GCN Circular 30584
Subject
GRB 210731A: continued GROND observations
Date
2021-08-02T15:06:50Z (3 years ago)
From
Ana Nicuesa at TLS Tautenburg <ana@tls-tautenburg.de>
A. Nicuesa Guelbenzu, S. Klose, S. Schmidl (all TLS Tautenburg), A. Rau
(MPE Garching), and D. A. Kann (HETH/IAA-CSIC) report:
Using GROND mounted at the 2.2m MPG telescope at ESO La Silla Observatory
(Chile), we continued to observe the bright afterglow of GRB 210731A
(Swift trigger 1062336; Troja et al., GCN 30568).
A comparison of our first-epoch optical data (Nicuesa Guelbenzu et al.,
GCN 30574) with those from de Wet et al. (GCN 30570) indicated that the
optical afterglow underwent a relatively long-lasting plateau phase (see
also Zhen & Filippenko, GCN 30582). Our 2nd epoch GROND observations now
reveal that this plateau phase has finished and the afterglow has entered
a declining phase.
At a mean time of 1.22 days post burst we measure (AB magnitudes)
r' = 20.74 +/- 0.02 mag,
calibrated against the Pan-STARRS catalog. This is in good agreement with
the VLT X-shooter result at 1.19 d (Kann et al., GCN 30583).
We thank Sam Kim for excellent support and for performing the
observations.