GCN Circular 40924
Subject
GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
Event
Date
2025-07-03T18:17:16Z (13 hours ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
A. Martin-Carrillo (UCD), A. J. Levan (Radboud), B. Schneider (LAM), J. An (NAOC), D. Xu (NAOC), S. Campana (INAF-OAB), G. Corcoran (UCD), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the Stargate collaboration:
We observed the location of EP250702a (Cheng et al., GCNs 40906, 40917) likely associated with GRB 250702B,C,D,E detected by Fermi/GBM (Fermi GBM Team, GCNs 40883, 40885, 40886, 40890), Swift/BAT (via de GUANO system; DeLaunay et al., GCN 40903) and Konus/Wind (Frederiks et al., GCN 40914), all likely originating from the same astrophysical source (Neights et al., GCN 40891). We used the ESO VLT UT4 (Yepun) equipped with the HAWK-I near-infrared camera. We obtained two 20 min exposures in each of the H and K bands, starting on 2025 July 3 at 07:03:03 UT (17.1 hr after the first Fermi trigger, GRB 250702B).
At the location of the UVOT-enhanced (2" radius) coordinates provided by Swift/XRT (Kennea et al., GCN 40919) we identify a bright source not visible in archival H and K images from VISTA/VHS and UKIDSS at the following coordinates (J2000):
RA (J2000) = 18:58:45.57
Dec (J2000) = -07:52:26.2
with an uncertainty of ~0.5" in each axis. The source has a magnitude of K ~ 17.3 (Vega), calibrated against 2MASS stars.
We note that, while the source is dominated by point-like emission, it appears to be extended along the E-W direction. As this is a crowded field, this could be just the result of source confusion. Alternatively, if the extension is real, it could be related to nebulosity around a Galactic source, or be a distant host galaxy which would imply an extragalactic origin for GRBs 250702B,C,D,E / EP250702a.
Further observations are planned and encouraged to reveal the nature of this unusual gamma-ray burster.
We acknowledge excellent support from the observing staff in Paranal, in particular Marco Berton, Robert Klement, Susana Cerda-Hernandez, Thomas Rivinius, and Thomas Szeifert.