{
  "bibcode": "2021GCN.30584....1N",
  "body": "A. Nicuesa Guelbenzu, S. Klose, S. Schmidl (all TLS Tautenburg), A. Rau\n(MPE Garching), and D. A. Kann (HETH/IAA-CSIC) report:\n\nUsing GROND mounted at the 2.2m MPG telescope at ESO La Silla Observatory\n(Chile), we continued to observe the bright afterglow of GRB 210731A\n(Swift trigger 1062336; Troja et al., GCN 30568).\n\nA comparison of our first-epoch optical data (Nicuesa Guelbenzu et al.,\nGCN 30574) with those from de Wet et al. (GCN 30570) indicated that the\noptical afterglow underwent a relatively long-lasting plateau phase (see\nalso Zhen & Filippenko, GCN 30582). Our 2nd epoch GROND observations now\nreveal that this plateau phase has finished and the afterglow has entered\na declining phase.\n\nAt a mean time of 1.22 days post burst we measure (AB magnitudes)\n\nr' = 20.74 +/- 0.02 mag,\n\ncalibrated against the Pan-STARRS catalog. This is in good agreement with\nthe VLT X-shooter result at 1.19 d (Kann et al., GCN 30583).\n\n\nWe thank Sam Kim for excellent support and for performing the\nobservations.",
  "circularId": 30584,
  "createdOn": 1627916810000,
  "email": "ana@tls-tautenburg.de",
  "subject": "GRB 210731A: continued GROND observations",
  "submitter": "Ana Nicuesa at TLS Tautenburg  <ana@tls-tautenburg.de>",
  "eventId": "GRB 210731A"
}