GCN Circular 44728
Subject
GRB 260527A/EP260527a: FTW optical and NIR observations
Event
Date
2026-05-28T23:03:55Z (21 hours ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Brendan O'Connor (CMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander Hall (CMU), and Antonella Palmese (CMU) report:
We observed the counterpart of GRB 260527A/EP260527a (Yang et al., GCN 44718; Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726; Mo et al., GCN 44727) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J-band simultaneously for 45 x 180 s starting at 2026-05-28T19:58:32 UT (1.57 days after the trigger). We detect the counterpart at
r = (23.1 +/- 0.2) AB mag,
calibrated against the PS1 catalog and not corrected for the Galactic extinction of A_V = 0.050 mag (Schlafly & Finkbeiner 2011).
We note that there is a potential host galaxy with a DESI DR1 (DESI Collaboration et al., 2026, AJ, 171, 285) redshift of z = 0.3656 located ~13" North-East from the afterglow position. At this redshift, the projected physical offset is ~66 kpc, which is at the high end of the distribution of short GRB offsets but not unprecedented (O'Connor 2022, MNRAS, 515, 4890). We derive a probability of chance coincidence of Pcc~0.09, suggesting a possible association. However, as this is a very large offset, deep imaging may reveal additional candidate host galaxies. We do note that based on the available DESI DR1 spectra, there appears to be an overdensity of z~0.36 galaxies along this line-of-sight, suggesting a possible origin within or intersection with a low redshift galaxy cluster (Dichiara et al., 2026, ApJL, 999, L42).
The spectrum can be viewed at: https://www.legacysurvey.org/viewer/desi-spectrum/dr1/targetid39627824205661166.
We thank Christoph Ries for obtaining the observations.