDGEMENTS
We are grateful to the staff of the Dominion Radio Astro-physical Observatory, which is operated by the National Re-search Council Canada. Pulsar research at UBC is supportedby an NSERC Discovery Grant and by the Canadian Insti-tute for Advanced Research. CN is a SOSCIP TalentEdgefellow. AP was supported by the Summer UndergraduateResearch Program (SURP) in astronomy & astrophysics atthe University of Toronto. V.M.K. holds the Lorne Trot-tier Chair in Astrophysics & Cosmology and a Canada Re-search Chair and receives support from an NSERC Discov-ery Grant and Herzberg Award, from an R. Howard WebsterFoundation Fellowship from the Canadian Institute for Ad-vanced Research (CIFAR), and from the FRQNT Centrede Recherche en Astrophysique du Quebec. P.S. is a Dun-lap Fellow and an NSERC Postdoctoral Fellow. The Dun-lap Institute is funded through an endowment establishedby the David Dunlap family and the University of Toronto.We thank Tom Landecker for useful discussion and BradleyMeyers for carefully reading the manuscript. We also thankJumei Yao for providing the electron density data for theYMW2016 model.
REFERENCES
Brentjens M. A., de Bruyn A. G., 2005, A&A, 441, 1217Breton R. P., et al., 2013, ApJ, 769, 108Brinkman C., Freire P. C. C., Rankin J., Stovall K., 2018, MN-RAS, 474, 2012CHIME/FRB Collaboration et al., 2018, ApJ, 863, 48Gentile P. A., et al., 2018, ApJ, 862, 47Hamilton P. A., Lyne A. G., 1987, MNRAS, 224, 1073Han J. L., Manchester R. N., van Straten W., Demorest P., 2018,ApJS, 234, 11Hankins T. H., Rankin J. M., 2010, AJ, 139, 168Hobbs G. B., Edwards R. T., Manchester R. N., 2006, MNRAS,369, 655Hotan A. W., van Straten W., Manchester R. N., 2004, Publ.Astron. Soc. Australia, 21, 302Johnston S., Hobbs G., Vigeland S., Kramer M., Weisberg J. M.,Lyne A. G., 2005, MNRAS, 364, 1397Lam M. T., Cordes J. M., Chatterjee S., Dolch T., 2015, ApJ,801, 130Lynch R. S., et al., 2013, ApJ, 763, 81Manchester R. N., Hobbs G. B., Teoh A., Hobbs M., 2005, VizieROnline Data Catalog, 7245, 0Mevius M., 2018a, RMextract: Ionospheric Faraday Rotation cal-culator (ascl:1806.024)Mevius M., 2018b, in Astrophysics and Space Science Library.p. 103, doi:10.1007/978-3-319-23434-2 7Mitra D., Wielebinski R., Kramer M., Jessner A., 2003, A&A,398, 993Morello V., et al., 2020, MNRAS, 493, 1165Ng C., 2018, in Weltevrede P., Perera B. B. P., Pre-ston L. L., Sanidas S., eds, IAU Symposium Vol. 337,Pulsar Astrophysics the Next Fifty Years. pp 179–182( arXiv:1711.02104 ), doi:10.1017/S1743921317010638Noutsos A., 2012, Space Sci. Rev., 166, 307Noutsos A., et al., 2015, A&A, 576, A62Phillips J. A., Wolszczan A., 1992, ApJ, 385, 273Rand R. J., Lyne A. G., 1994, MNRAS, 268, 497Sobey C., et al., 2019, MNRAS, 484, 3646Sun X.-H., Reich W., 2010, Research in Astronomy and Astro-physics, 10, 1287 Taylor G. B., et al., 2012, Journal of Astronomical Instrumenta-tion, 1, 1250004Theureau G., et al., 2011, A&A, 525, A94Tingay S. J., et al., 2013, Publ. Astron. Soc. Australia, 30, e007Van Eck C. L., et al., 2011, ApJ, 728, 97Wayth R. B., et al., 2018, Publ. Astron. Soc. Australia, 35, 33Yao J. M., Manchester R. N., Wang N., 2017, ApJ, 835, 29van Haarlem M. P., et al., 2013, A&A, 556, A2van Straten W., Bailes M., 2011, Publications of the AstronomicalSociety of Australia, 28, 1van Straten W., Demorest P., Oslowski S., 2012, AstronomicalResearch and Technology, 9, 237
APPENDIX A: SUMMARY OF RESULTS
Summarized in Table A1 are the principal results of thisstudy using the rmfit tool on co-added pulsar observationsfrom CHIME/Pulsar. This Table comprises 80 pulsars: 55new RM results that have not been previously publishedand 25 updated RMs to the pulsar catalogue (version 1.61)with tighter bounds on the uncertainty.Column 1 shows the pulsar name in B1950 or J2000coordinate systems; the pulsars are listed in order of as-cending RA. Columns 2 − − −
11. The uncertainty of our observed RMcomes from the spread of the per-session RMs. When thatis not available for the low S/N pulsars, uncertainty is takenfrom the RM spectrum Gaussian fit width calculated by rm-fit . Our RMs do not include any ionospheric corrections.Columns 12 −
13 list the (cid:10) B (cid:107) (cid:11) and associated error derivedfrom applying Equation 3 to our DM and RM results. MNRAS000
13 list the (cid:10) B (cid:107) (cid:11) and associated error derivedfrom applying Equation 3 to our DM and RM results. MNRAS000 , 1–8 (2020)
