GCN Circular 45957
Subject
GRB261010A: Keck/MOSFIRE detection of a near-IR source
Event
Date
2026-10-16T06:42:59Z (9 hours ago)
From
Jillian Rastinejad at University of Maryland <jillianrastinejad2024@u.northwestern.edu>
Via
Web form
Jillian Rastinejad (UMD), Maggie Li, and Mansi Kasliwal (Caltech) report on behalf of a larger collaboration:
We observed the location of GRB 261010A (Fermi GBM Team, GCN 45888; Lien et al., GCN 45889, Frederiks et al. GCN 45925) using the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) mounted on the Keck I Telescope. We obtained 73 x 40-sec imaging in J-band at a mid-time of 05:17 UT on 2026 Oct 16 (5.4 days post-burst) at seeing of ~0.7”.
We detect a near-IR source at >3 sigma significance that is consistent with the position of the optical afterglow (O’Neill et al., GCN 45890; Aceituno et al., GCN 45891; Corcoran et al., GCN 45912). Precise photometry is complicated by contamination from the nearby galaxy, but we roughly measure a J-band magnitude that is consistent with the reported LBT measurement of H = 24.0 +/- 0.3 AB mag (Marchesini et al. GCN 45952). We observe a slight offset (< 0.5”) to the North between the reported optical afterglow position (O’Neill et al., GCN 45890) and the near-IR source in our MOSFIRE imaging. Given the lack of variability, we are unable to conclude if this emission is due to the counterpart of GRB 261010A or is due to an underlying galaxy.
We thank the Keck staff, including Julie Renaud-Kim and Josh Walawender, and the Keck classical night observers, including Gillian Willson for their co-operation with the ToO observations.