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A millimeter rebrightening in GRB 210702A

S. de WetUniversity of Cape Town Astronomy Department , Private Bag X3 , Rondebosch , 7701 , South AfricaT. LaskarDepartment of Physics & Astronomy , University of Utah , Salt Lake City , UT 84112 , USAP. GrootRodolfo Barniol DuranDepartment of Physics and Astronomy , California State University , Sacramento , 6000 J Street , Sacramento , CA 95819-6041 , USAE. BergerCenter for Astrophysics | Harvard & Smithsonian , 60 Garden St , Cambridge , MA 02138 , USAShivani BhandariTarraneh EftekhariCenter for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy , Northwestern University , Evanston , IL 60208 , USAC. GuidorziS. KobayashiAstrophysics Research Institute , Liverpool John Moores University , 146 Brownlow Hill , Liverpool L3 5RF , UKD. A. PerleyAstrophysics Research Institute , Liverpool John Moores University , 146 Brownlow Hill , Liverpool L3 5RF , UKR. SariRacah Institute of Physics , The Hebrew University of Jerusalem , 91904 , IsraelGenevieve SchroederCenter for Interdisciplinary Exploration and Research in Astrophysics and

2024en

ABI

Annotatsiya

We present X-ray to radio frequency observations of the bright long gamma-ray burst GRB 210702A. Our ALMA 97.5 GHz observations show a significant rebrightening by a factor of ~2 beginning at 8.2 days post-burst and rising to peak brightness at 18.1 days before declining again. This is the first such rebrightening seen in a millimeter afterglow light curve. A standard forward shock model in a stellar wind circumburst medium can explain most of our X-ray, optical and millimeter observations prior to the rebrightening, but significantly over-predicts the self-absorbed radio emission, and cannot explain the millimeter rebrightening. We investigate possible explanations for the millimeter rebrightening and find that energy injection or a reverse shock from a late-time shell collision are plausible causes. Similar to other bursts, our radio data may require alternative scenarios such as a thermal electron population or a structured jet to explain the data. Our observations demonstrate that millimeter light curves can exhibit some of the rich features more commonly seen in optical and X-ray afterglow light curves, motivating further millimeter wavelength studies of GRB afterglows.

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DOI: 10.48550/arxiv.2408.14641

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