{
  "bibcode": "2011GCN.11949....1A",
  "body": "P. Afonso (MPE Garching), A. Rossi, S. Klose (TLS Tautenburg), and J. \nGreiner (MPE Garching) report on behalf of the GROND team:\n\nWe observed the field of GRB 110420B (Swift trigger 451794; Sbarufatti et\nal. GCN 11944) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.\n2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope on La Silla.\n\nObservations started at 7:00 UT on April 21, 8.15 hours after the GRB \ntrigger. They were obtained under challenging sky conditions, with a \nseeing > 1.5 arcsec, an average airmass of 1.7, bright moonlight, and \npassing cirrus.\n\nIn a first epoch, centered on the refined BAT error circle (Markwardt et \nal., GCN 11946), we do not detect any new object \ndown to the DSS2 limit. The XRT error circle (Sbarufatti et al., GCN \n11947) was not covered by these observations in g'r'i'z'.\n\nA subsequent epoch started about 30 min later and was centered on the XRT \nafterglow candidate (Sbarufatti et al., GCN 11947). Here we note the \npresence of a relatively bright object at the border of the XRT error \ncircle at coordinates RA, DEC (J2000) 21:20:25.389, -41:17:51.79 (+/- 0.5 \narcsec), which could be a galaxy seen nearly face-on. This object is also \nvisible in the DSS2-red image.  Unfortunately, due to the bad seeing we \ncannot decide with certainty at the moment if this object is a galaxy or a \nstar. Its r'-band magnitude is r'(AB)  = 19.5 +/- 0.1. No other source is \ndetected inside the XRT error circle down to r'(AB) = 23.2.\n\nMagnitudes are derived by calibrating the images against GROND zeropoints \nand 2MASS field stars. We note that the Galactic reddening along the line \nof sight is E(B-V) = 0.03 mag (Schlegel et al. 1998).",
  "circularId": 11949,
  "createdOn": 1303389344000,
  "email": "rossi@tls-tautenburg.de",
  "subject": "GRB 110420B, GROND observations",
  "submitter": "Andrea Rossi at TLS Tautenburg  <rossi@tls-tautenburg.de>",
  "eventId": "GRB 110420B"
}