{
  "bibcode": "2021GCN.30781....1N",
  "body": "A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg), and A. Rau (MPE \nGarching) report:\n\nWe observed the field of GRB 210905A (Swift trigger #1071993; Sonbas et \nal., GCN 30765) simultaneously in g'r'i'z'JHK with GROND mounted at the \n2.2m MPG telescope at La Silla Observatory (Chile).\n\nObservations started at 23:35 UT on September 5, about 23.2 hr after the \nGRB trigger. They were performed at an average seeing of 1.7 arcsec and at \nan average airmass of 1.2.\n\nBased on combined images with 22 min total exposure in g'r'i'z' and 25 min \nin JHK, at a mid-time of 23:55 UT on 2021-09-05 for the afterglow \n(Strausbaugh & Cucchiara GCN 30769 and 30770; Tanvir et al., GCN 30771; \nD'Avanzo et al., GCN 30772; Dobie et al., GCN 30773) we derive the \nfollowing preliminary AB magnitudes and 3-sigma upper limits:\n\ng' > 24.3,\nr' > 24.3,\ni' > 23.8,\nz' = 21.6 +/- 0.2,\nJ  = 20.2 +/- 0.2,\nH  = 20.1 +/- 0.2,\nK  > 18.2.\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 and Regis Lachaume for excellent support and for \nperforming the observations.",
  "circularId": 30781,
  "createdOn": 1630947840000,
  "email": "klose@tls-tautenburg.de",
  "subject": "GRB 210905A, GROND observations",
  "submitter": "Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>",
  "eventId": "GRB 210905A"
}