GCN Circular 43946
Subject
GRB 260307B: possible NOT optical counterpart
Event
Date
2026-03-08T12:01:24Z (3 days ago)
From
Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>
Via
Web form
G. Corcoran (UCD), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), S. Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration:
We observed the field of the SVOM GRB 260307B (Magnani et al., GCN 43940) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations consisted of 6x200 s in the SDSS-z band and started at 22:29:21 UT on March 7 2026 (about 8.7 hr after the SVOM trigger). The sky conditions were modest, with mediocre and variable seeing (1.6" in our stack), and the imaging sequence had to be interrupted. The mid-time of our combined observation was 9.46 hr after the SVOM trigger.
Within the SVOM/MXT localisation region reported by Magnani et al. (GCN 43940), we detect a faint source which visually is brighter than its archival counterpart in the Legacy survey. Its coordinates are:
RA (J2000) = 10:22:02.65
Dec (J2000) = -21:00:02.6
with an estimated error of ~0.5".
In our stacked images we measure a magnitude (AB) of:
z = 22.47 +/- 0.33
This magnitude is calibrated using nearby objects from the Pan-STARRS catalog and is not corrected for Galactic extinction. Photometry of this object on the Legacy survey images yields z = 23.27 +/- 0.22 AB. The source was thus brighter in the NOT images at the 2-sigma level (by 0.8 +/- 0.4 mag).
Given the low significance of the detection, we cannot securely claim the counterpart identification, and we invite to double-check the presence of this candidate in other data sets.