{
  "bibcode": "2015GCN.17513....1T",
  "body": "M. Tanga, C. Delvaux, J. Greiner (all MPE Garching) and D. A. Kann (TLS\nTautenburg) report on behalf of the GROND team:\n\nWe observed the field of GRB 150301A (Swift trigger 632995; Lien et al.,\nGCN #17510) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,\nPASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla\nObservatory (Chile).\n\nObservations started at 06:02 UT on 01-03-2015, 4.97 hrs after the GRB\ntrigger. They were performed at an average seeing of 1.4\" and at an\naverage airmass of 1.5.\n\nWe found two point sources within the 5.0\" Swift-XRT error circle reported\nby Lien et al. (GCN #17510). The first source is at\n\nRA (J2000.0) = 16 h 17 m 13.08 s\nDEC (J2000.0) = -48d 42' 45.7\"\n\nThe second source is at\n\nRA (J2000.0) = 16 h 17 m 13.34 s\nDEC (J2000.0) = -48d 42' 49.7\"�\n\nwith an uncertainty of 0.3\" in each coordinate for both sources.\n\nBased on the first 50 min of total exposures in g'r'i'z' and 40 min in\nJHK, we estimate the following preliminary magnitudes (all in AB system):\n\nFor the first source:\n\ng' > 24.4 mag,\nr' > 24.5 mag,\ni' = 22.0 +/- 0.1 mag,\nz' = 21.0 +/- 0.3 mag,\nJ = 18.8 +/- 0.2 mag,\nH = 18.3 +/- 0.2 mag, and\nK > 18.3 mag.\n\nFor the second source:\n\ng' > 24.4 mag,\nr' > 24.5 mag,\ni' = 23.1 +/- 0.1 mag,\nz' = 22.2 +/- 0.1 mag,\nJ = 19.6 +/- 0.3 mag,\nH = 19.1 +/- 0.4 mag, and\nK > 18.3 mag.\n\nBoth objects appear to be constant over the duration of our observation.\nTherefore we suppose they are not related to the burst.\n\nWe note the field is crowded. We also notice the presence of a bright star\n(~14 mag) west of the Swift-XRT error circle covering around 10% of the\nencircled region.\n\nGiven magnitudes are calibrated against GROND zeropoints as well as 2MASS\nfield stars and are not corrected for the expected Galactic foreground\nextinction corresponding to a reddening of E_(B-V)=3.31 mag in the\ndirection of the burst (Schlafly & Finkbeiner 2011).",
  "circularId": 17513,
  "createdOn": 1425220195000,
  "email": "delvaux@mpe.mpg.de",
  "subject": "GRB 150301A: GROND Observations",
  "submitter": "Corentin Delvaux at MPE  <delvaux@mpe.mpg.de>",
  "eventId": "GRB 150301A"
}