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1. Discovery and timing of ten new millisecond pulsars in the globular cluster Terzan 5

Author: Padmanabh, P. V., Ransom, S. M., Freire, P. C. C., Ridolfi, A., Taylor, J. D., Choza, C., Clark, C. J., Abbate, F., Bailes, M., Barr, E. D., Buchner, S., Burgay, M., DeCesar, M. E., Chen, W., Corongiu, A., Champion, D. J., Dutta, A., Geyer, M., Hessels, J. W. T., Kramer, M., Possenti, A., Stairs, I. H., Stappers, B. W., Krishnan, V. Venkatraman, Vleeschower, L., and Zhang, L.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report the discovery of ten new pulsars in the globular cluster Terzan 5 as part of the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed Terzan 5 at L-band (856--1712 MHz) with the MeerKAT radio telescope for four hours on two epochs, and performed acceleration searches of 45 out of 288 tied-array beams covering the core of the cluster. We obtained phase-connected timing solutions for nine discoveries, covering nearly two decades of archival observations from the Green Bank Telescope for all but one. Highlights include PSR J1748$-$2446ao which is an eccentric ($e = 0.32$) wide-orbit (orbital period $P_{\rm b} = 57.55$ d) system. We were able to measure the rate of advance of periastron ($\dot{\omega}$) for this system allowing us to determine a total mass of $3.17 \pm \, 0.02\, \rm M_{\odot}$. With a minimum companion mass ($M_{\rm c}$) of $\sim 0.8\, \rm M_{\odot}$, PSR J1748$-$2446ao is a candidate double neutron star (DNS) system. If confirmed to be a DNS, it would be the fastest spinning pulsar ($P = 2.27$ ms) and the longest orbital period measured for any known DNS system. PSR J1748$-$2446ap has the second highest eccentricity for any recycled pulsar ($e \sim 0.905$) and for this system we can measure the total mass ($1.997 \pm 0.006\, \rm M_{\odot}$) and also estimate the individual pulsar and companion masses. PSR J1748$-$2446ar is an eclipsing redback (minimum $M_{\rm c} \sim 0.34\, \rm M_{\odot}$) system whose properties confirm it to be the counterpart to a previously published source identified in radio and X-ray imaging. With these discoveries, the total number of confirmed pulsars in Terzan 5 is 49, the highest for any globular cluster so far. These discoveries further enhance the rich set of pulsars known in Terzan 5 and provide scope for a deeper understanding of binary stellar evolution, cluster dynamics and ensemble population studies., Comment: 23 pages, 11 figures, 5 tables, published in A&A
Published: 2024
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2. The Green Bank North Celestial Cap Survey IX: Timing Follow-up for 128 Pulsars

Author: McEwen, A. E., Swiggum, J. K., Kaplan, D. L., Tan, C. M., Meyers, B. W., Fonseca, E., Agazie, G. Y., Chawla, P., Crowter, K., DeCesar, M. E., Dolch, T., Dong, F. A., Fiore, W., Good, D. C., Istrate, A. G., Kaspi, V. M., Kondratiev, V. I., van Leeuwen, J., Levin, L., Lewis, E. F., Lynch, R. S., Masui, K. W., McKee, J. W., McLaughlin, M. A., Noori, H. Al, Parent, E., Ransom, S. M., Siemens, X., Spiewak, R., and Stairs, I. H.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The Green Bank North Celestial Cap survey is one of the largest and most sensitive searches for pulsars and transient radio objects. Observations for the survey have finished; priorities have shifted toward long-term monitoring of its discoveries. In this study, we have developed a pipeline to handle large datasets of archival observations and connect them to recent, high-cadence observations taken using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. This pipeline handles data for 128 pulsars and has produced measurements of spin, positional, and orbital parameters that connect data over observation gaps as large as 2000 days. We have also measured glitches in the timing residuals for five of the pulsars included and proper motion for 19 sources (13 new). We include updates to orbital parameters for 19 pulsars, including 9 previously unpublished binaries. For two of these binaries, we provide updated measurements of post-Keplerian binary parameters, which result in much more precise estimates of the total masses of both systems. For PSR J0509+3801, the much improved measurement of the Einstein delay yields much improved mass measurements for the pulsar and its companion, 1.399(6)\Msun and 1.412(6)\Msun, respectively. For this system, we have also obtained a measurement of the orbital decay due to the emission of gravitational waves: $\dot{P}_{\rm B} = -1.37(7)\times10^{-12}$, which is in agreement with the rate predicted by general relativity for these masses., Comment: accepted for publication in The Astrophysical Journal
Published: 2023
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3. The black widow pulsar J1641+8049 in the optical, radio and X-rays

Author: Kirichenko, A. Yu., Zharikov, S. V., Karpova, A. V., Fonseca, E., Zyuzin, D. A., Shibanov, Yu. A., López, E. A., Gilfanov, M. R., Cabrera-Lavers, A., Geier, S., Dong, F. A., Good, D. C., McKee, J. W., Meyers, B. W., Stairs, I. H., McLaughlin, M. A., and Swiggum, J. K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: PSR J1641+8049 is a 2 ms black widow pulsar with the 2.2 h orbital period detected in the radio and $\gamma$-rays. We performed new phase-resolved multi-band photometry of PSR J1641+8049 using the OSIRIS instrument at the Gran Telescopio Canarias. The obtained data were analysed together with the new radio-timing observations from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), the X-ray data from the Spectrum-RG/eROSITA all-sky survey, and all available optical photometric observations. An updated timing solution based on CHIME data is presented, which accounts for secular and periodic modulations in pulse dispersion. The system parameters obtained through the light curve analysis, including the distance to the source 4.6-4.8 kpc and the orbital inclination 56-59 deg, are found to be consistent with previous studies. However, the optical flux of the source at the maximum brightness phase faded by a factor of $\sim$2 as compared to previous observations. Nevertheless, the face of the J1641+8049 companion remains one of the most heated (8000-9500 K) by a pulsar among the known black widow pulsars. We also report a new estimation on the pulsar proper motion of $\approx$2 mas yr$^{-1}$, which yields a spin down luminosity of $\approx$4.87$\times 10^{34}$ ergs s$^{-1}$ and a corresponding heating efficiency of the companion by the pulsar of 0.3-0.7. The pulsar was not detected in X-rays implying its X-ray-luminosity was <3 $\times$ 10$^{31}$ erg s$^{-1}$ at the date of observations., Comment: Accepted for publication in MNRAS
Published: 2023
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4. A MeerKAT view of the double pulsar eclipses -- Geodetic precession of pulsar B and system geometry

Author: Lower, M. E., Kramer, M., Shannon, R. M., Breton, R. P., Wex, N., Johnston, S., Bailes, M., Buchner, S., Hu, H., Krishnan, V. Venkatraman, Blackmon, V. A., Camilo, F., Champion, D. J., Freire, P. C. C., Geyer, M., Karastergiou, A., van Leeuwen, J., McLaughlin, M. A., Reardon, D. J., and Stairs, I. H.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics, General Relativity and Quantum Cosmology
Abstract: The double pulsar system, PSR J0737$-$3039A/B, consists of two neutron stars bound together in a highly relativistic orbit that is viewed nearly edge-on from the Earth. This alignment results in brief radio eclipses of the fast-rotating pulsar A when it passes behind the toroidal magnetosphere of the slow-rotating pulsar B. The morphology of these eclipses is strongly dependent on the geometric orientation and rotation phase of pulsar B, and their time-evolution can be used to constrain the geodetic precession rate of the pulsar. We demonstrate a Bayesian inference framework for modelling eclipse light-curves obtained with MeerKAT between 2019-2023. Using a hierarchical inference approach, we obtained a precession rate of $\Omega_{\rm SO}^{\rm B} = {5.16^{\circ}}^{+0.32^{\circ}}_{-0.34^{\circ}}$ yr$^{-1}$ for pulsar B, consistent with predictions from General Relativity to a relative uncertainty of 6.5%. This updated measurement provides a 6.1% test of relativistic spin-orbit coupling in the strong-field regime. We show that a simultaneous fit to all of our observed eclipses can in principle return a $\sim$1.5% test of spin-orbit coupling. However, systematic effects introduced by the current geometric orientation of pulsar B along with inconsistencies between the observed and predicted eclipse light curves result in difficult to quantify uncertainties. Assuming the validity of General Relativity, we definitively show that the spin-axis of pulsar B is misaligned from the total angular momentum vector by $40.6^{\circ} \pm 0.1^{\circ}$ and that the orbit of the system is inclined by approximately $90.5^{\circ}$ from the direction of our line of sight. Our measured geometry for pulsar B suggests the largely empty emission cone contains an elongated horseshoe shaped beam centered on the magnetic axis, and that it may not be re-detected as a radio pulsar until early-2035., Comment: Abridged abstract. 13 pages, 9 figures and 2 tables
Published: 2023
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5. Comparing recent PTA results on the nanohertz stochastic gravitational wave background

Author: The International Pulsar Timing Array Collaboration, Agazie, G., Antoniadis, J., Anumarlapudi, A., Archibald, A. M., Arumugam, P., Arumugam, S., Arzoumanian, Z., Askew, J., Babak, S., Bagchi, M., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Bathula, A., Bécsy, B., Berthereau, A., Bhat, N. D. R., Blecha, L., Bonetti, M., Bortolas, E., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Burnette, R., Caballero, R. N., Cameron, A., Case, R., Chalumeau, A., Champion, D. J., Chanlaridis, S., Charisi, M., Chatterjee, S., Chatziioannou, K., Cheeseboro, B. D., Chen, S., Chen, Z. -C., Cognard, I., Cohen, T., Coles, W. A., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Curyło, M., Cutler, C. J., Dai, S., Dandapat, S., Deb, D., DeCesar, M. E., DeGan, D., Demorest, P. B., Deng, H., Desai, S., Desvignes, G., Dey, L., Dhanda-Batra, N., Di Marco, V., Dolch, T., Drachler, B., Dwivedi, C., Ellis, J. A., Falxa, M., Feng, Y., Ferdman, R. D., Ferrara, E. C., Fiore, W., Fonseca, E., Franchini, A., Freedman, G. E., Gair, J. R., Garver-Daniels, N., Gentile, P. A., Gersbach, K. A., Glaser, J., Good, D. C., Goncharov, B., Gopakumar, A., Graikou, E., Grießmeier, J. -M., Guillemot, L., Gültekin, K., Guo, Y. J., Gupta, Y., Grunthal, K., Hazboun, J. S., Hisano, S., Hobbs, G. B., Hourihane, S., Hu, H., Iraci, F., Islo, K., Izquierdo-Villalba, D., Jang, J., Jawor, J., Janssen, G. H., Jennings, R. J., Jessner, A., Johnson, A. D., Jones, M. L., Joshi, B. C., Kaiser, A. R., Kaplan, D. L., Kapur, A., Kareem, F., Karuppusamy, R., Keane, E. F., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kharbanda, D., Kikunaga, T., Klein, T. C., Kolhe, N., Kramer, M., Krishnakumar, M. A., Kulkarni, A., Laal, N., Lackeos, K., Lam, M. T., Lamb, W. G., Larsen, B. B., Lazio, T. J. W., Lee, K. J., Levin, Y., Lewandowska, N., Littenberg, T. B., Liu, K., Liu, T., Liu, Y., Lommen, A., Lorimer, D. R., Lower, M. E., Luo, J., Luo, R., Lynch, R. S., Lyne, A. G., Ma, C. -P., Maan, Y., Madison, D. R., Main, R. A., Manchester, R. N., Mandow, R., Mattson, M. A., McEwen, A., McKee, J. W., McLaughlin, M. A., McMann, N., Meyers, B. W., Meyers, P. M., Mickaliger, M. B., Miles, M., Mingarelli, C. M. F., Mitridate, A., Natarajan, P., Nathan, R. S., Ng, C., Nice, D. J., Niţu, I. C., Nobleson, K., Ocker, S. K., Olum, K. D., Osłowski, S., Paladi, A. K., Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Petrov, P., Pol, N. S., Porayko, N. K., Possenti, A., Prabu, T., Leclere, H. Quelquejay, Radovan, H. A., Rana, P., Ransom, S. M., Ray, P. S., Reardon, D. J., Rogers, A. F., Romano, J. D., Russell, C. J., Samajdar, A., Sanidas, S. A., Sardesai, S. C., Schmiedekamp, A., Schmiedekamp, C., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Singha, J., Siwek, M. S., Speri, L., Spiewak, R., Srivastava, A., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Stovall, K., Sun, J. P., Surnis, M., Susarla, S. C., Susobhanan, A., Swiggum, J. K., Takahashi, K., Tarafdar, P., Taylor, J., Taylor, S. R., Theureau, G., Thrane, E., Thyagarajan, N., Tiburzi, C., Toomey, L., Turner, J. E., Unal, C., Vallisneri, M., van der Wateren, E., van Haasteren, R., Vecchio, A., Krishnan, V. Venkatraman, Verbiest, J. P. W., Vigeland, S. J., Wahl, H. M., Wang, S., Wang, Q., Witt, C. A., Wang, J., Wang, L., Wayt, K. E., Wu, Z., Young, O., Zhang, L., Zhang, S., Zhu, X. -J., and Zic, A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: The Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational wave background (GWB). Given that each PTA made different choices in modeling their data, we perform a comparison of the GWB and individual pulsar noise parameters across the results reported from the PTAs that constitute the International Pulsar Timing Array (IPTA). We show that despite making different modeling choices, there is no significant difference in the GWB parameters that are measured by the different PTAs, agreeing within $1\sigma$. The pulsar noise parameters are also consistent between different PTAs for the majority of the pulsars included in these analyses. We bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and PTAs, finding that under this model there is a reduction in the tension in the pulsar noise parameters. As part of this reanalysis, we "extended" each PTA's data set by adding extra pulsars that were not timed by that PTA. Under these extensions, we find better constraints on the GWB amplitude and a higher signal-to-noise ratio for the Hellings and Downs correlations. These extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the IPTA, i.e., the IPTA's Data Release 3, which will involve not just adding in additional pulsars, but also including data from all three PTAs where any given pulsar is timed by more than as single PTA., Comment: 21 pages, 9 figures, submitted to ApJ
Published: 2023

6. Searching for continuous Gravitational Waves in the second data release of the International Pulsar Timing Array

Author: Falxa, M., Babak, S., Baker, P. T., Bécsy, B., Chalumeau, A., Chen, S., Chen, Z., Cornish, N. J., Guillemot, L., Hazboun, J. S., Mingarelli, C. M. F., Parthasarathy, A., Petiteau, A., Pol, N. S., Sesana, A., Spolaor, S. B., Taylor, S. R., Theureau, G., Vallisneri, M., Vigeland, S. J., Witt, C. A., Zhu, X., Antoniadis, J., Arzoumanian, Z., Bailes, M., Bhat, N. D. R., Blecha, L., Brazier, A., Brook, P. R., Caballero, N., Cameron, A. D., Casey-Clyde, J. A., Champion, D., Charisi, M., Chatterjee, S., Cognard, I., Cordes, J. M., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Feng, Y., Ferrara, E. C., Fiore, W., Fonseca, E., Garver-Daniels, N., Glaser, J., Goncharov, B., Good, D. C., Griessmeier, J., Guo, Y. J., Gültekin, K., Hobbs, G., Hu, H., Islo, K., Jang, J., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaczmarek, J., Kaiser, A. R., Kaplan, D. L., Keith, M., Kelley, L. Z., Kerr, M., Key, J. S., Laal, N., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Liu, K., Liu, T., Luo, J., Lynch, R. S., Madison, D. R., Main, R., Manchester, R., McEwen, A., McKee, J., McLaughlin, M. A., Ng, C., Nice, D. J., Ocker, S., Olum, K. D., Osłowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Porayko, N., Possenti, A., Quelquejay-Leclere, H., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sarkissian, J., Schult, L., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J. J., Siwek, M., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B., Stinebring, D. R., Swiggum, J. K., Tiburzi, C., Turner, J., Vecchio, A., Verbiest, J. P. W., Wahl, H., Wang, S. Q., Wang, J., Wu, Z., Zhang, L., and Zhang, S.
Subjects: General Relativity and Quantum Cosmology, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The International Pulsar Timing Array 2nd data release is the combination of datasets from worldwide collaborations. In this study, we search for continuous waves: gravitational wave signals produced by individual supermassive black hole binaries in the local universe. We consider binaries on circular orbits and neglect the evolution of orbital frequency over the observational span. We find no evidence for such signals and set sky averaged 95% upper limits on their amplitude h 95 . The most sensitive frequency is 10nHz with h 95 = 9.1 10-15 . We achieved the best upper limit to date at low and high frequencies of the PTA band thanks to improved effective cadence of observations. In our analysis, we have taken into account the recently discovered common red noise process, which has an impact at low frequencies. We also find that the peculiar noise features present in some pulsars data must be taken into account to reduce the false alarm. We show that using custom noise models is essential in searching for continuous gravitational wave signals and setting the upper limit.
Published: 2023
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7. Revealing the Dynamic Magneto-ionic Environments of Repeating Fast Radio Burst Sources through Multi-year Polarimetric Monitoring with CHIME/FRB

