GCN Circular 41096
Subject
EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
Event
Date
2025-07-15T12:48:10Z (3 months ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Via
Web form
EP250702a / GRB 250702BD,D,E: Hubble Space Telescope Observations
A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Saccardi (CEA/Irfu), P. O’Brien (Univ. of Leicester), R. A. J. Eyles-Ferris (Univ. of Leicester), A. de Ugarte Postigo (LAM), G. Corcoran (UCD), S. D. Vergani (LUX-Paris Obs.), N. R. Tanvir (U. Leicester), B. P. Gompertz (U. Birmingham) report for the Stargate collaboration:
We observed the location of EP250702a / GRB 250702B,D,E (Cheng et al., GCNs 40906, 40917; Fermi GBM Team, GCNs 40883, 40886, 40890; DeLaunay et al., GCN 40903; Frederiks et al., GCN 40914) with the Hubble Space Telescope on 15 July 2025. A total of 2196 s of observations were obtained using WFC3 and the F160W (broad-band H) filter.
At the location of the infrared counterpart (Martin-Carrillo et al., GCN 40924; Levan et al., GCN 40961) we clearly resolve a galaxy, whose nucleus is offset 0.7” from the transient location. The galaxy has an edge-on morphology, and either a disturbed disc or prominent dust lane. The transient lies on the stellar field of this galaxy, and the low probability of chance alignment (0.05%: Levan et al., GCN 40961) strongly implies that EP250702a / GRB 250702BDE is indeed an extragalactic transient. A weak excess of emission over the smooth disc is present at the transient location, but it appears likely the flux is now dominated by galaxy light.
If extragalactic in origin the very long duration of the outburst is extremely unusual. Only relativistic TDEs have been seen to have such long-lived emission in gamma-rays. However, the non-nuclear nature of the transient is not in keeping with the expected location of a supermassive black hole, although is consistent with the expectations for white-dwarf - intermediate mass black hole disruptions.
We thank Bill Januszewski, Joel Green, Claus Leitherer and Jennifer Lotz for their rapid work in approving and scheduling these observations.