{
  "body": "A. Nicuesa Guelbenzu and S. Klose (both TLS Tautenburg) report:\n\nWe observed the field of the optical transient ZTF21aakruew/AT2021cwd (Yao\net al., GCN 29508) that was located inside the error box of GRB 210212B\n(Svinkin et al., GCN 29511) with GROND (Greiner et al. 2008, PASP 120,\n405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory\n(Chile).\n\nObservations were performed at 5:00 UT (midtime) on February 15, 2021,\nabout 3.1 days after the GRB 210212B trigger. They were executed at an\naverage seeing of 1.15 arcsec and at an average airmass of 1.3.\n\nThe optical transient is detected in the optical but not in the NIR bands.\nBased on a 33 min exposure in g'r'i'z' and 30 min in JHK, and we measure\nthe following preliminary AB magnitudes and upper limits (3 sigma):\n\ng' = 24.16 +/- 0.14,\nr' = 23.63 +/- 0.12,\ni' = 23.41 +/- 0.21,\nz' > 23.3,\nJ  > 21.7,\nH  > 21.1,\nK  > 18.1,\n\ncalibrated against SDSS and 2MASS field stars. The observed r'-band\nmagnitude is formally consistent with the observations reported by\nPozanenko et al. (GCN 29512).\n\nAfter correction for Galactic extinction (E(B-V)=0.04 mag; Ho et al., GCN\n29508), the data are in agreement with an SED that follows a power law. We\nconsider this as evidence that the transient was indeed afterglow light,\nconfirming its suggested association with GRB 210212B (Svinkin et al., GCN\n29511; Svinkin et al., GCN 29514).\n\n\nWe thank R. Lechaume (PUC) for performing the observations.",
  "eventId": "ZTF21aakruew",
  "subject": "ZTF21aakruew/AT2021cwd: GROND observations",
  "format": "text/plain",
  "createdOn": 1613650681000,
  "email": "ana@tls-tautenburg.de",
  "submitter": "Ana Nicuesa at TLS Tautenburg  <ana@tls-tautenburg.de>",
  "bibcode": "2021GCN.29528....1N",
  "version": 2,
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Tyler Barna at University of Minnesota <tylerpbarna@gmail.com>",
  "circularId": 29528,
  "editedOn": 1744224313282
}