{
  "bibcode": "2021GCN.30755....1N",
  "body": "A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg), and\nA. Rau (MPE Garching) report:\n\n\nWe observed the field of GRB 210901A (Swift trigger #1071488; Laha et al.,\nGCN 30746) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m\nMPG telescope at La Silla Observatory (Chile).\n\nObservations started at 23:43 UT on September 1, about 8.5 hr after the\nGRB trigger. They were performed at an average seeing of 2.3 arcsec and at\nan average airmass of 1.5.\n\nInside the 2.5 arcsec enhanced XRT error circle (Osborne et al., GCN\n30749), we do not detect any source. Based on an observation with 23.4\nminutes integration time in g'r'i'z' and 20 minutes in JHK, at a midtime\nof 23:43 UT on September 1, we measure the following preliminary 3-sigma\nupper limits (AB mags):\n\ng' > 23.5,\nr' > 23.6,\ni' > 22.6,\nJ  > 20.1,\nH  > 19.7, and\nK  > 16.3.\n\nWe note the presence of an object at the north-western border of the XRT\nerror circle at coordinates RA, DEC (J2000) = 19:41:05.98, -76:55:33.0 for\nwhich we measure r' = 21.33 +/- 0.05 mag (AB). Due to the relatively bad\nseeing at present we cannot decide with certainty if this is a galaxy or a\nstar.\n\nGiven magnitudes are calibrated against the SkyMapper catalog (Wolf et\nal., 2018, PASA 35, e010) in g'r'i'z' and 2MASS field stars in JHK\n(Skrutskie et al., 2006, AJ 131, 1163).\n\nWe thank Maren Hempel for excellent support and for performing the\nobservations.",
  "circularId": 30755,
  "createdOn": 1630687293000,
  "email": "ana@tls-tautenburg.de",
  "subject": "GRB 210901A: GROND observations",
  "submitter": "Ana Nicuesa at TLS Tautenburg  <ana@tls-tautenburg.de>",
  "eventId": "GRB 210901A"
}