Ng et al. T a b l e A : Su mm a r y o f c o - a dd e d R M s o b t a i n e d i n t h i s w o r k . S ee A pp e nd i x A f o r a d e t a il e dd e s c r i p t i o n o f e a c h c o l u m n . P S RR M ca t ± R e f M J D T o t a l f o l d S / N D M ob s ± R M ob s ± (cid:10) B (cid:107) (cid:11) ± ( r a d m − )( r a d m − )( h r s )( p cc m − )( p cc m − )( r a d m − )( r a d m − )( µ G )( µ G ) J + - . . . − − . . J + - . . . − − . . J + - . . . − − . . B + − . . h l - . . . − . . − . . B + − . . r l - . . . − . . − . . B + − . . h l - . . . − − . . J + - . . . − − . . J + - . . . − − . . B + . . s b g + - . . . − . . − . . B + − . . m w k j - . . . − . . − . . J + - . . . . . . . B + . . h l - . . . . . . . J + - . . . − − . . J + - . . . − − . . J + − . . b f r s - . . . − . . − . . J + − . . m w k j - . . . . . J + - . . . . . . . J + . . h m v d - . . . . . J + - . . . . . J + - . . . . . J + - . . . − − . . J + - . . . . . J + - . . . − − . . J + - . . . . . . . J + - . . . − − . . J + . . h m v d - . . . . . J + . . h m v d - . . . . . J + - . . . . . J + - . . . − . . − . . J + − . . h m v d - . . . − . . − . . J + - . . . . . . . J + - . . . . . . . B + . . h l - . . . . . B + A ***58359 - . . . . . J + - . . . . . J + - . . . . . J + - . . . . . J + m d + - . . . . . B + . . h m v d - . . . . . J + - . . . . . C o n t i nu e d o nn e x t p ag e MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar T a b l e A c o n t i nu e d f r o m p r e v i o u s p a g e P S RR M ca t ± R e f M J D T o t a l f o l d S / N D M ob s ± R M ob s ± (cid:10) B (cid:107) (cid:11) ± ( r a d m − )( r a d m − )( h r s )( p cc m − )( p cc m − )( r a d m − )( r a d m − )( µ G )( µ G ) J + - . . . . . . . J + - . . . . . J + - . . . − − . . J - - . . . − − . . B + - . . . . . J + - . . . . . J + − . . h m v d - . . . − . . − . . B + − . . h l - . . . − − . . B + . . h l - . . . . . . . J + - . . . − − . . J + - . . . . . . . J + - . . . − − . . J + - . . . − − . . J + - . . . . . J + − m d + - . . . − . . − . . B + - . . . − − . . J + - . . . . . J + - . . . − − . . J + − . . h m v d - . . . − . . − . . J + - . . . − − . . B + − . . h l - . . . − . . − . . J + - . . . − − . . B + − . . h r - . . . − − . . J + - . . . − − . . J + - . . . . . B + − . . m w k j - . . . − . . − . . J + - . . . − − . . J + - . . . − − . . J + - . . . − . . − . . J + - . . . − − . . J + - . . . − . . − . . J + - . . . − − . . J + − . . h m v d - . . . − . . − . . J + . . t p c + - . . . . . . . J + - . . . − . . − . . J + - . . . . . . . J + - . . . − − . . J + - . . . − . . − . . J + - . . . − − . . J + - . . . − . . − . . MNRAS000
Ng et al. T a b l e A : Su mm a r y o f c o - a dd e d R M s o b t a i n e d i n t h i s w o r k . S ee A pp e nd i x A f o r a d e t a il e dd e s c r i p t i o n o f e a c h c o l u m n . P S RR M ca t ± R e f M J D T o t a l f o l d S / N D M ob s ± R M ob s ± (cid:10) B (cid:107) (cid:11) ± ( r a d m − )( r a d m − )( h r s )( p cc m − )( p cc m − )( r a d m − )( r a d m − )( µ G )( µ G ) J + - . . . − − . . J + - . . . − − . . J + - . . . − − . . B + − . . h l - . . . − . . − . . B + − . . r l - . . . − . . − . . B + − . . h l - . . . − − . . J + - . . . − − . . J + - . . . − − . . B + . . s b g + - . . . − . . − . . B + − . . m w k j - . . . − . . − . . J + - . . . . . . . B + . . h l - . . . . . . . J + - . . . − − . . J + - . . . − − . . J + − . . b f r s - . . . − . . − . . J + − . . m w k j - . . . . . J + - . . . . . . . J + . . h m v d - . . . . . J + - . . . . . J + - . . . . . J + - . . . − − . . J + - . . . . . J + - . . . − − . . J + - . . . . . . . J + - . . . − − . . J + . . h m v d - . . . . . J + . . h m v d - . . . . . J + - . . . . . J + - . . . − . . − . . J + − . . h m v d - . . . − . . − . . J + - . . . . . . . J + - . . . . . . . B + . . h l - . . . . . B + A ***58359 - . . . . . J + - . . . . . J + - . . . . . J + - . . . . . J + m d + - . . . . . B + . . h m v d - . . . . . J + - . . . . . C o n t i nu e d o nn e x t p ag e MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar T a b l e A c o n t i nu e d f r o m p r e v i o u s p a g e P S RR M ca t ± R e f M J D T o t a l f o l d S / N D M ob s ± R M ob s ± (cid:10) B (cid:107) (cid:11) ± ( r a d m − )( r a d m − )( h r s )( p cc m − )( p cc m − )( r a d m − )( r a d m − )( µ G )( µ G ) J + - . . . . . . . J + - . . . . . J + - . . . − − . . J - - . . . − − . . B + - . . . . . J + - . . . . . J + − . . h m v d - . . . − . . − . . B + − . . h l - . . . − − . . B + . . h l - . . . . . . . J + - . . . − − . . J + - . . . . . . . J + - . . . − − . . J + - . . . − − . . J + - . . . . . J + − m d + - . . . − . . − . . B + - . . . − − . . J + - . . . . . J + - . . . − − . . J + − . . h m v d - . . . − . . − . . J + - . . . − − . . B + − . . h l - . . . − . . − . . J + - . . . − − . . B + − . . h r - . . . − − . . J + - . . . − − . . J + - . . . . . B + − . . m w k j - . . . − . . − . . J + - . . . − − . . J + - . . . − − . . J + - . . . − . . − . . J + - . . . − − . . J + - . . . − . . − . . J + - . . . − − . . J + − . . h m v d - . . . − . . − . . J + . . t p c + - . . . . . . . J + - . . . − . . − . . J + - . . . . . . . J + - . . . − − . . J + - . . . − . . − . . J + - . . . − − . . J + - . . . − . . − . . MNRAS000 , 1–8 (2020)
Ng et al.
Table A2.
Summary of the references for the catalogue RMslisted in Table A1.Shorthand Reference (lowest) Centre frequency (MHz) Ionospheric RM correctedbfrs18 Brinkman et al. (2018) 327 Ngmd+18 Gentile et al. (2018) 1400 Nhl87 Hamilton & Lyne (1987) 408 Yhmvd18 Han et al. (2018) 774 Yhr10 Hankins & Rankin (2010) 50 Nlbr+13 Lynch et al. (2013) 350/820 Nmwkj03 Mitra et al. (2003) 1400 Nrl94 Rand & Lyne (1994) 1400 Nsbg+19 Sobey et al. (2019) 110 Ytpc+11 Theureau et al. (2011) 1100 N
APPENDIX B: SUMMARY OF FARADAYSPECTRA OBSERVATIONS
Figures C1 through C3 show the individual Faraday spec-tra of the 80 RM results presented in Table A1. The x-axes show the appropriate RM range that incorporates thepeak RM values. The y-axes show normalized polarized fluxin arbitrary units as our data are uncalibrated in polariza-tion. Peaks centred at 0 rad m − and symmetric peaks about0 rad m − are due to instrumental leakage discussed in Sec-tion 2. The RM obs is shown as a vertical dashed line and itscorresponding uncertainty is represented by vertical solidlines, although in almost all cases the uncertainty range istoo small to visually separate the three lines. When avail-able, the catalogue RM (RM cat ) is represented by a verticalred dash-dot line and its corresponding uncertainty regionis marked by the shaded hatch. APPENDIX C: PULSARS WITH NODETECTED RM
In addition to the 80 RMs reported in this work, afurther 54 pulsars were studied although no RM wasdetected in them. Instrumental leakage dominated30 pulsars, namely PSRs J0023+0923, J0051+0423,J0243+6027, J0329+1654, J0458 − − − − −
13, J1744 − − − − − − − − − − − This paper has been typeset from a TEX/L A TEX file prepared bythe author. MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J0006+1834
300 200 100 0 100 200 3000.00.20.40.60.81.0
J0026+6320
300 200 100 0 100 200 3000.00.20.40.60.81.0
J0058+6125
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B0138+59
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x B0144+59
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B0154+61
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0201+7005
300 200 100 0 100 200 3000.00.20.40.60.81.0
J0324+5239
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x B0331+45
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B0339+53
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0340+4130
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B0355+54
300 200 100 0 100 200 3000.00.20.40.60.81.0 P o l a r i z e d F l u x J0426+4933
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0453+1559
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0517+2212
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0538+2817
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J0540+3207
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0546+2441
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0555+3948
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0613+3731
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J0614+83
300 200 100 0 100 200 3000.00.20.40.60.81.0
J0627+0649
300 200 100 0 100 200 3000.00.20.40.60.81.0
J0646+0905
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J0711+0931
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] P o l a r i z e d F l u x J0740+6620
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J0751+1807
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J0815+0939
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J0843+0719
Figure C1.