Author: Mckinven, R., Gaensler, B. M., Michilli, D., Masui, K., Kaspi, V. M., Su, J., Bhardwaj, M., Cassanelli, T., Chawla, P., Dong, Fonseca, E., Leung, C., Petroff, E., Pleunis, Z., Rafiei-Ravandi, M., Stairs, I. H., Tendulkar, S., Li, D. Z., Ng, C., Patel, C., Pearlman, A. B., Rahman, M., Sand, K. R., and Shin, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Fast radio bursts (FRBs) display a confounding variety of burst properties and host galaxy associations. Repeating FRBs offer insight into the FRB population by enabling spectral, temporal and polarimetric properties to be tracked over time. Here, we report on the polarized observations of 12 repeating sources using multi-year monitoring with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) over 400-800 MHz. We observe significant RM variations from many sources in our sample, including RM changes of several hundred $\rm{rad\, m^{-2}}$ over month timescales from FRBs 20181119A, 20190303A and 20190417A, and more modest RM variability ($\rm{\Delta RM \lesssim}$ few tens rad m$^{-2}$) from FRBs 20181030A, 20190208A, 20190213B and 20190117A over equivalent timescales. Several repeaters display a frequency dependent degree of linear polarization that is consistent with depolarization via scattering. Combining our measurements of RM variations with equivalent constraints on DM variability, we estimate the average line-of-sight magnetic field strength in the local environment of each repeater. In general, repeating FRBs display RM variations that are more prevalent/extreme than those seen from radio pulsars in the Milky Way and the Magellanic Clouds, suggesting repeating FRBs and pulsars occupy distinct magneto-ionic environments.
Published: 2023
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8. Gravitational signal propagation in the Double Pulsar studied with the MeerKAT telescope

Author: Hu, H., Kramer, M., Champion, D. J., Wex, N., Parthasarathy, A., Pennucci, T. T., Porayko, N. K., van Straten, W., Krishnan, V. Venkatraman, Burgay, M., Freire, P. C. C., Manchester, R. N., Possenti, A., Stairs, I. H., Bailes, M., Buchner, S., Cameron, A. D., Camilo, F., and Serylak, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics, General Relativity and Quantum Cosmology
Abstract: The Double Pulsar, PSR J0737-3039A/B, has offered a wealth of gravitational experiments in the strong-field regime, all of which GR has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the Double Pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in future, the SKA can greatly improve the accuracy of current tests and facilitate tests of NLO contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737-3039A, made using the MeerKAT telescope over the last 3 years. The increased timing precision offered by MeerKAT yields a 2 times better measurement of Shapiro delay parameter s and improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16-yr data by a factor of 1.65. These effects include the retardation effect due to the movement of B and the deflection of the signal by the gravitational field of B. We also investigate novel effects which are expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line-of-sight due to latitudinal signal deflection and find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the Double Pulsar system that meets the timing precision expected from future instruments such as the full SKA., Comment: 13 pages, 13 figures, accepted for publication in A&A
Published: 2022
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9. CHIME Discovery of a Binary Pulsar with a Massive Non-Degenerate Companion

Author: Andersen, Bridget C., Fonseca, Emmanuel, McKee, J. W., Meyers, B. W., Luo, Jing, Tan, C. M., Stairs, I. H., Kaspi, Victoria M., van Kerkwijk, M. H., Bhardwaj, Mohit, Boyle, P. J., Crowter, Kathryn, Demorest, Paul B., Dong, Fengqui A., Good, Deborah C., Kaczmarek, Jane F., Leung, Calvin, Masui, Kiyoshi W., Naidu, Arun, Ng, Cherry, Patel, Chitrang, Pearlman, Aaron B., Pleunis, Ziggy, Rafiei-Ravandi, Masoud, Rahman, Mubdi, Ransom, Scott M., Smith, Kendrick M., and Tendulkar, Shriharsh P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Of the more than $3{,}000$ radio pulsars currently known, only ${\sim}300$ are in binary systems, and only five of these consist of young pulsars with massive non-degenerate companions. We present the discovery and initial timing, accomplished using the Canadian Hydrogen Intensity Mapping Experiment telescope (CHIME), of the sixth such binary pulsar, PSR J2108+4516, a $0.577$-s radio pulsar in a 269-day orbit of eccentricity 0.09 with a companion of minimum mass $11$ M$_{\odot}$. Notably, the pulsar undergoes periods of substantial eclipse, disappearing from the CHIME $400{-}800$ MHz observing band for a large fraction of its orbit, and displays significant dispersion measure and scattering variations throughout its orbit, pointing to the possibility of a circumstellar disk or very dense stellar wind associated with the companion star. Subarcsecond resolution imaging with the Karl G. Jansky Very Large Array unambiguously demonstrates that the companion is a bright, $V \simeq 11$ OBe star, EM* UHA 138, located at a distance of $3.26(14)$ kpc. Archival optical observations of \companion{} approximately suggest a companion mass ranging from $17.5$ M$_{\odot} < M_{\rm c} < 23$ M$_{\odot}$, in turn constraining the orbital inclination angle to $50.3^{\circ} \lesssim i \lesssim 58.3^{\circ}$. With further multi-wavelength followup, PSR J2108+4516 promises to serve as another rare laboratory for the exploration of companion winds, circumstellar disks, and short-term evolution through extended-body orbital dynamics., Comment: 20 pages, 12 figures, accepted by ApJ
Published: 2022
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10. A Large Scale Magneto-ionic Fluctuation in the Local Environment of Periodic Fast Radio Burst Source, FRB 20180916B

Author: Mckinven, R., Gaensler, B. M., Michilli, D., Masui, K., Kaspi, V. M., Bhardwaj, M., Cassanelli, T., Chawla, P., Dong, F. Adam, Fonseca, E., Leung, C., Li, D. Z., Ng, C., Patel, C., Petroff, E., Pearlman, A. B., Pleunis, Z., Rafiei-Ravandi, M., Rahman, M., Sand, K. R., Shin, K., Scholz, P., Stairs, I. H., Smith, K., Su, J., and Tendulkar, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Fast radio burst (FRB) source 20180916B exhibits a 16.33-day periodicity in its burst activity. It is as of yet unclear what proposed mechanism produces the activity, but polarization information is a key diagnostic. Here, we report on the polarization properties of 44 bursts from FRB 20180916B detected between 2018 December and 2021 December by CHIME/FRB, the FRB project on the Canadian Hydrogen Intensity Mapping Experiment the Canadian Hydrogen Intensity Mapping Experiment. In contrast to previous observations, we find significant variations in the Faraday rotation measure (RM) of FRB 20180916B. Over the nine month period 2021 April$-$2021 December we observe an apparent secular increase in $\rm{RM}$ of $\sim 50 \; \rm{rad\, m^{-2}}$ (a fractional change of over $40\%$) that is accompanied by a possible drift of the emitting band to lower frequencies. This interval displays very little variation in the dispersion measure ($\Delta \rm{DM}\lesssim 0.8\; \rm{pc\, cm^{-3}}$) which indicates that the observed RM evolution is likely produced from coherent changes in the Faraday-active medium's magnetic field. Burst-to-burst RM variations appear unrelated to the activity cycle phase. The degree of linear polarization of our burst sample ($\gtrsim 80\%$) is consistent with the negligible depolarization expected for this source in the 400-800 MHz bandpass of CHIME. FRB 20180916B joins other repeating FRBs in displaying substantial RM variations between bursts. This is consistent with the notion that repeater progenitors may be associated with young stellar populations by their preferential occupation of dynamic magnetized environments commonly found in supernova remnants, pulsar wind nebulae or near high mass stellar companions.
Published: 2022
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11. Non-detection of CHIME/FRB sources with the Arecibo Observatory

Author: Good, Deborah C., Chawla, Pragya, Fonseca, Emmanuel, Kaspi, Victoria, Meyers, B. W., Pleunis, Ziggy, Sand, Ketan R., Scholz, Paul, Stairs, I. H., and Tendulkar, Shriharsh P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: In this work, we present follow-up observations of two known repeating fast radio bursts (FRBs) and seven non-repeating FRBs with complex morphology discovered with CHIME/FRB. These observations were conducted with the Arecibo Observatory 327 MHz receiver. We detected no additional bursts from these sources, nor did CHIME/FRB detect any additional bursts from these sources during our follow-up program. Based on these non-detections, we provide constraints on the repetition rate, for all nine sources. We calculate repetition rates above 1 Jy using both a Poisson distribution of repetition and the Weibull distribution of repetition presented by Oppermann et al. (2018). For both distributions, we find repetition upper limits of the order $\lambda = 10^{-2} - 10^{-1} \text{hr}^{-1}$ for all sources. These rates are much lower than those recently published for notable repeating FRBs like FRB 20121102A and FRB 20201124A, suggesting the possibility of a low-repetition sub-population., Comment: 12 pages, 4 figures, 5 tables
Published: 2022
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12. Discoveries and Timing of Pulsars in NGC 6440

Author: Vleeschower, L., Stappers, B. W., Bailes, M., Barr, E. D., Kramer, M., Ransom, S., Ridolfi, A., Krishnan, V. Venkatraman, Possenti, A., Keith, M. J., Burgay, M., Freire, P. C. C., Spiewak, R., Champion, D. J., Bezuidenhout, M. C., Niţu, I. C., Chen, W., Parthasarathy, A., DeCesar, M. E., Buchner, S., Stairs, I. H., and Hessels, J. W. T.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract: Using the MeerKAT radio telescope, a series of observations have been conducted to time the known pulsars and search for new pulsars in the globular cluster NGC 6440. As a result, two pulsars have been discovered, NGC 6440G and NGC 6440H, one of which is isolated and the other a non-eclipsing (at frequencies above 962 MHz) "Black Widow", with a very low mass companion (M$_{\rm c}$ > 0.006 M$_{\odot}$). It joins the other binary pulsars discovered so far in this cluster which all have low companion masses (M$_{\rm c}$ < 0.30 M$_{\odot}$). We present the results of long-term timing solutions obtained using data from both Green Bank and MeerKAT telescopes for these two new pulsars and an analysis of the pulsars NGC 6440C and NGC 6440D. For the isolated pulsar NGC 6440C, we searched for planets using a Markov Chain Monte Carlo technique. We find evidence for significant unmodelled variations but they cannot be well modelled as planets nor as part of a power-law red-noise process. Studies of the eclipses of the "Redback" pulsar NGC 6440D at two different frequency bands reveal a frequency dependence with longer and asymmetric eclipses at lower frequencies (962-1283 MHz)., Comment: 14 pages, 10 figures, 4 tables. Accepted for publication in MNRAS
Published: 2022
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13. The eccentric millisecond pulsar, PSR J0955$-$6150 I: Pulse profile analysis, mass measurements and constraints on binary evolution

Author: Serylak, M., Krishnan, V. Venkatraman, Freire, P. C. C., Tauris, T. M., Kramer, M., Geyer, M., Parthasarathy, A., Bailes, M., Bernadich, M. C. i, Buchner, S., Burgay, M., Camilo, F., Karastergiou, A., Lower, M. E., Possenti, A., Reardon, D. J., Shannon, R. M., Spiewak, R., Stairs, I. H., and van Straten, W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: PSR J0955$-$6150 is a member of a class of eccentric MSP+He WD systems (eMSPs), whose binary evolution is poorly understood and believed to be different to that of traditional MSP+He WD systems. Measuring the masses of the stars in this system is important for testing hypotheses for the formation of eMSPs. We have carried out observations of this pulsar with the Parkes and MeerKAT radio telescopes. Our observations reveal a strong frequency evolution of this pulsar's intensity, with a spectral index ($\alpha$) of $-3.13(2)$. The sensitivity of MeerKAT has resulted in a $>10$-fold improvement in the timing precision compared to older Parkes observations. Combined with the 8-year timing baseline, it has allowed precise measurements of a proper motion and three orbital "post-Keplerian" parameters: the rate of advance of periastron, $\dot{\omega} = 0.00152(1) \, {\rm deg} \, yr^{-1}$ and the orthometric Shapiro delay parameters, $h_3 = 0.89(7) \, \mu$s and $\varsigma = 0.88(2)$. Assuming general relativity, we obtain $M_{p} = 1.71(2) \, M_{\odot}$ for the mass of the pulsar and $M_{c} = 0.254(2) \, M_{\odot}$ for the mass of the companion; the orbital inclination is 83.2(4) degrees. We find that the spin axis has a misalignment relative to the orbital angular momentum of $> 4.8$ degrees at 99% CI. While the value of $M_{\rm p}$ falls within the wide range observed in eMSPs, $M_{\rm c}$ is significantly smaller than expected, allowing several formation hypotheses being ruled out. $M_{\rm c}$ is also significantly different from the expected value for an ideal low mass X-ray binary evolution scenario. The putative misalignment between the spin axis of the pulsar and the orbital angular momentum suggests that the unknown process that created the orbital eccentricity of the binary was also capable of changing its orbital orientation, an important evidence for understanding the origin of eMSPs., Comment: 20 pages, 9 figures, 5 tables, accepted for publication by the A&A
Published: 2022
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14. The International Pulsar Timing Array second data release: Search for an isotropic Gravitational Wave Background

Author: Antoniadis, J., Arzoumanian, Z., Babak, S., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Becsy, B., Berthereau, A., Bonetti, M., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Casey-Clyde, J. A., Chalumeau, A., Champion, D. J., Charisi, M., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Falxa, M., Ferrara, E. C., Fiore, W., Fonseca, E., Gair, J. R., Garver-Daniels, N., Goncharov, B., Good, D. C., Graikou, E., Guillemot, L., Guo, Y. J., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Karuppusamy, R., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kramer, M., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Lee, K. J., Lentati, L., Liu, K., Luo, J., Lynch, R. S., Lyne, A. G., Madison, D. R., Main, R. A., Manchester, R. N., McEwen, A., McKee, J. W., McLaughlin, M. A., Mickaliger, M. B., Mingarelli, C. M. F., Ng, C., Nice, D. J., lowski, S. Os, Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Pol, N. S., Porayko, N. K., Possenti, A., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sampson, L. M., Sanidas, S., Sarkissian, J. M., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., van der Wateren, E., Vecchio, A., Verbiest, J. P. W., Vigeland, S. J., Wahl, H., Wang, J. B., Wang, J., Wang, L., Witt, C. A., Zhang, S., and Zhu, X. J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We searched for an isotropic stochastic gravitational wave background in the second data release of the International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns in North America, Europe, and Australia. In our reference search for a power law strain spectrum of the form $h_c = A(f/1\,\mathrm{yr}^{-1})^{\alpha}$, we found strong evidence for a spectrally-similar low-frequency stochastic process of amplitude $A = 3.8^{+6.3}_{-2.5}\times10^{-15}$ and spectral index $\alpha = -0.5 \pm 0.5$, where the uncertainties represent 95\% credible regions, using information from the auto- and cross-correlation terms between the pulsars in the array. For a spectral index of $\alpha = -2/3$, as expected from a population of inspiralling supermassive black hole binaries, the recovered amplitude is $A = 2.8^{+1.2}_{-0.8}\times10^{-15}$. Nonetheless, no significant evidence of the Hellings-Downs correlations that would indicate a gravitational-wave origin was found. We also analyzed the constituent data from the individual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. Furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. Future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability., Comment: 17 pages, 12 figures, accepted in MNRAS
Published: 2022
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15. Narrowband searches for continuous and long-duration transient gravitational waves from known pulsars in the LIGO-Virgo third observing run

