Optical/Infrared Observations of the Extraordinary GRB 250702B: A Highly Obscured Afterglow in a Massive Galaxy Consistent with Multiple Possible Progenitors
Abstract GRB 250702B was the longest gamma-ray burst ever detected, with a duration that challenges standard collapsar models and suggests an exotic progenitor. We collected a rich set of optical and infrared follow-up observations of its rapidly fading afterglow using a suite of telescopes including the W. M. Keck Observatory, the Gemini telescopes, the Magellan Baade Telescope, the Victor M. Blanco 4 m telescope, and the Fraunhofer Telescope at Wendelstein Observatory. Our analysis reveals that the afterglow emission is well described by forward shock emission from a highly obscured relativistic jet. Deep photometric observations of the host galaxy reveal a massive (10 10.66 M ⊙ ), dusty, and extremely asymmetric system that is consistent with two galaxies undergoing a major merger. The galactocentric offset, host galaxy properties, and jet characteristics disfavor a jetted tidal disruption event (TDE) around a supermassive black hole but do not definitively distinguish between competing progenitor scenarios. We find that the afterglow and host are consistent with a range of progenitors, including an atypical collapsar, a merger between a helium star and a stellar-mass black hole, the disruption of a star by a stellar-mass compact object (micro-TDE), and the tidal disruption of a star by an off-nuclear intermediate-mass black hole.
Authors
- C. D. Kilpatrick (ORCID: https://orcid.org/0000-0002-5740-7747)
- Silona Wilke
- G. Damke (ORCID: https://orcid.org/0000-0002-2651-7038)
- Weicheng Zang (ORCID: https://orcid.org/0000-0001-6000-3463)
- Xander J. Hall (ORCID: https://orcid.org/0000-0002-9364-5419)
- Kritti Sharma (ORCID: https://orcid.org/0000-0002-4477-3625)
- Jonathan Carney (ORCID: https://orcid.org/0000-0001-8544-584X)
- D. Gruen (ORCID: https://orcid.org/0000-0003-3270-7644)
- A. Riffeser (ORCID: https://orcid.org/0000-0002-5466-3892)
- Akash Anumarlapudi (ORCID: https://orcid.org/0000-0002-8935-9882)
- Steve Heathcote (ORCID: https://orcid.org/0000-0002-0856-3663)
- Hank Corbett (ORCID: https://orcid.org/0000-0002-6339-6706)
- Ramandeep Gill (ORCID: https://orcid.org/0000-0003-0516-2968)
- James Freeburn (ORCID: https://orcid.org/0009-0006-7990-0547)
- Christopher J. Conselice (ORCID: https://orcid.org/0000-0003-1949-7638)
- Kaustav K. Das (ORCID: https://orcid.org/0000-0001-8372-997X)
- Nicholas M. Law (ORCID: https://orcid.org/0000-0001-9380-6457)
- A. Palmese (ORCID: https://orcid.org/0000-0002-6011-0530)
- Brendan O’Connor (ORCID: https://orcid.org/0000-0002-9700-0036)
- A. Gal‐Yam (ORCID: https://orcid.org/0000-0002-3653-5598)
- Lei Hu (ORCID: https://orcid.org/0000-0001-7201-1938)
- Kathleen Labrie (ORCID: https://orcid.org/0000-0002-6633-7891)
- Igor Andreoni (ORCID: https://orcid.org/0000-0002-8977-1498)
- Eric R. Coughlin (ORCID: https://orcid.org/0000-0003-3765-6401)
- Hannah Skobe (ORCID: https://orcid.org/0000-0003-0516-3485)
- Dheeraj R. Pasham (ORCID: https://orcid.org/0000-0003-1386-7861)
- Paz Beniamini (ORCID: https://orcid.org/0000-0001-7833-1043)
- Viraj Karambelkar (ORCID: https://orcid.org/0000-0003-2758-159X)
- M. J. Schmidt (ORCID: https://orcid.org/0009-0003-1323-9774)
- Tomás Ahumada (ORCID: https://orcid.org/0000-0002-2184-6430)
- Lewi Westcott (ORCID: https://orcid.org/0009-0008-8642-5275)
- Ping Chen (ORCID: https://orcid.org/0000-0003-0853-6427)
- M. M. Kasliwal (ORCID: https://orcid.org/0000-0002-5619-4938)
- Malte Busmann (ORCID: https://orcid.org/0009-0001-0574-2332)
Institutions
- Northwestern University (US)
- University of North Carolina at Chapel Hill (US)
- California Institute of Technology (US)
- Open University of Israel (IL)
- George Washington University (US)
- University of Manchester (GB)
- Excellence Cluster Origins (DE)
- Gemini North Observatory (US)
- Center for Astrophysics Harvard & Smithsonian (US)
- Cerro Tololo Inter-American Observatory (CL)
- Eureka Scientific (US)
- Weizmann Institute of Science (IL)
- Syracuse University (US)
- Carnegie Mellon University (US)
- Zhejiang University (CN)
- Ludwig-Maximilians-Universität München (DE)
- Universidad Nacional Autónoma de México (MX)
Publication Details
- Journal
- The Astrophysical Journal Letters
- Published
- 2025-11-26
- DOI
- https://doi.org/10.3847/2041-8213/ae1d67
- Citations
- 3
- Primary Topic
- Gamma-ray bursts and supernovae
- Type
- article
- Field-Weighted Citation Impact
- 3.46