JWST Spectroscopy of GRB 250702B: An Extremely Rare and Exceptionally Energetic Burst in a Dusty, Massive Galaxy at z = 1.036

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Gompertz, BP orcid iconORCID: 0000-0002-5826-0548, Levan, AJ orcid iconORCID: 0000-0001-7821-9369, Laskar, T orcid iconORCID: 0000-0003-1792-2338, Schneider, B orcid iconORCID: 0000-0003-4876-7756, Chrimes, AA orcid iconORCID: 0000-0001-9842-6808, Martin-Carrillo, A orcid iconORCID: 0000-0001-5108-0627, Sneppen, A orcid iconORCID: 0000-0002-5460-6126, O’Neill, D orcid iconORCID: 0009-0001-1554-1868, Malesani, DB orcid iconORCID: 0000-0002-7517-326X, Jonker, PG orcid iconORCID: 0000-0001-5679-0695, Burns, E orcid iconORCID: 0000-0002-2942-3379, Corcoran, G orcid iconORCID: 0009-0009-1573-8300, Cotter, L orcid iconORCID: 0000-0002-7910-6646, de Ugarte Postigo, A orcid iconORCID: 0000-0001-7717-5085, De Pasquale, M orcid iconORCID: 0000-0002-4036-7419, Dimple orcid iconORCID: 0000-0001-9868-9042, Eyles-Ferris, RAJ orcid iconORCID: 0000-0002-8775-2365, Fruchter, A orcid iconORCID: 0000-0002-6652-9279, Izzo, L orcid iconORCID: 0000-0001-9695-8472, Jakobsson, P orcid iconORCID: 0000-0002-9404-5650 et al (2026) JWST Spectroscopy of GRB 250702B: An Extremely Rare and Exceptionally Energetic Burst in a Dusty, Massive Galaxy at z = 1.036. The Astrophysical Journal Letters, 997 (1). ISSN 2041-8205

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Abstract

We present follow-up observations of the day-long, repeating gamma-ray burst (GRB) GRB 250702B with the Near Infrared Spectrograph on board the James Webb Space Telescope. Through the identification of narrow hydrogen emission lines at a consistent redshift of z = 1.036 ± 0.004, we calibrate the distance scale, and therefore the energetics, of this unique extragalactic transient. At this distance, the resulting γ-ray energy release is at least Eγ,iso = 2.2 × 1054 erg. We find no evidence for ongoing transient emission at the GRB position and exclude any accompanying supernova (SN) with a luminosity comparable to the Type Ic broad-line SN 2023lcr, though we are unable to rule out a fainter SN counterpart owing to high extinction. The inferred rate of such events, assuming at most one in the lifetime of Fermi, suggests that such bursts are very rare, with volumetric rates over 1000 times lower than normal high-luminosity long GRBs and >105 times lower than core-collapse SNe, when corrected for beaming. Furthermore, we find that the host galaxy is unique among GRB host galaxies and extremely rare in the general galaxy population, being extremely large and dusty and with high stellar mass. The identification of such an exotic GRB in such an unusual galaxy raises the possibility that the environment was important in the progenitor channel creating GRB 250702B.

Item Type: Article
Uncontrolled Keywords: 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5109 Space sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
Date of acceptance: 17 December 2025
Date of first compliant Open Access: 5 June 2026
Date Deposited: 05 Jun 2026 13:24
Last Modified: 05 Jun 2026 13:24
DOI or ID number: 10.3847/2041-8213/ae2ed9
URI: https://researchonline.ljmu.ac.uk/id/eprint/28748
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