Author: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, Abbott, R., Abbott, T. D., Acernese, F., Ackley, K., Adams, C., Adhikari, N., Adhikari, R. X., Adya, V. B., Affeldt, C., Agarwal, D., Agathos, M., Agatsuma, K., Aggarwal, N., Aguiar, O. D., Aiello, L., Ain, A., Ajith, P., Akutsu, T., Albanesi, S., Allocca, A., Altin, P. A., Amato, A., Anand, C., Anand, S., Ananyeva, A., Anderson, S. B., Anderson, W. G., Ando, M., Andrade, T., Andres, N., Andrić, T., Angelova, S. V., Ansoldi, S., Antelis, J. M., Antier, S., Appert, S., Arai, Koji, Arai, Koya, Arai, Y., Araki, S., Araya, A., Araya, M. C., Areeda, J. S., Arène, M., Aritomi, N., Arnaud, N., Aronson, S. M., Arun, K. G., Asada, H., Asali, Y., Ashton, G., Aso, Y., Assiduo, M., Aston, S. M., Astone, P., Aubin, F., Austin, C., Babak, S., Badaracco, F., Bader, M. K. M., Badger, C., Bae, S., Bae, Y., Baer, A. M., Bagnasco, S., Bai, Y., Bailes, M., Baiotti, L., Baird, J., Bajpai, R., Ball, M., Ballardin, G., Ballmer, S. W., Balsamo, A., Baltus, G., Banagiri, S., Bankar, D., Barayoga, J. C., Barbieri, C., Barish, B. C., Barker, D., Barneo, P., Barone, F., Barr, B., Barsotti, L., Barsuglia, M., Barta, D., Bartlett, J., Barton, M. A., Bartos, I., Bassiri, R., Basti, A., Bawaj, M., Bayley, J. C., Baylor, A. C., Bazzan, M., Bécsy, B., Bedakihale, V. M., Bejger, M., Belahcene, I., Benedetto, V., Beniwal, D., Bennett, T. F., Bentley, J. D., BenYaala, M., Bergamin, F., Berger, B. K., Bernuzzi, S., Bersanetti, D., Bertolini, A., Betzwieser, J., Beveridge, D., Bhandare, R., Bhardwaj, U., Bhattacharjee, D., Bhaumik, S., Bilenko, I. A., Billingsley, G., Bini, S., Birney, R., Birnholtz, O., Biscans, S., Bischi, M., Biscoveanu, S., Bisht, A., Biswas, B., Bitossi, M., Bizouard, M. -A., Blackburn, J. K., Blair, C. D., Blair, D. G., Blair, R. M., Bobba, F., Bode, N., Boer, M., Bogaert, G., Boldrini, M., Bonavena, L. D., Bondu, F., Bonilla, E., Bonnand, R., Booker, P., Boom, B. A., Bork, R., Boschi, V., Bose, N., Bose, S., Bossilkov, V., Boudart, V., Bouffanais, Y., Bozzi, A., Bradaschia, C., Brady, P. R., Bramley, A., Branch, A., Branchesi, M., Brau, J. E., Breschi, M., Briant, T., Briggs, J. H., Brillet, A., Brinkmann, M., Brockill, P., Brooks, A. F., Brooks, J., Brown, D. D., Brunett, S., Bruno, G., Bruntz, R., Bryant, J., Bulik, T., Bulten, H. J., Buonanno, A., Buscicchio, R., Buskulic, D., Buy, C., Byer, R. L., Cadonati, L., Cagnoli, G., Cahillane, C., Bustillo, J. Calderón, Callaghan, J. D., Callister, T. A., Calloni, E., Cameron, J., Camp, J. B., Canepa, M., Canevarolo, S., Cannavacciuolo, M., Cannon, K. C., Cao, H., Cao, Z., Capocasa, E., Capote, E., Carapella, G., Carbognani, F., Carlin, J. B., Carney, M. F., Carpinelli, M., Carrillo, G., Carullo, G., Carver, T. L., Diaz, J. Casanueva, Casentini, C., Castaldi, G., Caudill, S., Cavaglià, M., Cavalier, F., Cavalieri, R., Ceasar, M., Cella, G., Cerdá-Durán, P., Cesarini, E., Chaibi, W., Chakravarti, K., Subrahmanya, S. Chalathadka, Champion, E., Chan, C. -H., Chan, C., Chan, C. L., Chan, K., Chan, M., Chandra, K., Chanial, P., Chao, S., Charlton, P., Chase, E. A., Chassande-Mottin, E., Chatterjee, C., Chatterjee, Debarati, Chatterjee, Deep, Chaturvedi, M., Chaty, S., Chen, C., Chen, H. Y., Chen, J., Chen, K., Chen, X., Chen, Y. -B., Chen, Y. -R., Chen, Z., Cheng, H., Cheong, C. K., Cheung, H. Y., Chia, H. Y., Chiadini, F., Chiang, C-Y., Chiarini, G., Chierici, R., Chincarini, A., Chiofalo, M. L., Chiummo, A., Cho, G., Cho, H. S., Choudhary, R. K., Choudhary, S., Christensen, N., Chu, H., Chu, Q., Chu, Y-K., Chua, S., Chung, K. W., Ciani, G., Ciecielag, P., Cieślar, M., Cifaldi, M., Ciobanu, A. A., Ciolfi, R., Cipriano, F., Cirone, A., Clara, F., Clark, E. N., Clark, J. A., Clarke, L., Clearwater, P., Clesse, S., Cleva, F., Coccia, E., Codazzo, E., Cohadon, P. -F., Cohen, D. E., Cohen, L., Colleoni, M., Collette, C. G., Colombo, A., Colpi, M., Compton, C. M., Constancio Jr., M., Conti, L., Cooper, S. J., Corban, P., Corbitt, T. R., Cordero-Carrión, I., Corezzi, S., Corley, K. R., Cornish, N., Corre, D., Corsi, A., Cortese, S., Costa, C. A., Cotesta, R., Coughlin, M. W., Coulon, J. -P., Countryman, S. T., Cousins, B., Couvares, P., Coward, D. M., Cowart, M. J., Coyne, D. C., Coyne, R., Creighton, J. D. E., Creighton, T. D., Criswell, A. W., Croquette, M., Crowder, S. G., Cudell, J. R., Cullen, T. J., Cumming, A., Cummings, R., Cunningham, L., Cuoco, E., Curyło, M., Dabadie, P., Canton, T. Dal, Dall'Osso, S., Dálya, G., Dana, A., DaneshgaranBajastani, L. M., D'Angelo, B., Danilishin, S., D'Antonio, S., Danzmann, K., Darsow-Fromm, C., Dasgupta, A., Datrier, L. E. H., Datta, S., Dattilo, V., Dave, I., Davier, M., Davies, G. S., Davis, D., Davis, M. C., Daw, E. J., Dean, R., DeBra, D., Deenadayalan, M., Degallaix, J., De Laurentis, M., Deléglise, S., Del Favero, V., De Lillo, F., De Lillo, N., Del Pozzo, W., DeMarchi, L. M., De Matteis, F., D'Emilio, V., Demos, N., Dent, T., Depasse, A., De Pietri, R., De Rosa, R., De Rossi, C., DeSalvo, R., De Simone, R., Dhurandhar, S., Díaz, M. C., Diaz-Ortiz Jr., M., Didio, N. A., Dietrich, T., Di Fiore, L., Di Fronzo, C., Di Giorgio, C., Di Giovanni, F., Di Giovanni, M., Di Girolamo, T., Di Lieto, A., Ding, B., Di Pace, S., Di Palma, I., Di Renzo, F., Divakarla, A. K., Dmitriev, A., Doctor, Z., D'Onofrio, L., Donovan, F., Dooley, K. L., Doravari, S., Dorrington, I., Drago, M., Driggers, J. C., Drori, Y., Ducoin, J. -G., Dupej, P., Durante, O., D'Urso, D., Duverne, P. -A., Dwyer, S. E., Eassa, C., Easter, P. J., Ebersold, M., Eckhardt, T., Eddolls, G., Edelman, B., Edo, T. B., Edy, O., Effler, A., Eguchi, S., Eichholz, J., Eikenberry, S. S., Eisenmann, M., Eisenstein, R. A., Ejlli, A., Engelby, E., Enomoto, Y., Errico, L., Essick, R. C., Estellés, H., Estevez, D., Etienne, Z., Etzel, T., Evans, M., Evans, T. M., Ewing, B. E., Fafone, V., Fair, H., Fairhurst, S., Farah, A. M., Farinon, S., Farr, B., Farr, W. M., Farrow, N. W., Fauchon-Jones, E. J., Favaro, G., Favata, M., Fays, M., Fazio, M., Feicht, J., Fejer, M. M., Fenyvesi, E., Ferguson, D. L., Fernandez-Galiana, A., Ferrante, I., Ferreira, T. A., Fidecaro, F., Figura, P., Fiori, I., Fishbach, M., Fisher, R. P., Fittipaldi, R., Fiumara, V., Flaminio, R., Floden, E., Fong, H., Font, J. A., Fornal, B., Forsyth, P. W. F., Franke, A., Frasca, S., Frasconi, F., Frederick, C., Freed, J. P., Frei, Z., Freise, A., Frey, R., Fritschel, P., Frolov, V. V., Fronzé, G. G., Fujii, Y., Fujikawa, Y., Fukunaga, M., Fukushima, M., Fulda, P., Fyffe, M., Gabbard, H. A., Gadre, B. U., Gair, J. R., Gais, J., Galaudage, S., Gamba, R., Ganapathy, D., Ganguly, A., Gao, D., Gaonkar, S. G., Garaventa, B., García-Núñez, C., García-Quirós, C., Garufi, F., Gateley, B., Gaudio, S., Gayathri, V., Ge, G. -G., Gemme, G., Gennai, A., George, J., Gerberding, O., Gergely, L., Gewecke, P., Ghonge, S., Ghosh, Abhirup, Ghosh, Archisman, Ghosh, Shaon, Ghosh, Shrobana, Giacomazzo, B., Giacoppo, L., Giaime, J. A., Giardina, K. D., Gibson, D. R., Gier, C., Giesler, M., Giri, P., Gissi, F., Glanzer, J., Gleckl, A. E., Godwin, P., Goetz, E., Goetz, R., Gohlke, N., Goncharov, B., González, G., Gopakumar, A., Gosselin, M., Gouaty, R., Gould, D. W., Grace, B., Grado, A., Granata, M., Granata, V., Grant, A., Gras, S., Grassia, P., Gray, C., Gray, R., Greco, G., Green, A. C., Green, R., Gretarsson, A. M., Gretarsson, E. M., Griffith, D., Griffiths, W., Griggs, H. L., Grignani, G., Grimaldi, A., Grimm, S. J., Grote, H., Grunewald, S., Gruning, P., Guerra, D., Guidi, G. M., Guimaraes, A. R., Guixé, G., Gulati, H. K., Guo, H. -K., Guo, Y., Gupta, Anchal, Gupta, Anuradha, Gupta, P., Gustafson, E. K., Gustafson, R., Guzman, F., Ha, S., Haegel, L., Hagiwara, A., Haino, S., Halim, O., Hall, E. D., Hamilton, E. Z., Hammond, G., Han, W. -B., Haney, M., Hanks, J., Hanna, C., Hannam, M. D., Hannuksela, O., Hansen, H., Hansen, T. J., Hanson, J., Harder, T., Hardwick, T., Haris, K., Harms, J., Harry, G. M., Harry, I. W., Hartwig, D., Hasegawa, K., Haskell, B., Hasskew, R. K., Haster, C. -J., Hattori, K., Haughian, K., Hayakawa, H., Hayama, K., Hayes, F. J., Healy, J., Heidmann, A., Heidt, A., Heintze, M. C., Heinze, J., Heinzel, J., Heitmann, H., Hellman, F., Hello, P., Helmling-Cornell, A. F., Hemming, G., Hendry, M., Heng, I. S., Hennes, E., Hennig, J., Hennig, M. H., Hernandez, A. G., Vivanco, F. Hernandez, Heurs, M., Hild, S., Hill, P., Himemoto, Y., Hines, A. S., Hiranuma, Y., Hirata, N., Hirose, E., Ho, W. C. G., Hochheim, S., Hofman, D., Hohmann, J. N., Holcomb, D. G., Holland, N. A., Hollows, I. J., Holmes, Z. J., Holt, K., Holz, D. E., Hong, Z., Hopkins, P., Hough, J., Hourihane, S., Howell, E. J., Hoy, C. G., Hoyland, D., Hreibi, A., Hsieh, B-H., Hsu, Y., Huang, G-Z., Huang, H-Y., Huang, P., Huang, Y-C., Huang, Y. -J., Huang, Y., Hübner, M. T., Huddart, A. D., Hughey, B., Hui, D. C. Y., Hui, V., Husa, S., Huttner, S. H., Huxford, R., Huynh-Dinh, T., Ide, S., Idzkowski, B., Iess, A., Ikenoue, B., Imam, S., Inayoshi, K., Ingram, C., Inoue, Y., Ioka, K., Isi, M., Isleif, K., Ito, K., Itoh, Y., Iyer, B. R., Izumi, K., JaberianHamedan, V., Jacqmin, T., Jadhav, S. J., Jadhav, S. P., James, A. L., Jan, A. Z., Jani, K., Janquart, J., Janssens, K., Janthalur, N. N., Jaranowski, P., Jariwala, D., Jaume, R., Jenkins, A. C., Jenner, K., Jeon, C., Jeunon, M., Jia, W., Jin, H. -B., Johns, G. R., Jones, A. W., Jones, D. I., Jones, J. D., Jones, P., Jones, R., Jonker, R. J. G., Ju, L., Jung, P., Jung, k., Junker, J., Juste, V., Kaihotsu, K., Kajita, T., Kakizaki, M., Kalaghatgi, C. V., Kalogera, V., Kamai, B., Kamiizumi, M., Kanda, N., Kandhasamy, S., Kang, G., Kanner, J. B., Kao, Y., Kapadia, S. J., Kapasi, D. P., Karat, S., Karathanasis, C., Karki, S., Kashyap, R., Kasprzack, M., Kastaun, W., Katsanevas, S., Katsavounidis, E., Katzman, W., Kaur, T., Kawabe, K., Kawaguchi, K., Kawai, N., Kawasaki, T., Kéfélian, F., Keitel, D., Key, J. S., Khadka, S., Khalili, F. Y., Khan, S., Khazanov, E. A., Khetan, N., Khursheed, M., Kijbunchoo, N., Kim, C., Kim, J. C., Kim, J., Kim, K., Kim, W. S., Kim, Y. -M., Kimball, C., Kimura, N., Kinley-Hanlon, M., Kirchhoff, R., Kissel, J. S., Kita, N., Kitazawa, H., Kleybolte, L., Klimenko, S., Knee, A. M., Knowles, T. D., Knyazev, E., Koch, P., Koekoek, G., Kojima, Y., Kokeyama, K., Koley, S., Kolitsidou, P., Kolstein, M., Komori, K., Kondrashov, V., Kong, A. K. H., Kontos, A., Koper, N., Korobko, M., Kotake, K., Kovalam, M., Kozak, D. B., Kozakai, C., Kozu, R., Kringel, V., Krishnendu, N. V., Królak, A., Kuehn, G., Kuei, F., Kuijer, P., Kumar, A., Kumar, P., Kumar, Rahul, Kumar, Rakesh, Kume, J., Kuns, K., Kuo, C., Kuo, H-S., Kuromiya, Y., Kuroyanagi, S., Kusayanagi, K., Kuwahara, S., Kwak, K., Lagabbe, P., Laghi, D., Lalande, E., Lam, T. L., Lamberts, A., Landry, M., Lane, B. B., Lang, R. N., Lange, J., Lantz, B., La Rosa, I., Lartaux-Vollard, A., Lasky, P. D., Laxen, M., Lazzarini, A., Lazzaro, C., Leaci, P., Leavey, S., Lecoeuche, Y. K., Lee, H. K., Lee, H. M., Lee, H. W., Lee, J., Lee, K., Lee, R., Lehmann, J., Lemaître, A., Leonardi, M., Leroy, N., Letendre, N., Levesque, C., Levin, Y., Leviton, J. N., Leyde, K., Li, A. K. Y., Li, B., Li, J., Li, K. L., Li, T. G. F., Li, X., Lin, C-Y., Lin, F-K., Lin, F-L., Lin, H. L., Lin, L. C. -C., Linde, F., Linker, S. D., Linley, J. N., Littenberg, T. B., Liu, G. C., Liu, J., Liu, K., Liu, X., Llamas, F., Llorens-Monteagudo, M., Lo, R. K. L., Lockwood, A., London, L. T., Longo, A., Lopez, D., Portilla, M. 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Subjects: General Relativity and Quantum Cosmology, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully-coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow the frequency and frequency time-derivative of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets., Comment: 37 pages, 9 figures, submitted to ApJ
Published: 2021
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16. Strong-field Gravity Tests with the Double Pulsar

