A Radio Flare in the Long-lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?

Schroeder, GenevieveGenevieveSchroeder0000-0001-9695-8472Rhodes, LaurenLaurenRhodesLaskar, TanmoyTanmoyLaskarNugent, AnyaAnyaNugentRouco Escorial, AliciaAliciaRouco EscorialRastinejad, Jillian C.Jillian C.RastinejadFong, Wen-faiWen-faiFongvan der Horst, Alexander J.Alexander J.van der HorstVeres, PéterPéterVeresAlexander, Kate D.Kate D.AlexanderAndersson, AlexAlexAnderssonBerger, EdoEdoBergerBlanchard, Peter K.Peter K.BlanchardChastain, SarahSarahChastainChristensen, LiseLiseChristensenFender, RobRobFenderGreen, David A.David A.GreenGroot, PaulPaulGrootHeywood, IanIanHeywoodHoresh, AssafAssafHoreshIzzo, LucaLucaIzzoKilpatrick, Charles D.Charles D.KilpatrickKörding, ElmarElmarKördingLien, AmyAmyLienMalesani, Daniele B.Daniele B.MalesaniMcBride, VanessaVanessaMcBrideMooley, KunalKunalMooleyRowlinson, AntoniaAntoniaRowlinsonSears, HueiHueiSearsStappers, BenBenStappersTanvir, NialNialTanvirVergani, Susanna D.Susanna D.VerganiWijers, Ralph A. M. J.Ralph A. M. J.WijersWilliams-Baldwin, DavidDavidWilliams-BaldwinWoudt, PatrickPatrickWoudt2024-12-092024-12-092024http://hdl.handle.net/20.500.12386/40234We present the discovery of the radio afterglow of the short gamma-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of z ∼ 2.4. While radio observations commenced ≲1 day after the burst, no radio emission was detected until ∼11 days. The radio afterglow subsequently brightened by a factor of ∼3 in the span of a week, followed by a rapid decay (a "radio flare"). We find that a forward shock afterglow model cannot self-consistently describe the multiwavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of ≈5. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of ≈4, or a reverse shock from a shell collision are viable solutions to match the broadband behavior. At z ∼ 2.4, GRB 210726A is among the highest-redshift short GRBs discovered to date, as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by ≲10 days after the burst, potentially missing these late-rising, luminous radio afterglows.Gamma-ray burstsHigh energy astrophysicsRadio astronomyTime domain astronomy62973913382109Astrophysics - High Energy Astrophysical PhenomenaA Radio Flare in the Long-lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?article10.3847/1538-4357/ad49ab10.48550/arXiv.2308.109362024ApJ...970..139S