Faraday spectra of the 80 pulsars in this work. Refer to text for further description of the figures.MNRAS000
Faraday spectra of the 80 pulsars in this work. Refer to text for further description of the figures.MNRAS000 , 1–8 (2020) Ng et al.
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J1434+7257
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1518+4904
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1538+2345
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1544+4937
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x B1612+07
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B1639+36A
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1647+6608
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1710+4923
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J1736+05
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1738+0333
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B1802+03
300 200 100 0 100 200 3000.00.20.40.60.81.0
J1821+0155
100 50 0 50 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J1834+10
300 200 100 0 100 200 3000.00.20.40.60.81.0
J1900+30
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1911+1347
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1918-0642
300 200 100 0 100 200 3000.00.20.40.60.81.0 P o l a r i z e d F l u x B1926+18
100 75 50 25 0 25 50 75 1000.20.00.20.40.60.81.0
J1946+2535
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J1946+2611
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B1952+29
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x B2002+31
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2010+2845
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2011+3331
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2013+3058
300 200 100 0 100 200 300
Rotation Measure [rad m ] P o l a r i z e d F l u x J2016+1948
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J2017+5906
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J2019+2425
300 200 100 0 100 200 300
Rotation Measure [rad m ] B2025+21
Figure C2.
Continued from the previous page. MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar
300 200 100 0 100 200 3000.00.20.40.60.81.0 P o l a r i z e d F l u x J2027+4557
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2040+1657
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2045+0912
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2047+5029
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x B2053+36
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2102+38
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B2122+13
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2138+4911
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J2139+00
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
B2148+52
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2208+4056
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2208+5500
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J2216+5759
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2217+5733
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2227+30
300 200 100 0 100 200 3000.00.20.40.60.81.0
J2229+6114
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0 P o l a r i z e d F l u x J2234+2114
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2240+5832
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2243+1518
100 75 50 25 0 25 50 75 1000.00.20.40.60.81.0
J2302+4442
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] P o l a r i z e d F l u x J2310+6706
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J2319+6411
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J2340+08
100 75 50 25 0 25 50 75 100
Rotation Measure [rad m ] J2343+6221
Figure C3.
Continued from the previous page.MNRAS000
Continued from the previous page.MNRAS000 , 1–8 (2020) Ng et al.
20 15 10 5 0 5 10 15 20
X [kpc] Y [ k p c ] Catalogue ResultsObserved Results B [ G ] Figure C4.
X-Y plane of the Milky Way, where the Sun is defined to be at (X,Y)=(0,8.3) kpc and the Galactic Centre at (X,Y)=(0,0) kpc.The pulsars with catalogue RM values are shown as circles, whereas the 80 updated RMs from this work are represented by squares. Thecolour scale of these symbols gives the (cid:10) B (cid:107) (cid:11) . Pulsars with z > | | kpc are not shown for clarity of the local distribution. The electrondensity in the plane of the Galaxy used in the YMW16 model is also shown in gray scale.
20 15 10 5 0 5 10 15 20
X [kpc] Z [ k p c ] Catalogue ResultsObserved Results B [ G ] Figure C5.
X-Z plane of the Milky Way, with the same plotting organization as Fig. C4.MNRAS , 1–8 (2020) otation measures of pulsars using CHIME/Pulsar
15 10 5 0 5 10 15
Y [kpc] Z [ k p c ] Catalogue ResultsObserved Results B [ G ] Figure C6.
Y-Z plane of the Milky Way, with the same plotting organization as Fig. C4.MNRAS000