Author: Kramer, M., Stairs, I. H., Manchester, R. N., Wex, N., Deller, A. T., Coles, W. A., Ali, M., Burgay, M., Camilo, F., Cognard, I., Damour, T., Desvignes, G., Ferdman, R. D., Freire, P. C. C., Grondin, S., Guillemot, L., Hobbs, G. B., Janssen, G., Karuppusamy, R., Lorimer, D. R., Lyne, A. G., McKee, J. W., McLaughlin, M., Muench, L. E., Perera, B. B. P., Pol, N., Possenti, A., Sarkissian, J., Stappers, B. W., and Theureau, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: Continued observations of the Double Pulsar, PSR J0737-3039A/B, consisting of two radio pulsars (A and B) that orbit each other with a period of 2.45hr in a mildly eccentric (e=0.088) binary system, have led to large improvements in the measurement of relativistic effects in this system. With a 16-yr data span, the results enable precision tests of theories of gravity for strongly self-gravitating bodies and also reveal new relativistic effects that have been expected but are now observed for the first time. These include effects of light propagation in strong gravitational fields which are currently not testable by any other method. We observe retardation and aberrational light-bending that allow determination of the pulsar's spin direction. In total, we have detected seven post-Keplerian (PK) parameters, more than for any other binary pulsar. For some of these effects, the measurement precision is so high that for the first time we have to take higher-order contributions into account. These include contributions of A's effective mass loss (due to spin-down) to the observed orbital period decay, a relativistic deformation of the orbit, and effects of the equation of state of super-dense matter on the observed PK parameters via relativistic spin-orbit coupling. We discuss the implications of our findings, including those for the moment of inertia of neutron stars. We present the currently most precise test of general relativity's (GR's) quadrupolar description of gravitational waves, validating GR's prediction at a level of $1.3 \times 10^{-4}$ (95% conf.). We demonstrate the utility of the Double Pulsar for tests of alternative theories by focusing on two specific examples and discuss some implications for studies of the interstellar medium and models for the formation of the Double Pulsar. Finally, we provide context to other types of related experiments and prospects for the future., Comment: 56 pages, 23 Figures. Published by Physical Review X. Uploaded ArXiv version is authors' (pre-proof) version with abbreviated abstract. Resubmission for updated acknowledgement information. For final published version see https://link.aps.org/doi/10.1103/PhysRevX.11.041050
Published: 2021
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17. Searches for Gravitational Waves from Known Pulsars at Two Harmonics in the Second and Third LIGO-Virgo Observing Runs

Author: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, Abbott, R., Abe, H., Acernese, F., Ackley, K., Adhikari, N., Adhikari, R. X., Adkins, V. K., Adya, V. B., Affeldt, C., Agarwal, D., Agathos, M., Agatsuma, K., Aggarwal, N., Aguiar, O. D., Aiello, L., Ain, A., Ajith, P., Akutsu, T., Albanesi, S., Alfaidi, R. A., Allocca, A., Altin, P. A., Amato, A., Anand, C., Anand, S., Ananyeva, A., Anderson, S. B., Anderson, W. G., Ando, M., Andrade, T., Andres, N., Andrés-Carcasona, M., Andrić, T., Angelova, S. V., Ansoldi, S., Antelis, J. M., Antier, S., Apostolatos, T., Appavuravther, E. Z., Appert, S., Apple, S. K., Arai, K., Araya, A., Araya, M. C., Areeda, J. S., Arène, M., Aritomi, N., Arnaud, N., Arogeti, M., Aronson, S. M., Arun, K. G., Asada, H., Asali, Y., Ashton, G., Aso, Y., Assiduo, M., Melo, S. Assis de Souza, Aston, S. M., Astone, P., Aubin, F., AultONeal, K., Austin, C., Babak, S., Badaracco, F., Bader, M. K. M., Badger, C., Bae, S., Bae, Y., Baer, A. M., Bagnasco, S., Bai, Y., Bailes, M., Baird, J., Bajpai, R., Baka, T., Ball, M., Ballardin, G., Ballmer, S. W., Balsamo, A., Baltus, G., Banagiri, S., Banerjee, B., Bankar, D., Barayoga, J. C., Barbieri, C., Barish, B. C., Barker, D., Barneo, P., Barone, F., Barr, B., Barsotti, L., Barsuglia, M., Barta, D., Bartlett, J., Barton, M. A., Bartos, I., Basak, S., Bassiri, R., Basti, A., Bawaj, M., Bayley, J. C., Bazzan, M., Becher, B. R., Bécsy, B., Bedakihale, V. M., Beirnaert, F., Bejger, M., Belahcene, I., Benedetto, V., Beniwal, D., Benjamin, M. G., Bennett, T. F., Bentley, J. D., BenYaala, M., Bera, S., Berbel, M., Bergamin, F., Berger, B. K., Bernuzzi, S., Bersanetti, D., Bertolini, A., Betzwieser, J., Beveridge, D., Bhandare, R., Bhandari, A. V., Bhardwaj, U., Bhatt, R., Bhattacharjee, D., Bhaumik, S., Bianchi, A., Bilenko, I. 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A., Robie, R., Robinet, F., Rocchi, A., Rodriguez, S., Rolland, L., Rollins, J. G., Romanelli, M., Romano, R., Romel, C. L., Romero, A., Romero-Shaw, I. M., Romie, J. H., Ronchini, S., Rosa, L., Rose, C. A., Rosińska, D., Ross, M. P., Rowan, S., Rowlinson, S. J., Roy, S., Roy, Santosh, Roy, Soumen, Rozza, D., Ruggi, P., Ruiz-Rocha, K., Ryan, K., Sachdev, S., Sadecki, T., Sadiq, J., Saha, S., Saito, Y., Sakai, K., Sakellariadou, M., Sakon, S., Salafia, O. S., Salces-Carcoba, F., Salconi, L., Saleem, M., Salemi, F., Samajdar, A., Sanchez, E. J., Sanchez, J. H., Sanchez, L. E., Sanchis-Gual, N., Sanders, J. R., Sanuy, A., Saravanan, T. R., Sarin, N., Sassolas, B., Satari, H., Sauter, O., Savage, R. L., Savant, V., Sawada, T., Sawant, H. L., Sayah, S., Schaetzl, D., Scheel, M., Scheuer, J., Schiworski, M. G., Schmidt, P., Schmidt, S., Schnabel, R., Schneewind, M., Schofield, R. M. S., Schönbeck, A., Schulte, B. W., Schutz, B. F., Schwartz, E., Scott, J., Scott, S. M., Seglar-Arroyo, M., Sekiguchi, Y., Sellers, D., Sengupta, A. S., Sentenac, D., Seo, E. G., Sequino, V., Sergeev, A., Setyawati, Y., Shaffer, T., Shahriar, M. S., Shaikh, M. A., Shams, B., Shao, L., Sharma, A., Sharma, P., Shawhan, P., Shcheblanov, N. S., Sheela, A., Shikano, Y., Shikauchi, M., Shimizu, H., Shimode, K., Shinkai, H., Shishido, T., Shoda, A., Shoemaker, D. H., Shoemaker, D. M., ShyamSundar, S., Sieniawska, M., Sigg, D., Silenzi, L., Singer, L. P., Singh, D., Singh, M. K., Singh, N., Singha, A., Sintes, A. M., Sipala, V., Skliris, V., Slagmolen, B. J. J., Slaven-Blair, T. J., Smetana, J., Smith, J. R., Smith, L., Smith, R. J. E., Soldateschi, J., Somala, S. N., Somiya, K., Song, I., Soni, K., Sordini, V., Sorrentino, F., Sorrentino, N., Soulard, R., Souradeep, T., Sowell, E., Spagnuolo, V., Spencer, A. P., Spera, M., Spinicelli, P., Srivastava, A. K., Srivastava, V., Staats, K., Stachie, C., Stachurski, F., Steer, D. A., Steinlechner, J., Steinlechner, S., Stergioulas, N., Stops, D. J., Stover, M., Strain, K. A., Strang, L. C., Stratta, G., Strong, M. D., Strunk, A., Sturani, R., Stuver, A. L., Suchenek, M., Sudhagar, S., Sudhir, V., Sugimoto, R., Suh, H. G., Sullivan, A. G., Summerscales, T. Z., Sun, L., Sunil, S., Sur, A., Suresh, J., Sutton, P. J., Suzuki, Takamasa, Suzuki, Takanori, Suzuki, Toshikazu, Swinkels, B. L., Szczepańczyk, M. J., Szewczyk, P., Tacca, M., Tagoshi, H., Tait, S. C., Takahashi, H., Takahashi, R., Takano, S., Takeda, H., Takeda, M., Talbot, C. J., Talbot, C., Tanaka, K., Tanaka, Taiki, Tanaka, Takahiro, Tanasijczuk, A. J., Tanioka, S., Tanner, D. B., Tao, D., Tao, L., Tapia, R. D., Martín, E. N. Tapia San, Taranto, C., Taruya, A., Tasson, J. D., Tenorio, R., Terhune, J. E. S., Terkowski, L., Thirugnanasambandam, M. P., Thomas, M., Thomas, P., Thompson, E. E., Thompson, J. E., Thondapu, S. R., Thorne, K. A., Thrane, E., Tiwari, Shubhanshu, Tiwari, Srishti, Tiwari, V., Toivonen, A. M., Tolley, A. E., Tomaru, T., Tomura, T., Tonelli, M., Tornasi, Z., Torres-Forné, A., Torrie, C. I., Melo, I. Tosta e, Töyrä, D., Trapananti, A., Travasso, F., Traylor, G., Trevor, M., Tringali, M. C., Tripathee, A., Troiano, L., Trovato, A., Trozzo, L., Trudeau, R. J., Tsai, D., Tsang, K. W., Tsang, T., Tsao, J-S., Tse, M., Tso, R., Tsuchida, S., Tsukada, L., Tsuna, D., Tsutsui, T., Turbang, K., Turconi, M., Tuyenbayev, D., Ubhi, A. S., Uchikata, N., Uchiyama, T., Udall, R. P., Ueda, A., Uehara, T., Ueno, K., Ueshima, G., Unnikrishnan, C. S., Urban, A. L., Ushiba, T., Utina, A., Vajente, G., Vajpeyi, A., Valdes, G., Valentini, M., Valsan, V., van Bakel, N., van Beuzekom, M., van Dael, M., Brand, J. F. J. van den, Broeck, C. Van Den, Vander-Hyde, D. C., van Haevermaet, H., van Heijningen, J. V., van Putten, M. H. P. M., van Remortel, N., Vardaro, M., Vargas, A. F., Varma, V., Vasúth, M., Vecchio, A., Vedovato, G., Veitch, J., Veitch, P. J., Venneberg, J., Venugopalan, G., Verkindt, D., Verma, P., Verma, Y., Vermeulen, S. M., Veske, D., Vetrano, F., Viceré, A., Vidyant, S., Viets, A. D., Vijaykumar, A., Villa-Ortega, V., Vinet, J. -Y., Virtuoso, A., Vitale, S., Vocca, H., von Reis, E. R. G., von Wrangel, J. S. A., Vorvick, C., Vyatchanin, S. P., Wade, L. E., Wade, M., Wagner, K. J., Walet, R. C., Walker, M., Wallace, G. S., Wallace, L., Wang, J., Wang, J. Z., Wang, W. H., Ward, R. L., Warner, J., Was, M., Washimi, T., Washington, N. Y., Watchi, J., Weaver, B., Weaving, C. R., Webster, S. A., Weinert, M., Weinstein, A. J., Weiss, R., Weller, C. M., Weller, R. A., Wellmann, F., Wen, L., Weßels, P., Wette, K., Whelan, J. T., White, D. D., Whiting, B. F., Whittle, C., Wilken, D., Williams, D., Williams, M. J., Williamson, A. R., Willis, J. L., Willke, B., Wilson, D. J., Wipf, C. C., Wlodarczyk, T., Woan, G., Woehler, J., Wofford, J. K., Wong, D., Wong, I. C. F., Wright, M., Wu, C., Wu, D. S., Wu, H., Wysocki, D. M., Xiao, L., Yamada, T., Yamamoto, H., Yamamoto, K., Yamamoto, T., Yamashita, K., Yamazaki, R., Yang, F. W., Yang, K. Z., Yang, L., Yang, Y. -C., Yang, Y., Yang, Yang, Yap, M. J., Yeeles, D. W., Yeh, S. -W., Yelikar, A. B., Ying, M., Yokoyama, J., Yokozawa, T., Yoo, J., Yoshioka, T., Yu, Hang, Yu, Haocun, Yuzurihara, H., Zadrożny, A., Zanolin, M., Zeidler, S., Zelenova, T., Zendri, J. -P., Zevin, M., Zhan, M., Zhang, H., Zhang, J., Zhang, L., Zhang, R., Zhang, T., Zhang, Y., Zhao, C., Zhao, G., Zhao, Y., Zhao, Yue, Zhou, R., Zhou, Z., Zhu, X. J., Zhu, Z. -H., Zucker, M. E., Zweizig, J., Antonopoulou, D., Arzoumanian, Z., Basu, A., Bogdanov, S., Cognard, I., Crowter, K., Enoto, T., Flynn, C. M. L., Good, D. C., Guillemot, L., Guillot, S., Harding, A. K., Keith, M. J., Kuiper, L., Lower, M. E., Lyne, A. G., McKee, J. W., Meyers, B. W., Palfreyman, J. L., Shannon, R. M., Shaw, B., Stairs, I. H., Stappers, B. W., Tan, C. M., Theureau, G., and Weltevrede, P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: We present a targeted search for continuous gravitational waves (GWs) from 236 pulsars using data from the third observing run of LIGO and Virgo (O3) combined with data from the second observing run (O2). Searches were for emission from the $l=m=2$ mass quadrupole mode with a frequency at only twice the pulsar rotation frequency (single harmonic) and the $l=2, m=1,2$ modes with a frequency of both once and twice the rotation frequency (dual harmonic). No evidence of GWs was found so we present 95\% credible upper limits on the strain amplitudes $h_0$ for the single harmonic search along with limits on the pulsars' mass quadrupole moments $Q_{22}$ and ellipticities $\varepsilon$. Of the pulsars studied, 23 have strain amplitudes that are lower than the limits calculated from their electromagnetically measured spin-down rates. These pulsars include the millisecond pulsars J0437\textminus4715 and J0711\textminus6830 which have spin-down ratios of 0.87 and 0.57 respectively. For nine pulsars, their spin-down limits have been surpassed for the first time. For the Crab and Vela pulsars our limits are factors of $\sim 100$ and $\sim 20$ more constraining than their spin-down limits, respectively. For the dual harmonic searches, new limits are placed on the strain amplitudes $C_{21}$ and $C_{22}$. For 23 pulsars we also present limits on the emission amplitude assuming dipole radiation as predicted by Brans-Dicke theory., Comment: 37 pages
Published: 2021
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18. A Local Universe Host for the Repeating Fast Radio Burst FRB 20181030A

