Optical/Infrared Observations of the Extraordinary GRB 250702B: A Highly Obscured Afterglow in a Massive Galaxy Consistent with Multiple Possible Progenitors

Abstract

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank the anonymous referee for their thoughtful feedback and suggestions that strengthened this work.

We thank Brian Lemaux, staff scientist at Gemini North, for his exceptional assistance throughout this project. His expertise, dedication, and willingness to provide rapid advice across often inconvenient time zones were invaluable to the success of this work. We also thank Chris Simpson for his timely assistance with edge case GMOS reductions. J.C., I.A., and B.O. acknowledge useful discussions with Eliza Neights and Eric Burns and thank Ben Gompertz, Andrew Levan, and Antonio Martin-Carrillo for sharing the redshift derived by JWST.

The Andreoni Transient Astronomy Lab is supported by the National Science Foundation award AST 2505775, NASA grant 24-ADAP24-0159, and the Discovery Alliance Catalyst Fellowship Mentors award 2025-62192-CM-19. B.O. is supported by the McWilliams Postdoctoral Fellowship in the McWilliams Center for Cosmology and Astrophysics at Carnegie Mellon University. M.B. is supported by a Student grant from the Wübben Stiftung Wissenschaft. W.Z. acknowledges the support from the Harvard–Smithsonian Center for Astrophysics through the CfA Fellowship. E.R.C. acknowledges support from NASA through the Astrophysics Theory Program, grant 80NSSC24K0897. P.B.’s work was funded by a grant (No. 2020747) from the United States–Israel Binational Science Foundation (BSF), Jerusalem, Israel, and by a grant (No. 1649/23) from the Israel Science Foundation. P.C. acknowledges the support from the Zhejiang provincial top-level research support program. C.D.K. gratefully acknowledges support from the NSF through AST-2432037, from the HST Guest Observer Program through HST-SNAP-17070 and HST-GO-17706, and from JWST Archival Research through JWST-AR-6241 and JWST-AR-5441. A.P. is supported by NSF grant No. 2308193.

This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This Letter contains data obtained at the Wendelstein Observatory of the Ludwig-Maximilians University Munich. Funded in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy—EXC-2094—390783311. This work is based on observations made with the NASA/ESA Hubble Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. This research is based on data obtained from the Astro Data Archive at NSF NOIRLab. NOIRLab is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the US National Science Foundation. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. Funding for the DES Projects has been provided by the US Department of Energy, the US National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at The Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico and the Ministerio da Ciencia, Tecnologia e Inovacao, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the Dark Energy Survey.

Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. Based on observations at Cerro Tololo Inter-American Observatory, NSF’s NOIRLab (NOIRLab Prop. ID 2025A-729671; PI: Palmese), which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. Based on observations obtained at the international Gemini Observatory, a program of NSF’s OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). The data were acquired through the Gemini Observatory Archive at NSF NOIRLab and processed using Data Reduction for Astronomy from Gemini Observatory North and South (DRAGONS).

The Collaborating Institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, the Eidgenossische Technische Hochschule (ETH) Zurich, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Institut de Ciencies de l’Espai (IEEC/CSIC), the Institut de Fisica d’Altes Energies, Lawrence Berkeley National Laboratory, the Ludwig Maximilians Universitat Munchen and the associated Excellence Cluster Universe, the University of Michigan, NSF NOIRLab, the University of Nottingham, The Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A&M University.

Data Availability

The HST data presented in this Letter were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via DOI: 10.17909/12kv-9c88.

Software References

Software: Astropy (Astropy Collaboration et al. 2013, 2018, 2022), matplotlib (J. D. Hunter 2007), SWarp (E. Bertin 2025), Source Extractor (E. Bertin & S. Arnouts 1996), Morfometryka (F. Ferrari et al. 2015), GALFIT (C. Y. Peng et al. 2002), DRAGONS (K. Labrie et al. 2019), Photutils (P. Bradley et al. 2024), VegasAfterglow (Y. Wang et al. 2025), astrometry.net (D. Lang et al. 2010), dynesty (J. S. Speagle 2020), DrizzlePac, emcee (D. Foreman-Mackey et al. 2013), bilby (G. Ashton et al. 2019), Claude (Anthropic 2024).