GRB 250704B: An Off-axis Short GRB with a Long-lived Afterglow Plateau

Abstract

Copyright and License

© 2026. 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 the comments and suggestions that have helped us to improve the Letter.

We thank all members of the GROWTH collaboration for helping with observations and data processing.

GIT (H. Kumar et al. 2022) is a 70 cm telescope with a 07 field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (IAO; Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.

This work is partially based on data obtained with the 2 m HCT of IAO under the proposal 2025-02-P10 (PI: D. Eappachen). We thank the staff of IAO, Hanle, and CREST, Hosakote, who made these observations possible. The facilities at IAO and CREST are operated by the Indian Institute of Astrophysics, Bangalore. We thank the staff of the GMRT who made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 nonprofit organization 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 Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

M.W.C. acknowledges support from the National Science Foundation with grant Nos. PHY-2117997, PHY-2308862, and PHY-2409481.

N.S. is supported by a fellowship from the Kavli Foundation.

A.P. acknowledges support by the National Science Foundation AST grant No. 2308193. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. 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.

M.K. and V.B. acknowledge the support from the VAIBHAV Fellowship of the Department of Science and Technology of the Government of India.

V.B. and the IIT Bombay team sincerely thank BDP UGL Global Logistics Pvt. Ltd. for their generous CSR support toward our computational needs.

We thank Anirudh Salgundi and Arjun Ghosh for help with the Chandra proposal. We thank Ashwin Devaraj for useful discussions.

G.C.A. thanks the Indian National Science Academy (INSA) for support under their Senior Scientist Programme.

The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application packages CIAO.

S.A. is supported by an LSST-DA Catalyst Fellowship, funded through the support of grant 62192 from the John Templeton Foundation to LSST-DA. S.A. also gratefully acknowledges support from Stanford University, the US Department of Energy, and Fred Kavli and the Kavli Foundation.

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.

Funded in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy–EXC-2094–390783311.

Facilities

Swift - Swift Gamma-Ray Burst Mission (XRT), Chandra - , GIT - , HCT - Himalayan Chandra Telescope, Keck:I - KECK I Telescope, Blanco - Cerro Tololo Inter-American Observatory's 4 meter Blanco Telescope, WO:2m (FTW) - , Hale (Palomar 200-inch telescope) - , PO:1.5 (Palomar 60-inch telescope) - , GMRT - Giant Meter-wave Radio Telescope.

Software References

Astropy (Astropy Collaboration et al. 2013, 2018; Astropy Collaboration et al. 2022), Source Extractor (E. Bertin & S. Arnouts 1996), Astro-SCRAPPY (C. McCully & M. Tewes 2019), solve-field astrometry engine (D. Lang et al. 2010), PSFEx (E. Bertin 2013), jetsimpy (H. Wang et al. 2024), ciao-4.15 (A. Fruscione et al. 2006), afterglowpy (G. Ryan et al. 2020, 2024), PyMultiNest (J. Buchner et al. 2014), CASA (Team CASA et al. 2022).

Contributions

All authors contributed equally to this collaborative work.