{
  "bibcode": "2016GCN.19975....1C",
  "body": "T.-W. Chen (MPE Garching), S. Klose, A. Nicuesa Guelbenzu (TLS), \nJ. Bolmer (MPE Garching and ESO Vitacura), T. Kruehler and \nJ. Greiner (both MPE Garching) report on behalf of the GROND team:\n\nWe observed the field of GRB 161001A (Swift trigger 714404; Page et\nal., GCN #19967) simultaneously in g'r'i'z'JHK with GROND (Greiner\net al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the\nESO La Silla Observatory (Chile).\n\nObservations started at 02:48 UT on 2016-10-01, 1.71 hours\nafter the GRB trigger. They were performed at an average \nseeing of 2\" and at an average airmass of 2.3.\n\nWe found a faint singular point source which is south-west 2.2 arcsec \naway from the photometric center of nearby bright DSS2 object\nfor which Kruehler et al. (GCN #19971) reported X-Shooter spectroscopy.\nThe position is within the 2.3\" Swift-XRT error circle reported by \nEvans et al. (GCN #19968) and also within the 1.9\" enhanced XRT position \n(Osborne et al., GCN 19969), at\nRA (J2000.0) = 04 h 47 m 40.57 s   \nDEC (J2000.0) = -57d 15' 39.2\nwith an uncertainty of 0.5\" in each coordinate.\n\nBased on images with 36 min of total exposure in g'r'i'z'\nand 30 min in JHK at a mid-time of 03:58 UT on 2016-10-01,\nwe derive the following preliminary magnitudes and upper limits\n(all in the AB system):\n\ng' = 23.1 +- 0.2 mag,\nr' = 22.5 +- 0.1 mag,\ni' = 21.6 +- 0.1 mag,\nz' = 21.5 +- 0.1 mag,\nJ > 21.3 mag,\nH > 20.3 mag, and\nK > 18.7 mag.\n\nSecond-epoch observations were performed at a mean time \nof 09:19 UT at an average seeing 1.1\" and at an average airmass of 1.1.\nAt that time the source seems to have faded to:\n\nr' = 22.9 +- 0.1 mag\n\nGiven magnitudes are calibrated against USNO as well as 2MASS\nfield stars and are not corrected for the expected Galactic foreground\nextinction corresponding to a reddening of E_(B-V) = 0.01 mag in the\ndirection of the burst (Schlafly & Finkbeiner 2011).",
  "circularId": 19975,
  "createdOn": 1475344282000,
  "email": "jchen@mpe.mpg.de",
  "subject": "GRB 161001A: GROND afterglow candidate",
  "submitter": "Ting-Wan Chen at MPE  <jchen@mpe.mpg.de>",
  "eventId": "GRB 161001A"
}