Author: Bhardwaj, M., Kirichenko, A. Yu., Michilli, D., Mayya, Y. D., Kaspi, V. M., Gaensler, B. M., Rahman, M., Tendulkar, S. P., Fonseca, E., Josephy, Alexander, Leung, C., Merryfield, Marcus, Petroff, Emily, Pleunis, Z., Sanghavi, Pranav, Scholz, P., Shin, K., Smith, Kendrick M., and Stairs, I. H.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We report on the host association of FRB 20181030A, a repeating fast radio burst (FRB) with a low dispersion measure (DM, 103.5 pc cm$^{-3}$) discovered by CHIME/FRB Collaboration et al. (2019a). Using baseband voltage data saved for its repeat bursts, we localize the FRB to a sky area of 5.3 sq. arcmin (90% confidence). Within the FRB localization region, we identify NGC 3252 as the most promising host, with an estimated chance coincidence probability $< 2.5 \times 10^{-3}$. Moreover, we do not find any other galaxy with M$_{r} < -15$ AB mag within the localization region to the maximum estimated FRB redshift of 0.05. This rules out a dwarf host 5 times less luminous than any FRB host discovered to date. NGC 3252 is a star-forming spiral galaxy, and at a distance of $\approx$ 20 Mpc, it is one of the closest FRB hosts discovered thus far. From our archival radio data search, we estimate a 3$\sigma$ upper limit on the luminosity of a persistent compact radio source (source size $<$ 0.3 kpc at 20 Mpc) at 3 GHz to be ${\rm 2 \times 10^{26} erg~s^{-1} Hz^{-1}}$, at least 1500 times smaller than that of the FRB 20121102A persistent radio source. We also argue that a population of young millisecond magnetars alone cannot explain the observed volumetric rate of repeating FRBs. Finally, FRB 20181030A is a promising source for constraining FRB emission models due to its proximity, and we strongly encourage its multi-wavelength follow-up., Comment: Accepted for publication in ApJL
Published: 2021
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19. Study of 72 pulsars discovered in the PALFA survey: Timing analysis, glitch activity, emission variability, and a pulsar in an eccentric binary

Author: Parent, E., Sewalls, H., Freire, P. C. C., Matheny, T., Lyne, A. G., Perera, B. B. P., Cardoso, F., McLaughlin, M. A., Allen, B., Brazier, A., Camilo, F., Chatterjee, S., Cordes, J. M., Crawford, F., Deneva, J. S., Dong, F. A., Ferdman, R. D., Fonseca, E., Hessels, J. W. T., Kaspi, V. M., Knispel, B., van Leeuwen, J., Lynch, R. S., Meyers, B. M., McKee, J. W., Mickaliger, M. B., Patel, C., Ransom, S. M., Rochon, A., Scholz, P., Stairs, I. H., Stappers, B. W., Tan, C. M., and Zhu, W. W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We present new discoveries and results from long-term timing of 72 pulsars discovered in the Arecibo PALFA survey, including precise determination of astrometric and spin parameters, and flux density and scatter broadening measurements at 1.4 GHz. Notable discoveries include two young pulsars (characteristic ages $\sim$30 kyr) with no apparent supernova remnant associations, three mode changing, 12 nulling and two intermittent pulsars. We detected eight glitches in five pulsars. Among them is PSR J1939+2609, an apparently old pulsar (characteristic age $\sim$1 Gy), and PSR J1954+2529, which likely belongs to a newly-emerging class of binary pulsars. The latter is the only pulsar among the 72 that is clearly not isolated: a non-recycled neutron star with a 931-ms spin period in an eccentric ($e\,=\,0.114$) wide ($P_b\,=\,82.7\,$d) orbit with a companion of undetermined nature having a minimum mass of $\sim0.6\,M_{\odot}$. Since operations at Arecibo ceased in 2020 August, we give a final tally of PALFA sky coverage, and compare its 207 pulsar discoveries to the known population. On average, they are 50% more distant than other Galactic plane radio pulsars; PALFA millisecond pulsars (MSP) have twice the dispersion measure per unit spin period than the known population of MSP in the Plane. The four intermittent pulsars discovered by PALFA more than double the population of such objects, which should help to improve our understanding of pulsar magnetosphere physics. The statistics for these, RRATS, and nulling pulsars suggest that there are many more of these objects in the Galaxy than was previously thought., Comment: 39 pages, 18 figures, 9 tables. Accepted for publication in ApJ
Published: 2021
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20. No Evidence for Galactic Latitude Dependence of the Fast Radio Burst Sky Distribution

Author: Josephy, A., Chawla, P., Curtin, A. P., Kaspi, V. M., Bhardwaj, M., Boyle, P. J., Brar, C., Cassanelli, T., Fonseca, E., Gaensler, B. M., Leung, C., Lin, H. -H., Masui, K. W., McKinven, R., Mena-Parra, J., Michilli, D., Ng, C., Pleunis, Z., Rafiei-Ravandi, M., Rahman, M., Sanghavi, P., Scholz, P., Smith, K. M., Stairs, I. H., Tendulkar, S. P., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: We investigate whether the sky rate of Fast Radio Bursts depends on Galactic latitude using the first catalog of Fast Radio Bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project. We first select CHIME/FRB events above a specified sensitivity threshold in consideration of the radiometer equation, and then compare these detections with the expected cumulative time-weighted exposure using Anderson-Darling and Kolmogrov-Smirnov tests. These tests are consistent with the null hypothesis that FRBs are distributed without Galactic latitude dependence ($p$-values distributed from 0.05 to 0.99, depending on completeness threshold). Additionally, we compare rates in intermediate latitudes ($|b| < 15^\circ$) with high latitudes using a Bayesian framework, treating the question as a biased coin-flipping experiment -- again for a range of completeness thresholds. In these tests the isotropic model is significantly favored (Bayes factors ranging from 3.3 to 14.2). Our results are consistent with FRBs originating from an isotropic population of extragalactic sources., Comment: Accepted for publication in ApJ
Published: 2021
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21. Burst timescales and luminosities link young pulsars and fast radio bursts

Author: Nimmo, K., Hessels, J. W. T., Kirsten, F., Keimpema, A., Cordes, J. M., Snelders, M. P., Hewitt, D. M., Karuppusamy, R., Archibald, A. M., Bezukovs, V., Bhardwaj, M., Blaauw, R., Buttaccio, S. T., Cassanelli, T., Conway, J. E., Corongiu, A., Feiler, R., Fonseca, E., Forssen, O., Gawronski, M., Giroletti, M., Kharinov, M. A., Leung, C., Lindqvist, M., Maccaferri, G., Marcote, B., Masui, K. W., Mckinven, R., Melnikov, A., Michilli, D., Mikhailov, A., Ng, C., Orbidans, A., Ould-Boukattine, O. S., Paragi, Z., Pearlman, A. B., Petroff, E., Rahman, M., Scholz, P., Shin, K., Smith, K. M., Stairs, I. H., Surcis, G., Tendulkar, S. P., Vlemmings, W., Wang, N., Yang, J., and Yuan, J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Fast radio bursts (FRBs) are extragalactic radio flashes of unknown physical origin. Their high luminosities and short durations require extreme energy densities, like those found in the vicinity of neutron stars and black holes. Studying the burst intensities and polarimetric properties on a wide range of timescales, from milliseconds down to nanoseconds, is key to understanding the emission mechanism. However, high-time-resolution studies of FRBs are limited by their unpredictable activity levels, available instrumentation and temporal broadening in the intervening ionised medium. Here we show that the repeating FRB 20200120E can produce isolated shots of emission as short as about 60 nanoseconds in duration, with brightness temperatures as high as $3\times 10^{41}$ K (excluding relativistic effects), comparable to `nano-shots' from the Crab pulsar. Comparing both the range of timescales and luminosities, we find that FRB 20200120E observationally bridges the gap between known Galactic young pulsars and magnetars, and the much more distant extragalactic FRBs. This suggests a common magnetically powered emission mechanism spanning many orders of magnitude in timescale and luminosity. In this work, we probe a relatively unexplored region of the short-duration transient phase space; we highlight that there likely exists a population of ultra-fast radio transients at nanosecond to microsecond timescales, which current FRB searches are insensitive to., Comment: Submitted. Comments welcome
Published: 2021

22. A repeating fast radio burst source in a globular cluster

Author: Kirsten, F., Marcote, B., Nimmo, K., Hessels, J. W. T., Bhardwaj, M., Tendulkar, S. P., Keimpema, A., Yang, J., Snelders, M. P., Scholz, P., Pearlman, A. B., Law, C. J., Peters, W. M., Giroletti, M., Paragi, Z., Bassa, C., Hewitt, D. M., Bach, U., Bezrukovs, V., Burgay, M., Buttaccio, S. T., Conway, J. E., Corongiu, A., Feiler, R., Forssén, O., Gawroński, M. P., Karuppusamy, R., Kharinov, M. A., Lindqvist, M., Maccaferri, G., Melnikov, A., Ould-Boukattine, O. S., Possenti, A., Surcis, G., Wang, N., Yuan, J., Aggarwal, K., Anna-Thomas, R., Bower, G. C., Blaauw, R., Burke-Spolaor, S., Cassanelli, T., Clarke, T. E., Fonseca, E., Gaensler, B. M., Gopinath, A., Kaspi, V. M., Kassim, N., Lazio, T. J. W., Leung, C., Li, D. Z., Lin, H. H., Masui, K. W., Mckinven, R., Michilli, D., Mikhailov, A., Ng, C., Orbidans, A., Pen, U. L., Petroff, E., Rahman, M., Ransom, S. M., Shin, K., Smith, K. M., Stairs, I. H., and Vlemmings, W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Fast radio bursts (FRBs) are exceptionally luminous flashes of unknown physical origin, reaching us from other galaxies (Petroff et al. 2019). Most FRBs have only ever been seen once, while others flash repeatedly, though sporadically (Spitler et al. 2016, CHIME/FRB Collaboration et al. 2021). Many models invoke magnetically powered neutron stars (magnetars) as the engines producing FRB emission (Margalit & Metzger 2018, CHIME/FRB Collaboration et al. 2020). Recently, CHIME/FRB announced the discovery (Bhardwaj et al. 2021) of the repeating FRB 20200120E, coming from the direction of the nearby grand design spiral galaxy M81. Four potential counterparts at other observing wavelengths were identified (Bhardwaj et al. 2021) but no definitive association with these sources, or M81, could be made. Here we report an extremely precise localisation of FRB 20200120E, which allows us to associate it with a globular cluster (GC) in the M81 galactic system and to place it ~2pc offset from the optical center of light of the GC. This confirms (Bhardwaj et al. 2021) that FRB 20200120E is 40 times closer than any other known extragalactic FRB. Because such GCs host old stellar populations, this association strongly challenges FRB models that invoke young magnetars formed in a core-collapse supernova as powering FRB emission. We propose, instead, that FRB 20200120E is a highly magnetised neutron star formed via either accretion-induced collapse of a white dwarf or via merger of compact stars in a binary system (Margalit et al. 2019). Alternative scenarios involving compact binary systems, efficiently formed inside globular clusters, could also be responsible for the observed bursts., Comment: Submitted. Comments welcome
Published: 2021
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23. A nearby repeating fast radio burst in the direction of M81

Author: Bhardwaj, M., Gaensler, B. M., Kaspi, V. M., Landecker, T. L., Mckinven, R., Michilli, D., Pleunis, Z., Tendulkar, S. P., Andersen, B. C., Boyle, P. J., Cassanelli, T., Chawla, P., Cook, A., Dobbs, M., Fonseca, E., Kaczmarek, J., Leung, C., Masui, K., Münchmeyer, M., Ng, C., Rafiei-Ravandi, M., Scholz, P., Shin, K., Smith, K. M., Stairs, I. H., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: We report on the discovery of FRB 20200120E, a repeating fast radio burst (FRB) with low dispersion measure (DM), detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB project. The source DM of 87.82 pc cm$^{-3}$ is the lowest recorded from an FRB to date, yet is significantly higher than the maximum expected from the Milky Way interstellar medium in this direction (~ 50 pc cm$^{-3}$). We have detected three bursts and one candidate burst from the source over the period 2020 January-November. The baseband voltage data for the event on 2020 January 20 enabled a sky localization of the source to within $\simeq$ 14 sq. arcmin (90% confidence). The FRB localization is close to M81, a spiral galaxy at a distance of 3.6 Mpc. The FRB appears on the outskirts of M81 (projected offset $\sim$ 20 kpc) but well inside its extended HI and thick disks. We empirically estimate the probability of chance coincidence with M81 to be $< 10^{-2}$. However, we cannot reject a Milky Way halo origin for the FRB. Within the FRB localization region, we find several interesting cataloged M81 sources and a radio point source detected in the Very Large Array Sky Survey (VLASS). We searched for prompt X-ray counterparts in Swift/BAT and Fermi/GBM data, and for two of the FRB 20200120E bursts, we rule out coincident SGR 1806$-$20-like X-ray bursts. Due to the proximity of FRB 20200120E, future follow-up for prompt multi-wavelength counterparts and sub-arcsecond localization could be constraining of proposed FRB models., Comment: Published to ApJL
Published: 2021
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24. The Relativistic Binary Programme on MeerKAT: Science objectives and first results

Author: Kramer, M., Stairs, I. H., Krishnan, V. Venkatraman, Freire, P. C. C., Abbate, F., Bailes, M., Burgay, M., Buchner, S., Champion, D. J., Cognard, I., Gautam, T., Geyer, M., Guillemot, L., Hu, H., Janssen, G., Lower, M. E., Parthasarathy, A., Possenti, A., Ransom, S., Reardon, D. J., Ridolfi, A., Serylak, M., Shannon, R. M., Spiewak, R., Theureau, G., van Straten, W., Wex, N., Oswald, L. S., Posselt, B., Sobey, C., Barr, E. D., Camilo, F., Hugo, B., Jameson, A., Johnston, S., Karastergiou, A., Keith, M., and Oslowski, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: We describe the ongoing Relativistic Binary programme (RelBin), a part of the MeerTime large survey project with the MeerKAT radio telescope. RelBin is primarily focused on observations of relativistic effects in binary pulsars to enable measurements of neutron star masses and tests of theories of gravity. We selected 25 pulsars as an initial high priority list of targets based on their characteristics and observational history with other telescopes. In this paper, we provide an outline of the programme, present polarisation calibrated pulse profiles for all selected pulsars as a reference catalogue along with updated dispersion measures. We report Faraday rotation measures for 24 pulsars, twelve of which have been measured for the first time. More than a third of our selected pulsars show a flat position angle swing confirming earlier observations. We demonstrate the ability of the Rotating Vector Model (RVM), fitted here to seven binary pulsars, including the Double Pulsar (PSR J0737$-$3039A), to obtain information about the orbital inclination angle. We present a high time resolution light curve of the eclipse of PSR J0737$-$3039A by the companion's magnetosphere, a high-phase resolution position angle swing for PSR J1141$-$6545, an improved detection of the Shapiro delay of PSR J1811$-$2405, and pulse scattering measurements for PSRs J1227$-$6208, J1757$-$1854, and J1811$-$1736. Finally, we demonstrate that timing observations with MeerKAT improve on existing data sets by a factor of, typically, 2-3, sometimes by an order of magnitude., Comment: 21 pages 16 figures, published in MNRAS (replaced earlier submission after small changes added in proofs)
Published: 2021
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25. LOFAR Detection of 110-188 MHz Emission and Frequency-Dependent Activity from FRB 20180916B

