GCN Circular 29149
Subject
GRB 201221A: REM early-time afterglow detection
Date
2020-12-23T14:46:01Z (3 years ago)
From
Paolo D'Avanzo at INAF-OAB <pda.davanzo@gmail.com>
P. D'Avanzo, S. Covino, D. Fugazza, A. Melandri (INAF-OAB), D. B. Malesani (DTU space)
on behalf of the REM team, report:
We observed the field of GRB 201221A (Page et al., GCN Circ. 29096) with the REM 60cm robotic
telescope located at the ESO premise of La Silla (Chile). The observations were performed starting
on 2020 December 21 at 07:10:33 UT (i.e. 92 seconds after the burst) and were carried in the g, r, i, z
bands simultaneously.
From preliminary photometry, we estimate the following magnitudes and 3sigma upper limits for the
afterglow reported by Malesani et al. (GCN Circ. 29100):
g > 17.9
r > 17.8
i > 17.7
z = 15.8 +/- 0.3
(AB; calibrated against the APASS catalogues), at a mean time of 97 seconds after the GRB t0.
By combining our z-band magnitude with the one reported by Malesani et al., we infer an afterglow
temporal decay (f propto t^(alpha)) of alpha ~ -1.2 between 97 seconds and 2100 seconds after the GRB t0.