Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud

Wang, Y., et al.
We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ∼20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm-3, and rotation measure (RM) of +456 rad m-2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523-7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ∼1 mJy at 1400 MHz and ∼25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ -3, where S ν ∝ ν α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds.
Y.W. is supported by the China Scholarship Council. T.M. acknowledges the support of the Australian Research Council (ARC) through grant DP190100561. DK and AO are supported by NSF grant AST-1816492. V.G., N.R., and M.R. acknowledge support from the H2020 ERC Consolidator Grant "MAGNESIA" under grant agreement Nr. 817661 (PI: Rea), and grants SGR2017-1383 and PGC2018-095512-B-I00. R.M.S. acknowledges support through ARC Future Fellowship FT 190100155. A.R. gratefully acknowledges financial support by the research grant "iPeska" (PI: Andrea Possenti) funded under the INAF national call Prin-SKA/CTA approved with the Presidential Decree 70/2016 and continuing valuable support from the Max-Planck Society. AR also acknowledges support from the Ministero degli Affari Esteri e della Cooperazione Internazionale—Direzione Generale per la Promozione del Sistema Paese—Progetto di Grande Rilevanza ZA18GR02. G.R.S. is supported by NSERC Discovery Grants RGPIN-2016-06569 and RGPIN-2021-0400. This research was supported by the Sydney Informatics Hub (SIH), a core research facility at the University of Sydney.