Author: Pleunis, Z., Michilli, D., Bassa, C. G., Hessels, J. W. T., Naidu, A., Andersen, B. C., Chawla, P., Fonseca, E., Gopinath, A., Kaspi, V. M., Kondratiev, V. I., Li, D. Z., Bhardwaj, M., Boyle, P. J., Brar, C., Cassanelli, T., Gupta, Y., Josephy, A., Karuppusamy, R., Keimpema, A., Kirsten, F., Leung, C., Marcote, B., Masui, K., Mckinven, R., Meyers, B. W., Ng, C., Nimmo, K., Paragi, Z., Rahman, M., Scholz, P., Shin, K., Smith, K. M., Stairs, I. H., and Tendulkar, S. P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: FRB 20180916B is a well-studied repeating fast radio burst source. Its proximity (~150 Mpc), along with detailed studies of the bursts, have revealed many clues about its nature -- including a 16.3-day periodicity in its activity. Here we report on the detection of 18 bursts using LOFAR at 110-188 MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are seen down to the lowest-observed frequency of 110 MHz, suggesting that their spectra extend even lower. These observations provide an order-of-magnitude stronger constraint on the optical depth due to free-free absorption in the source's local environment. The absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300-1700 MHz. Compared with higher frequencies, the larger burst widths (~40-160 ms at 150 MHz) and lower linear polarization fractions are likely due to scattering. We find ~2-3 rad/m^2 variations in the Faraday rotation measure that may be correlated with the activity cycle of the source. We compare the LOFAR burst arrival times to those of 38 previously published and 22 newly detected bursts from the uGMRT (200-450 MHz) and CHIME/FRB (400-800 MHz). Simultaneous observations show 5 CHIME/FRB bursts when no emission is detected by LOFAR. We find that the burst activity is systematically delayed towards lower frequencies by ~3 days from 600 MHz to 150 MHz. We discuss these results in the context of a model in which FRB 20180916B is an interacting binary system featuring a neutron star and high-mass stellar companion., Comment: Accepted for publication by ApJL
Published: 2020
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26. First discovery of new pulsars and RRATs with CHIME/FRB

Author: Good, D. C., Andersen, B. C., Chawla, P., Crowter, K., Dong, F. Q., Fonseca, E., Meyers, B. W., Ng, C., Pleunis, Z., Ransom, S. M., Stairs, I. H., Tan, C. M., Bhardwaj, M., Boyle, P. J., Dobbs, M., Gaensler, B. M., Kaspi, V. M., Masui, K. W., Naidu, A., Rafiei-Ravandi, M., Scholz, P., Smith, K. M., and Tendulkar, S. P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report the discovery of seven new Galactic pulsars with the Canadian Hydrogen Intensity Mapping Experiment's Fast Radio Burst backend (CHIME/FRB). These sources were first identified via single pulses in CHIME/FRB, then followed up with CHIME/Pulsar. Four sources appear to be rotating radio transients (RRATs), pulsar-like sources with occasional single pulse emission with an underlying periodicity. Of those four sources, three have detected periods ranging from 220 ms to 2.726 s. Three sources have more persistent but still intermittent emission and are likely intermittent or nulling pulsars. We have determined phase-coherent timing solutions for the latter three. These seven sources are the first discovery of previously unknown Galactic sources with CHIME/FRB and highlight the potential of fast radio burst detection instruments to search for intermittent Galactic radio sources., Comment: 18 pages, 6 figures, 5 tables, Published by ApJ
Published: 2020
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27. Understanding and improving the timing of PSR J0737-3039B

Author: Noutsos, Aristeidis, Desvignes, G., Kramer, M., Wex, N., Freire, P. C. C., Stairs, I. H., McLaughlin, M. A., Manchester, R. N., Possenti, A., Burgay, M., Lyne, A. G., Breton, R. P., Perera, B. B. P., and Ferdman, R. D.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The double pulsar (PSR J0737-3039A/B) provides some of the most stringent tests of general relativity (GR) and its alternatives. The success of this system in tests of GR is largely due to the high-precision, long-term timing of its recycled-pulsar member, pulsar A. On the other hand, pulsar B is a young pulsar that exhibits significant short-term and long-term timing variations due to the electromagnetic-wind interaction with its companion and geodetic precession. Improving pulsar B's timing precision is a key step towards improving the precision in a number of GR tests with PSR J0737-3039A/B. In this paper, red noise signatures in the timing of pulsar B are investigated using roughly a four-year time span, from 2004 to 2008, beyond which time the pulsar's radio beam precessed out of view ... The timing of pulsar B presented in this paper depends on the size of the pulsar's orbit, which was calculated from GR, in order to precisely account for orbital timing delays. Consequently, our timing cannot directly be used to test theories of gravity. However, our modelling of the beam shape and radial wind of pulsar B can indirectly aid future efforts to time this pulsar by constraining part of the additional red noise observed on top of the orbital delays. As such, we conclude that, in the idealised case of zero covariance between our model's parameters and those of the timing model, our model can bring about a factor 2.6 improvement on the measurement precision of the mass ratio, R = mA/mB, between the two pulsars: a theory-independent parameter, which is pivotal in tests of GR., Comment: 43 pages, 28 figures, Accepted in A&A
Published: 2020
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28. An analysis pipeline for CHIME/FRB full-array baseband data

Author: Michilli, D., Masui, K. W., Mckinven, R., Cubranic, D., Bruneault, M., Brar, C., Patel, C., Boyle, P. J., Stairs, I. H., Renard, A., Bandura, K., Berger, S., Breitman, D., Cassanelli, T., Dobbs, M., Kaspi, V. M., Leung, C., Mena-Parra, J., Pleunis, Z., Russell, L., Scholz, P., Siegel, S. R., Tendulkar, S. P., and Vanderlinde, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has become a leading facility for detecting fast radio bursts (FRBs) through the CHIME/FRB backend. CHIME/FRB searches for fast transients in polarization-summed intensity data streams that have 24-kHz spectral and 1-ms temporal resolution. The intensity beams are pointed to pre-determined locations in the sky. A triggered baseband system records the coherent electric field measured by each antenna in the CHIME array at the time of FRB detections. Here we describe the analysis techniques and automated pipeline developed to process these full-array baseband data recordings. Whereas the real-time FRB detection pipeline has a localization limit of several arcminutes, offline analysis of baseband data yields source localizations with sub-arcminute precision, as characterized by using a sample of pulsars and one repeating FRB with known positions. The baseband pipeline also enables resolving temporal substructure on a micro-second scale and the study of polarization including detections of Faraday rotation.
Published: 2020
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29. The Discovery of Nulling and Mode Switching Pulsars with CHIME/Pulsar

Author: Ng, C., Wu, B., Ma, M., Ransom, S. M., Naidu, A., Fonseca, E., Boyle, P. J., Brar, C., Cubranic, D., Demorest, P. B., Good, D. C., Kaspi, V. M., Masui, K. W., Michilli, D., Patel, C., Renard, A., Scholz, P., Stairs, I. H., Tendulkar, S. P., Tretyakov, I., and Vanderlinde, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Solar and Stellar Astrophysics
Abstract: The Pulsar backend of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has monitored hundreds of known pulsars in the northern sky since Fall 2018, providing a rich data set for the study of temporal variations in pulsar emission. Using a matched filtering technique, we report, for the first time, nulling behaviour in five pulsars as well as mode switching in nine pulsars. Only one of the pulsars is observed to show both nulling and moding signals. These new nulling and mode switching pulsars appear to come from a population with relatively long spin periods, in agreement with previous findings in the literature., Comment: 11 pages, 7 figures, 2 tables, accepted by ApJ
Published: 2020
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30. The CHIME Pulsar Project: System Overview

Author: Collaboration, CHIME/Pulsar, Amiri, M., Bandura, K. M., Boyle, P. J., Brar, C., Cliche, J. F., Crowter, K., Cubranic, D., Demorest, P. B., Denman, N. T., Dobbs, M., Dong, F. Q., Fandino, M., Fonseca, E., Good, D. C., Halpern, M., Hill, A. S., Höfer, C., Kaspi, V. M., Landecker, T. L., Leung, C., Lin, H. -H., Luo, J., Masui, K. W., McKee, J. W., Mena-Parra, J., Meyers, B. W., Michilli, D., Naidu, A., Newburgh, L., Ng, C., Patel, C., Pinsonneault-Marotte, T., Ransom, S. M., Renard, A., Scholz, P., Shaw, J. R., Sikora, A. E., Stairs, I. H., Tan, C. M., Tendulkar, S. P., Tretyakov, I., Vanderlinde, K., Wang, H., and Wang, X.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We present the design, implementation and performance of a digital backend constructed for the Canadian Hydrogen Intensity Mapping Experiment (CHIME) that uses accelerated computing to observe radio pulsars and transient radio sources. When operating, the CHIME correlator outputs 10 independent streams of beamformed data for the CHIME/Pulsar backend that digitally track specified celestial positions. Each of these independent streams are processed by the CHIME/Pulsar backend system which can coherently dedisperse, in real-time, up to dispersion measure values of 2500 pc/cm$^{-3}$ . The tracking beams and real-time analysis system are autonomously controlled by a priority-based algorithm that schedules both known sources and positions of interest for observation with observing cadences as small as one day. Given the distribution of known pulsars and radio-transient sources, the CHIME/Pulsar system can monitor up to 900 positions once per sidereal day and observe all sources with declinations greater than $-20^\circ$ once every $\sim$2 weeks. We also discuss the science program enabled through the current modes of data acquisition for CHIME/Pulsar that centers on timing and searching experiments., Comment: 18 pages, 9 figures, 1 table. Submitted to ApJS
Published: 2020
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31. First Discovery of a Fast Radio Burst at 350 MHz by the GBNCC Survey

Author: Parent, E., Chawla, P., Kaspi, V. M., Agazie, G. Y., Blumer, H., DeCesar, M., Fiore, W., Fonseca, E., Hessels, J. W. T., Kaplan, D. L., Kondratiev, V. I., LaRose, M., Levin, L., Lewis, E. F., Lynch, R. S., McEwen, A. E., McLaughlin, M. A., Mingyar, M., Noori, H. Al, Ransom, S. M., Roberts, M. S. E., Schmiedekamp, A., Schmiedekamp, C., Siemens, X., Spiewak, R., Stairs, I. H., Surnis, M., Swiggum, J., and van Leeuwen, J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report the first discovery of a fast radio burst (FRB), FRB 20200125A, by the Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey conducted with the Green Bank Telescope at 350 MHz. FRB 20200125A was detected at a Galactic latitude of 58.43 degrees with a dispersion measure of 179 pc cm$^{-3}$, while electron density models predict a maximum Galactic contribution of 25 pc cm$^{-3}$ along this line of sight. Moreover, no apparent Galactic foreground sources of ionized gas that could account for the excess DM are visible in multi-wavelength surveys of this region. This argues that the source is extragalactic. The maximum redshift for the host galaxy is $z_{max}=0.17$, corresponding to a maximum comoving distance of approximately 750 Mpc. The measured peak flux density for FRB 20200125A is 0.37 Jy, and we measure a pulse width of 3.7 ms, consistent with the distribution of FRB widths observed at higher frequencies. Based on this detection and assuming an Euclidean flux density distribution of FRBs, we calculate an all-sky rate at 350 MHz of $3.4^{+15.4}_{-3.3} \times 10^3$ FRBs sky$^{-1}$ day$^{-1}$ above a peak flux density of 0.42 Jy for an unscattered pulse having an intrinsic width of 5 ms, consistent with rates reported at higher frequencies. Given the recent improvements in our single-pulse search pipeline, we also revisit the GBNCC survey sensitivity to various burst properties. Finally, we find no evidence of interstellar scattering in FRB 20200125A, adding to the growing evidence that some FRBs have circumburst environments where free-free absorption and scattering are not significant., Comment: 15 pages, 6 figures, Submitted to ApJ
Published: 2020
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32. Asymmetric mass ratios for bright double neutron-star mergers

Author: Ferdman, R. D., Freire, P. C. C., Perera, B. B. P., Pol, N., Camilo, F., Chatterjee, S., Cordes, J. M., Crawford, F., Hessels, J. W. T., Kaspi, V. M., McLaughlin, M. A., Parent, E., Stairs, I. H., and van Leeuwen, J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics, General Relativity and Quantum Cosmology
Abstract: The discovery of a radioactively powered kilonova associated with the binary neutron star merger GW170817 was the first - and still only - confirmed electromagnetic counterpart to a gravitational-wave event. However, observations of late-time electromagnetic emission are in tension with the expectations from standard neutron-star merger models. Although the large measured ejecta mass is potentially explained by a progenitor system that is asymmetric in terms of the stellar component masses, i.e. with a mass ratio $q$ of 0.7-0.8, the known Galactic population of merging double neutron star (DNS) systems (i.e. those that will coalesce within billions of years or less) has, until now, only consisted of nearly equal-mass ($q > 0.9$) binaries. PSR J1913+1102 is a DNS system in a 5-hour, low-eccentricity ($e = 0.09$) orbit, implying an orbital separation of 1.8 solar radii, with the two neutron stars predicted to coalesce in 470 million years due to gravitational-wave emission. Here we report that the masses of the two neutron stars, as measured by a dedicated pulsar timing campaign, are $1.62 \pm 0.03$ and $1.27 \pm 0.03$ solar masses for the pulsar and companion neutron star, respectively; with a measured mass ratio $q = 0.78 \pm 0.03$, it is the most asymmetric DNS among known merging systems. Based on this detection, our population synthesis analysis implies that such asymmetric binaries represent between 2 and 30% (90% confidence) of the total population of merging DNS binaries. The coalescence of a member of this population offers a possible explanation for the anomalous properties of GW170817, including the observed kilonova emission from that event., Comment: 17 pages, 3 figures, published in Nature on 9 July 2020 (https://www.nature.com/articles/s41586-020-2439-x); this is the authors' final submitted version before review. Includes methods and supplementary information
Published: 2020
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33. Faraday rotation measures of northern-hemisphere pulsars using CHIME/Pulsar

Author: Ng, C., Pandhi, A., Naidu, A., Fonseca, E., Kaspi, V. M., Masui, K. W., Mckinven, R., Renard, A., Scholz, P., Stairs, I. H., Tendulkar, S. P., and Vanderlinde, K.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: Using commissioning data from the first year of operation of the Canadian Hydrogen Intensity Mapping Experiment's (CHIME) Pulsar backend system, we conduct a systematic analysis of the Faraday Rotation Measure (RM) of the northern hemisphere pulsars detected by CHIME. We present 55 new RMs as well as obtain improved RM uncertainties for 25 further pulsars. CHIME's low observing frequency and wide bandwidth between 400-800 MHz contribute to the precision of our measurements, whereas the high cadence observation provide extremely high signal-to-noise co-added data. Our results represent a significant increase of the pulsar RM census, particularly regarding the northern hemisphere. These new RMs are for sources that are located in the 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., Comment: 13 pages, 7 figures, accepted by MNRAS
Published: 2020
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34. The MeerKAT Telescope as a Pulsar Facility: System verification and early science results from MeerTime

