{
  "bibcode": "2015GCN.17757....1K",
  "body": "D. A. Kann (TLS Tautenburg), M. Tanga, and J. Greiner (both MPE Garching)\nreport on behalf of the GROND team:\n\nWe observed the field of the extremely bright short GRB 150424A (Swift\ntrigger 638946; Beardmore et al., GCN #17743) simultaneously in\ng'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the\n2.2 m MPG telescope at ESO La Silla Observatory (Chile).\n\nObservations started at 23:09 UT on 2015-04-24, 15.4 hrs after the GRB\ntrigger. They were performed at an average seeing of 1\".2 and at an\naverage airmass of 1.1.\n\nWe detect the optical afterglow (Perley & McConnell, GCN # 17745; Malesani\net al., GCN # 17756).\n\nBased on 7.7 min of total exposure time in g'r'i'z' and 8.0 min in JHK,\ncentered 15.54 hrs after the GRB, we estimate the following preliminary\nmagnitudes (all in AB system):\n\ng' = 22.0 +/- 0.2 mag,\nr' = 21.6 +/- 0.1 mag,\ni' = 21.4 +/- 0.1 mag,\nz' = 21.1 +/- 0.1 mag,\nJ  = 20.4 +/- 0.5 mag, and\nH  > 19.9  mag.\n\nCompared to the NOT detection about two hours earlier, the afterglow has\nfaded by 0.7 magnitudes, indicating the transition to a very rapid decay.\n\nGiven magnitudes are calibrated against GROND zero points (g'r'i'z') as\nwell as 2MASS field stars and are not corrected for the expected Galactic\nforeground extinction corresponding to a reddening of E_(B-V)=0.06 mag in\nthe direction of the burst (Schlegel et al. 1998).",
  "circularId": 17757,
  "createdOn": 1429919722000,
  "email": "kann@tls-tautenburg.de",
  "subject": "GRB 150424A: GROND detects strong fading",
  "submitter": "Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>",
  "eventId": "GRB 150424A"
}