Author: Bailes, M., Jameson, A., Abbate, F., Barr, E. D., Bhat, N. D. R., Bondonneau, L., Burgay, M., Buchner, S. J., Camilo, F., Champion, D. J., Cognard, I., Demorest, P. B., Freire, P. C. C., Gautam, T., Geyer, M., Griessmeier, J. M., Guillemot, L., Hu, H., Jankowski, F., Johnston, S., Karastergiou, A., Karuppusamy, R., Kaur, D., Keith, M. J., Kramer, M., van Leeuwen, J., Lower, M. E., Maan, Y., McLaughlin, M. A., Meyers, B. W., Osłowski, S., Oswald, L. S., Parthasarathy, A., Pennucci, T., Posselt, B., Possenti, A., Ransom, S. M., Reardon, D. J., Ridolfi, A., Schollar, C. T. G., Serylak, M., Shaifullah, G., Shamohammadi, M., Shannon, R. M., Sobey, C., Song, X., Spiewak, R., Stairs, I. H., Stappers, B. W., van Straten, W., Szary, A., Theureau, G., Krishnan, V. Venkatraman, Weltevrede, P., Wex, N., Abbott, T. D., Adams, G. B., Burger, J. P., Gamatham, R. R. G., Gouws, M., Horn, D. M., Hugo, B., Joubert, A. F., Manley, J. R., McAlpine, K., Passmoor, S. S., Peens-Hough, A., Ramudzuli, Z. R., Rust, A., Salie, S., Schwardt, L. C., Siebrits, R., Van Tonder, G., Van Tonder, V., and Welz, M. G.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: We describe system verification tests and early science results from the pulsar processor (PTUSE) developed for the newly-commissioned 64-dish SARAO MeerKAT radio telescope in South Africa. MeerKAT is a high-gain (~2.8 K/Jy) low-system temperature (~18 K at 20cm) radio array that currently operates from 580-1670 MHz and can produce tied-array beams suitable for pulsar observations. This paper presents results from the MeerTime Large Survey Project and commissioning tests with PTUSE. Highlights include observations of the double pulsar J0737-3039A, pulse profiles from 34 millisecond pulsars from a single 2.5h observation of the Globular cluster Terzan 5, the rotation measure of Ter5O, a 420-sigma giant pulse from the Large Magellanic Cloud pulsar PSR J0540-6919, and nulling identified in the slow pulsar PSR J0633-2015. One of the key design specifications for MeerKAT was absolute timing errors of less than 5 ns using their novel precise time system. Our timing of two bright millisecond pulsars confirm that MeerKAT delivers exceptional timing. PSR J2241-5236 exhibits a jitter limit of <4 ns per hour whilst timing of PSR J1909-3744 over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. Our results confirm that the MeerKAT is an exceptional pulsar telescope. The array can be split into four separate sub-arrays to time over 1000 pulsars per day and the future deployment of S-band (1750-3500 MHz) receivers will further enhance its capabilities., Comment: 20 pages, 16 Figures, 4 Tables, accepted for publication in PASA
Published: 2020
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35. A bright millisecond-duration radio burst from a Galactic magnetar

Author: Collaboration, The CHIME/FRB, Andersen, B. C., Bandura, K. M., Bhardwaj, M., Bij, A., Boyce, M. M., Boyle, P. J., Brar, C., Cassanelli, T., Chawla, P., Chen, T., Cliche, J. -F., Cook, A., Cubranic, D., Curtin, A. P., Denman, N. T., Dobbs, M., Dong, F. Q., Fandino, M., Fonseca, E., Gaensler, B. M., Giri, U., Good, D. C., Halpern, M., Hill, A. S., Hinshaw, G. F., Höfer, C., Josephy, A., Kania, J. W., Kaspi, V. M., Landecker, T. L., Leung, C., Li, D. Z., Lin, H. -H., Masui, K. W., Mckinven, R., Mena-Parra, J., Merryfield, M., Meyers, B. W., Michilli, D., Milutinovic, N., Mirhosseini, A., Münchmeyer, M., Naidu, A., Newburgh, L. B., Ng, C., Patel, C., Pen, U. -L., Pinsonneault-Marotte, T., Pleunis, Z., Quine, B. M., Rafiei-Ravandi, M., Rahman, M., Ransom, S. M., Renard, A., Sanghavi, P., Scholz, P., Shaw, J. R., Shin, K., Siegel, S. R., Singh, S., Smegal, R. J., Smith, K. M., Stairs, I. H., Tan, C. M., Tendulkar, S. P., Tretyakov, I., Vanderlinde, K., Wang, H., Wulf, D., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Magnetars are highly magnetized young neutron stars that occasionally produce enormous bursts and flares of X-rays and gamma-rays. Of the approximately thirty magnetars currently known in our Galaxy and Magellanic Clouds, five have exhibited transient radio pulsations. Fast radio bursts (FRBs) are millisecond-duration bursts of radio waves arriving from cosmological distances. Some have been seen to repeat. A leading model for repeating FRBs is that they are extragalactic magnetars, powered by their intense magnetic fields. However, a challenge to this model has been that FRBs must have radio luminosities many orders of magnitude larger than those seen from known Galactic magnetars. Here we report the detection of an extremely intense radio burst from the Galactic magnetar SGR 1935+2154 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project. The fluence of this two-component bright radio burst and the estimated distance to SGR 1935+2154 together imply a 400-800 MHz burst energy of $\sim 3 \times 10^{34}$ erg, which is three orders of magnitude brighter than those of any radio-emitting magnetar detected thus far. Such a burst coming from a nearby galaxy would be indistinguishable from a typical FRB. This event thus bridges a large fraction of the radio energy gap between the population of Galactic magnetars and FRBs, strongly supporting the notion that magnetars are the origin of at least some FRBs., Comment: Submitted to Nature. This version: Geocentric arrival time corrected
Published: 2020
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36. Simultaneous X-ray and Radio Observations of the Repeating Fast Radio Burst FRB 180916.J0158+65

Author: Scholz, P., Cook, A., Cruces, M., Hessels, J. W. T., Kaspi, V. M., Majid, W. A., Naidu, A., Pearlman, A. B., Spitler, L., Bandura, K. M., Bhardwaj, M., Cassanelli, T., Chawla, P., Gaensler, B. M., Good, D. C., Josephy, A., Karuppusamy, R., Keimpema, A., Kirichenko, A. Yu., Kirsten, F., Kocz, J., Leung, C., Marcote, B., Masui, K., Mena-Parra, J., Merryfield, M., Michilli, D., Naudet, C. J., Nimmo, K., Pleunis, Z., Prince, T. A., Rafiei-Ravandi, M., Rahman, M., Shin, K., Smith, K. M., Stairs, I. H., Tendulkar, S. P., and Vanderlinde, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on simultaneous radio and X-ray observations of the repeating fast radio burst source FRB 180916.J0158+65 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Effelsberg, and Deep Space Network (DSS-14 and DSS-63) radio telescopes and the Chandra X-ray Observatory. During 33 ks of Chandra observations, we detect no radio bursts in overlapping Effelsberg or Deep Space Network observations and a single radio burst during CHIME/FRB source transits. We detect no X-ray events in excess of the background during the Chandra observations. These non-detections imply a 5-$\sigma$ limit of $<5\times10^{-10}$ erg cm$^{-2}$ for the 0.5--10 keV fluence of prompt emission at the time of the radio burst and $1.3\times10^{-9}$ erg cm$^{-2}$ at any time during the Chandra observations at the position of FRB 180916.J0158+65. Given the host-galaxy redshift of FRB 180916.J0158+65 ($z\sim0.034$), these correspond to energy limits of $<1.6\times10^{45}$ erg and $<4\times10^{45}$ erg, respectively. We also place a 5-$\sigma$ limit of $<8\times10^{-15}$ erg s$^{-1}$ cm$^{-2}$ on the 0.5--10\,keV absorbed flux of a persistent source at the location of FRB 180916.J0158+65. This corresponds to a luminosity limit of $<2\times10^{40}$ erg s$^{-1}$. Using Fermi/GBM data we search for prompt gamma-ray emission at the time of radio bursts from FRB 180916.J0158+65 and find no significant bursts, placing a limit of $4\times10^{-9}$ erg cm$^{-2}$ on the 10--100 keV fluence. We also search Fermi/LAT data for periodic modulation of the gamma-ray brightness at the 16.35-day period of radio-burst activity and detect no significant modulation. We compare these deep limits to the predictions of various fast radio burst models, but conclude that similar X-ray constraints on a closer fast radio burst source would be needed to strongly constrain theory., Comment: 16 pages, 2 figures, submitted to ApJ
Published: 2020
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37. Detection of Repeating FRB 180916.J0158+65 Down to Frequencies of 300 MHz

Author: Chawla, P., Andersen, B. C., Bhardwaj, M., Fonseca, E., Josephy, A., Kaspi, V. M., Michilli, D., Pleunis, Z., Bandura, K. M., Bassa, C. G., Boyle, P. J., Brar, C., Cassanelli, T., Cubranic, D., Dobbs, M., Dong, F. Q., Gaensler, B. M., Good, D. C., Hessels, J. W. T., Landecker, T. L., Leung, C., Li, D. Z., Lin, H. -. H., Masui, K., Mckinven, R., Mena-Parra, J., Merryfield, M., Meyers, B. W., Naidu, A., Ng, C., Patel, C., Rafiei-Ravandi, M., Rahman, M., Sanghavi, P., Scholz, P., Shin, K., Smith, K. M., Stairs, I. H., Tendulkar, S. P., and Vanderlinde, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on the detection of seven bursts from the periodically active, repeating fast radio burst (FRB) source FRB 180916.J0158+65 in the 300-400-MHz frequency range with the Green Bank Telescope (GBT). Emission in multiple bursts is visible down to the bottom of the GBT band, suggesting that the cutoff frequency (if it exists) for FRB emission is lower than 300 MHz. Observations were conducted during predicted periods of activity of the source, and had simultaneous coverage with the Low Frequency Array (LOFAR) and the FRB backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. We find that one of the GBT-detected bursts has potentially associated emission in the CHIME band (400-800 MHz) but we detect no bursts in the LOFAR band (110-190 MHz), placing a limit of $\alpha > -1.0$ on the spectral index of broadband emission from the source. We also find that emission from the source is severely band-limited with burst bandwidths as low as $\sim$40 MHz. In addition, we place the strictest constraint on observable scattering of the source, $<$ 1.7 ms, at 350 MHz, suggesting that the circumburst environment does not have strong scattering properties. Additionally, knowing that the circumburst environment is optically thin to free-free absorption at 300 MHz, we find evidence against the association of a hyper-compact HII region or a young supernova remnant (age $<$ 50 yr) with the source., Comment: Accepted for publication in ApJL
Published: 2020
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38. Periodic activity from a fast radio burst source

Author: Collaboration, The CHIME/FRB, Amiri, M., Andersen, B. C., Bandura, K. M., Bhardwaj, M., Boyle, P. J., Brar, C., Chawla, P., Chen, T., Cliche, J. F., Cubranic, D., Deng, M., Denman, N. T., Dobbs, M., Dong, F. Q., Fandino, M., Fonseca, E., Gaensler, B. M., Giri, U., Good, D. C., Halpern, M., Hessels, J. W. T., Hill, A. S., Höfer, C., Josephy, A., Kania, J. W., Karuppusamy, R., Kaspi, V. M., Keimpema, A., Kirsten, F., Landecker, T. L., Lang, D. A., Leung, C., Li, D. Z., Lin, H. -H., Marcote, B., Masui, K. W., Mckinven, R., Mena-Parra, J., Merryfield, M., Michilli, D., Milutinovic, N., Mirhosseini, A., Naidu, A., Newburgh, L. B., Ng, C., Nimmo, K., Paragi, Z., Patel, C., Pen, U. -L., Pinsonneault-Marotte, T., Pleunis, Z., Rafiei-Ravandi, M., Rahman, M., Ransom, S. M., Renard, A., Sanghavi, P., Scholz, P., Shaw, J. R., Shin, K., Siegel, S. R., Singh, S., Smegal, R. J., Smith, K. M., Stairs, I. H., Tendulkar, S. P., Tretyakov, I., Vanderlinde, K., Wang, H., Wang, X., Wulf, D., Yadav, P., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Fast radio bursts (FRBs) are bright, millisecond-duration radio transients originating from extragalactic distances. Their origin is unknown. Some FRB sources emit repeat bursts, ruling out cataclysmic origins for those events. Despite searches for periodicity in repeat burst arrival times on time scales from milliseconds to many days, these bursts have hitherto been observed to appear sporadically, and though clustered, without a regular pattern. Here we report the detection of a $16.35\pm0.15$ day periodicity (or possibly a higher-frequency alias of that periodicity) from a repeating FRB 180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project (CHIME/FRB). In 38 bursts recorded from September 16th, 2018 through February 4th, 2020, we find that all bursts arrive in a 5-day phase window, and 50% of the bursts arrive in a 0.6-day phase window. Our results suggest a mechanism for periodic modulation either of the burst emission itself, or through external amplification or absorption, and disfavour models invoking purely sporadic processes.
Published: 2020
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39. Nine New Repeating Fast Radio Burst Sources from CHIME/FRB

Author: Fonseca, E., Andersen, B. C., Bhardwaj, M., Chawla, P., Good, D. C., Josephy, A., Kaspi, V. M., Masui, K. W., Mckinven, R., Michilli, D., Pleunis, Z., Shin, K., Tendulkar, S. P., Bandura, K. M., Boyle, P. J., Brar, C., Cassanelli, T., Cubranic, D., Dobbs, M., Dong, F. Q., Gaensler, B. M., Hinshaw, G., Landecker, T. L., Leung, C., Li, D. Z., Lin, H. -H., Mena-Parra, J., Merryfield, M., Naidu, A., Ng, C., Patel, C., Pen, U., Rafiei-Ravandi, M., Rahman, M., Ransom, S. M., Scholz, P., Smith, K. M., Stairs, I. H., Vanderlinde, K., Yadav, P., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on the discovery and analysis of bursts from nine new repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources span a dispersion measure (DM) range of 195 to 1380 pc cm$^{-3}$. We detect two bursts from three of the new sources, three bursts from four of the new sources, four bursts from one new source, and five bursts from one new source. We determine sky coordinates of all sources with uncertainties of $\sim$10$^\prime$. We detect Faraday rotation measures for two sources, with values $-20(1)$ and $-499.8(7)$ rad m$^{-2}$, that are substantially lower than the RM derived from bursts emitted by FRB 121102. We find that the DM distribution of our events, combined with the nine other repeaters discovered by CHIME/FRB, is indistinguishable from that of thus far non-repeating CHIME/FRB events. However, as previously reported, the burst widths appear statistically significantly larger than the thus far non-repeating CHIME/FRB events, further supporting the notion of inherently different emission mechanisms and/or local environments. These results are consistent with previous work, though are now derived from 18 repeating sources discovered by CHIME/FRB during its first year of operation. We identify candidate galaxies that may contain FRB 190303.J1353+48 (DM = 222.4 pc cm$^{-3}$)., Comment: Accepted for publication in ApJL
Published: 2020
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40. A repeating fast radio burst source localised to a nearby spiral galaxy

Author: Marcote, B., Nimmo, K., Hessels, J. W. T., Tendulkar, S. P., Bassa, C. G., Paragi, Z., Keimpema, A., Bhardwaj, M., Karuppusamy, R., Kaspi, V. M., Law, C. J., Michilli, D., Aggarwal, K., Andersen, B., Archibald, A. M., Bandura, K., Bower, G. C., Boyle, P. J., Brar, C., Burke-Spolaor, S., Butler, B. J., Cassanelli, T., Chawla, P., Demorest, P., Dobbs, M., Fonseca, E., Giri, U., Good, D. C., Gourdji, K., Josephy, A., Kirichenko, A. Yu., Kirsten, F., Landecker, T. L., Lang, D., Lazio, T. J. W., Li, D. Z., Lin, H. -H., Linford, J. D., Masui, K., Mena-Parra, J., Naidu, A., Ng, C., Patel, C., Pen, U. -L., Pleunis, Z., Rafiei-Ravandi, M., Rahman, M., Renard, A., Scholz, P., Siegel, S. R., Smith, K. M., Stairs, I. H., Vanderlinde, K., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: Fast radio bursts (FRBs) are brief, bright, extragalactic radio flashes. Their physical origin remains unknown, but dozens of possible models have been postulated. Some FRB sources exhibit repeat bursts. Though over a hundred FRB sources have been discovered to date, only four have been localised and associated with a host galaxy, with just one of the four known to repeat. The properties of the host galaxies, and the local environments of FRBs, provide important clues about their physical origins. However, the first known repeating FRB has been localised to a low-metallicity, irregular dwarf galaxy, and the apparently non-repeating sources to higher-metallicity, massive elliptical or star-forming galaxies, suggesting that perhaps the repeating and apparently non-repeating sources could have distinct physical origins. Here we report the precise localisation of a second repeating FRB source, FRB 180916.J0158+65, to a star-forming region in a nearby (redshift $z = 0.0337 \pm 0.0002$) massive spiral galaxy, whose properties and proximity distinguish it from all known hosts. The lack of both a comparably luminous persistent radio counterpart and a high Faraday rotation measure further distinguish the local environment of FRB 180916.J0158+65 from that of the one previously localised repeating FRB source, FRB 121102. This demonstrates that repeating FRBs have a wide range of luminosities, and originate from diverse host galaxies and local environments., Comment: 61 pages, 11 figures, 3 tables. Published in Nature
Published: 2020
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41. Modeling the uncertainties of solar-system ephemerides for robust gravitational-wave searches with pulsar timing arrays

Author: Vallisneri, M., Taylor, S. R., Simon, J., Folkner, W. M., Park, R. S., Cutler, C., Ellis, J. A., Lazio, T. J. W., Vigeland, S. J., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., van Haasteren, R., Witt, C. A., and Zhu, W. W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology
Abstract: The regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of Earth's position with respect to the solar-system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar timing arrays. Indeed, recent array datasets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar-system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article we describe the motivation, construction, and application of a physical model of solar-system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGrav's 11-yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11-yr dataset; and that this degeneracy will vanish with improved ephemerides and with the longer pulsar timing datasets that will become available in the near future., Comment: Fixed typo in author list. Code that supports all calculations and figures is available at github.com/nanograv/11yr_stochastic_analysis/tree/master/bayesephem
Published: 2020
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42. The NANOGrav 11-year Data Set: Constraints on Planetary Masses Around 45 Millisecond Pulsars

Author: Behrens, E. A., Ransom, S. M., Madison, D. R., Arzoumanian, Z., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Perera, B. B. P., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., and Zhu, W. W.
Subjects: Astrophysics - Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: We search for extrasolar planets around millisecond pulsars using pulsar timing data and seek to determine the minimum detectable planetary masses as a function of orbital period. Using the 11-year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), we look for variations from our models of pulse arrival times due to the presence of exoplanets. No planets are detected around the millisecond pulsars in the NANOGrav 11-year data set, but taking into consideration the noise levels of each pulsar and the sampling rate of our observations, we develop limits that show we are sensitive to planetary masses as low as that of the moon. We analyzed potential planet periods, P, in the range 7 days < P < 2000 days, with somewhat smaller ranges for some binary pulsars. The planetary mass limit for our median-sensitivity pulsar within this period range is 1 M_moon (P / 100 days)^(-2/3)., Comment: Revised and accepted by ApJ Letters
Published: 2019
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43. The NANOGrav 11-Year Data Set: Limits on Gravitational Wave Memory

Author: Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Decesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Vallisneri, M., Van Haasterer, R., Vigeland, S. J., Witt, C. A., and Zhu, W. W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: The mergers of supermassive black hole binaries (SMBHBs) promise to be incredible sources of gravitational waves (GWs). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays (PTAs), the non-oscillatory GW memory effect is detectable. Further, any burst of gravitational waves will produce GW memory, making memory a useful probe of unmodeled exotic sources and new physics. We searched the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GW memory. This dataset is sensitive to very low frequency GWs of $\sim3$ to $400$ nHz (periods of $\sim11$ yr $-$ $1$ mon). Finding no evidence for GWs, we placed limits on the strain amplitude of GW memory events during the observation period. We then used the strain upper limits to place limits on the rate of GW memory causing events. At a strain of $2.5\times10^{-14}$, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of GW memory events at $<0.4$ yr$^{-1}$. That strain corresponds to a SMBHB merger with reduced mass of $\eta M \sim 2\times10^{10}M_\odot$ and inclination of $\iota=\pi/3$ at a distance of 1 Gpc. As a test of our analysis, we analyzed the NANOGrav 9-year data set as well. This analysis found an anomolous signal, which does not appear in the 11-year data set. This signal is not a GW, and its origin remains unknown., Comment: 10 pages, 6 figures, submitted to ApJ
Published: 2019
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44. A pulsar-based timescale from the International Pulsar Timing Array

Author: Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Oslowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., and Zhu, X. J.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We have constructed a new timescale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar timescale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected timescale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based timescales are unlikely to contribute to the stability of the best timescales over the next decade, but they will remain a valuable independent check on atomic timescales. We also find that the stability of the pulsar-based timescale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves., Comment: accepted by MNRAS
Published: 2019
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45. Revealing the Origin and Cosmic Evolution of Supermassive Black Holes

Author: Woods, T. E., Alexandroff, R. M., Ellison, S. L., Ferrarese, L., Gallagher, S. C., Gallo, L., Haggard, D., Hall, P. B., Hlavacek-Larrondo, J., Khatu, V. C., Man, A. W. S., McGee, S., McNamara, B. R., Ruan, J., Sivakoff, G., Stairs, I. H., and Willott, C.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: The next generation of electromagnetic and gravitational wave observatories will open unprecedented windows to the birth of the first supermassive black holes. This has the potential to reveal their origin and growth in the first billion years, as well as the signatures of their formation history in the local Universe. With this in mind, we outline three key focus areas which will shape research in the next decade and beyond: (1) What were the "seeds" of the first quasars; how did some reach a billion solar masses before z$\sim7$? (2) How does black hole growth change over cosmic time, and how did the early growth of black holes shape their host galaxies? What can we learn from intermediate mass black holes (IMBHs) and dwarf galaxies today? (3) Can we unravel the physics of black hole accretion, understanding both inflows and outflows (jets and winds) in the context of the theory of general relativity? Is it valid to use these insights to scale between stellar and supermassive BHs, i.e., is black hole accretion really scale invariant? In the following, we identify opportunities for the Canadian astronomical community to play a leading role in addressing these issues, in particular by leveraging our strong involvement in the Event Horizon Telescope, the {\it James Webb Space Telescope} (JWST), Euclid, the Maunakea Spectroscopic Explorer (MSE), the Thirty Meter Telescope (TMT), the Square Kilometer Array (SKA), the Cosmological Advanced Survey Telescope for Optical and ultraviolet Research (CASTOR), and more. We also discuss synergies with future space-based gravitational wave (LISA) and X-ray (e.g., Athena, Lynx) observatories, as well as the necessity for collaboration with the stellar and galactic evolution communities to build a complete picture of the birth of supermassive black holes, and their growth and their influence over the history of the Universe., Comment: White paper submitted to Canadian 2020 Long Range Plan committee. 11 pages, 3 figures
Published: 2019
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46. The NANOGrav 11-Year Data Set: Evolution of Gravitational Wave Background Statistics

Author: Hazboun, J. S., Simon, J., Taylor, S. R., Lam, M. T., Vigeland, S. J., Islo, K., Key, J. S., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Holgado, A. M., Huerta, E. A., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Turner, J. E., Vallisneri, M., van Haasteren, R., Witt, C. A., and Zhu, W. W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology
Abstract: An ensemble of inspiraling supermassive black hole binaries should produce a stochastic background of very low frequency gravitational waves. This stochastic background is predicted to be a power law, with a spectral index of -2/3, and it should be detectable by a network of precisely timed millisecond pulsars, widely distributed on the sky. This paper reports a new "time slicing" analysis of the 11-year data release from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) using 34 millisecond pulsars. Methods to flag potential "false positive" signatures are developed, including techniques to identify responsible pulsars. Mitigation strategies are then presented. We demonstrate how an incorrect noise model can lead to spurious signals, and show how independently modeling noise across 30 Fourier components, spanning NANOGrav's frequency range, effectively diagnoses and absorbs the excess power in gravitational-wave searches. This results in a nominal, and expected, progression of our gravitational-wave statistics. Additionally we show that the first interstellar medium event in PSR J1713+0747 pollutes the common red noise process with low-spectral index noise, and use a tailored noise model to remove these effects., Comment: 14 pages, 13 figures, fixed typo in abstract of earlier version
Published: 2019
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47. The International Pulsar Timing Array: Second data release

Author: Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Oslowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., and Zhu, X. J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science., Comment: Submitted to MNRAS and in review, 23 pages, 5 figures
Published: 2019
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48. Eight Millisecond Pulsars Discovered in the Arecibo PALFA Survey

Author: Parent, E., Kaspi, V. M., Ransom, S. M., Freire, P. C. C., Brazier, A., Camilo, F., Chatterjee, S., Cordes, J. M., Crawford, F., Deneva, J. S., Ferdman, R. D., Hessels, J. W. T., van Leeuwen, J., Lyne, A. G., Madsen, E. C., McLaughlin, M. A., Patel, C., Scholz, P., Stairs, I. H., Stappers, B. W., and Zhu, W. W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on eight millisecond pulsars (MSPs) in binary systems discovered with the Arecibo PALFA survey. Phase-coherent timing solutions derived from 2.5 to 5 years of observations carried out at Arecibo and Jodrell Bank observatories are provided. PSR J1921+1929 is a 2.65-ms pulsar in a 39.6-day orbit for which we detect $\gamma$-ray pulsations in archival Fermi data. PSR J1928+1245 is a very low-mass-function system with an orbital period of 3.3 hours that belongs to the non-eclipsing black widow population. We also present PSR J1932+1756, the longest-orbital-period (41.5 days) intermediate-mass binary pulsar known to date. In light of the numerous discoveries of binary MSPs over the past years, we characterize the Galactic distribution of known MSP binaries in terms of binary class. Our results support and strengthen previous claims that the scatter in the Galactic scale height distribution correlates inversely with the binary mass function. We provide evidence of observational biases against detecting the most recycled pulsars near the Galactic plane, which overestimates the scale height of lighter systems. A possible bimodality in the mass function of MSPs with massive white dwarfs is also reported., Comment: Submitted to ApJ, 21 pages, 10 figures
Published: 2019
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49. CHIME/FRB Detection of Eight New Repeating Fast Radio Burst Sources

Author: Collaboration, The CHIME/FRB, Andersen, B. C., Bandura, K., Bhardwaj, M., Boubel, P., Boyce, M. M., Boyle, P. J., Brar, C., Cassanelli, T., Chawla, P., Cubranic, D., Deng, M., Dobbs, M., Fandino, M., Fonseca, E., Gaensler, B. M., Gilbert, A. J., Giri, U., Good, D. C., Halpern, M., Hill, A. S., Hinshaw, G., Höfer, C., Josephy, A., Kaspi, V. M., Kothes, R., Landecker, T. L., Lang, D. A., Li, D. Z., Lin, H. -H., Masui, K. W., Mena-Parra, J., Merryfield, M., Mckinven, R., Michilli, D., Milutinovic, N., Naidu, A., Newburgh, L. B., Ng, C., Patel, C., Pen, U., Pinsonneault-Marotte, T., Pleunis, Z., Rafiei-Ravandi, M., Rahman, M., Ransom, S. M., Renard, A., Scholz, P., Siegel, S. R., Singh, S., Smith, K. M., Stairs, I. H., Tendulkar, S. P., Tretyakov, I., Vanderlinde, K., Yadav, P., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on the discovery of eight repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources span a dispersion measure (DM) range of 103.5 to 1281 pc cm$^{-3}$. They display varying degrees of activity: six sources were detected twice, another three times, and one ten times. These eight repeating FRBs likely represent the bright and/or high-rate end of a distribution of infrequently repeating sources. For all sources, we determine sky coordinates with uncertainties of $\sim$10$^\prime$. FRB 180916.J0158+65 has a burst-averaged DM = $349.2 \pm 0.3$ pc cm$^{-3}$ and a low DM excess over the modelled Galactic maximum (as low as $\sim$20 pc cm$^{-3}$); this source also has a Faraday rotation measure (RM) of $-114.6 \pm 0.6$ rad m$^{-2}$, much lower than the RM measured for FRB 121102. FRB 181030.J1054+73 has the lowest DM for a repeater, $103.5 \pm 0.3$ pc cm$^{-3}$, with a DM excess of $\sim$ 70 pc cm$^{-3}$. Both sources are interesting targets for multi-wavelength follow-up due to their apparent proximity. The DM distribution of our repeater sample is statistically indistinguishable from that of the first 12 CHIME/FRB sources that have not repeated. We find, with 4$\sigma$ significance, that repeater bursts are generally wider than those of CHIME/FRB bursts that have not repeated, suggesting different emission mechanisms. Our repeater events show complex morphologies that are reminiscent of the first two discovered repeating FRBs. The repetitive behavior of these sources will enable interferometric localizations and subsequent host galaxy identifications., Comment: 40 pages, 11 figures; accepted by ApJL on 28 September 2019; added analysis of correlation between width and max. flux density
Published: 2019
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50. CHIME/FRB Detection of the Original Repeating Fast Radio Burst Source FRB 121102

Author: Josephy, A., Chawla, P., Fonseca, E., Ng, C., Patel, C., Pleunis, Z., Scholz, P., Andersen, B. C., Bandura, K., Bhardwaj, M., Boyce, M. M., Boyle, P. J., Brar, C., Cubranic, D., Dobbs, M., Gaensler, B. M., Gill, A., Giri, U., Good, D. C., Halpern, M., Hinshaw, G., Kaspi, V. M., Landecker, T. L., Lang, D. A., Lin, H. -H., Masui, K. W., Mckinven, R., Mena-Parra, J., Merryfield, M., Michilli, D., Milutinovic, N., Naidu, A., Pen, U., Rafiei-Ravandi, M., Rahman, M., Ransom, S. M., Renard, A., Siegel, S. R., Smith, K. M., Stairs, I. H., Tendulkar, S. P., Vanderlinde, K., Yadav, P., and Zwaniga, A. V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We report the detection of a single burst from the first-discovered repeating Fast Radio Burst source, FRB 121102, with CHIME/FRB, which operates in the frequency band 400-800 MHz. The detected burst occurred on 2018 November 19 and its emission extends down to at least 600 MHz, the lowest frequency detection of this source yet. The burst, detected with a significance of 23.7$\sigma$, has fluence 12$\pm$3 Jy ms and shows complex time and frequency morphology. The 34 ms width of the burst is the largest seen for this object at any frequency. We find evidence of sub-burst structure that drifts downward in frequency at a rate of -3.9$\pm$0.2 MHz ms$^{-1}$. Our best fit tentatively suggests a dispersion measure of 563.6$\pm$0.5 pc cm$^{-3}$, which is ${\approx}$1% higher than previously measured values. We set an upper limit on the scattering time at 500 MHz of 9.6 ms, which is consistent with expectations from the extrapolation from higher frequency data. We have exposure to the position of FRB 121102 for a total of 11.3 hrs within the FWHM of the synthesized beams at 600 MHz from 2018 July 25 to 2019 February 25. We estimate on the basis of this single event an average burst rate for FRB 121102 of 0.1-10 per day in the 400-800 MHz band for a median fluence threshold of 7 Jy ms in the stated time interval., Comment: Accepted in Astrophysical Journal Letters
Published: 2019
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