{
  "bibcode": "2009GCN..9677....1G",
  "body": "C. Guidorzi (U. Ferrara), Z. Cano, A. Melandri, C.G. Mundell,\nR.J. Smith, I.A. Steele,  D. Bersier, S. Kobayashi (Liverpool JMU),\nA. Gomboc (U. Ljubljana) on behalf of a large collaboration report:\n\nWe began observing the Swift GRB 090715B (Vetere et al. GCN Circ. 9668)\nwith the Liverpool Telescope (LT) on July 15, 21:14:19 UT\n(11.0 min post BAT trigger) with the SDSS riz filters,\nconfirming the detection of the optical afterglow seen by\nSwift-UVOT (Smith et al. GCN Circ. 9670; Malesani et al GCN\nCirc. 9671; Antonelli et al. GCN Circ. 9675).\nObservations with the LT carried on until 5.6 hours post burst.\nOur measurements are in agreement with the value reported by\nMalesani et al. (GCN Circ. 9671) after correcting for the\ndifferent calibration.\n\nWe also observed the OT with the Faulkes Telescope North (FTN)\nfrom July 16, 09:45:46 UT (i.e., at 12.71 hours) with the R filter.\n\nThe light curve in the r filter from 0.18 to 12.7 hours can be\nfitted with a broken power-law with alpha1=0.25 +/- 0.02,\nt_break =18 (-3, +12) ks, alpha2~0.7.\n\n\nTelescope   Mid Time   Exposure  Filter   Mag\n            (hours)     (s)\n------------------------------------------------------\nFTN         12.90      1200        R     20.98 +- 0.05\n------------------------------------------------------\n\nCalibration was performed against the SDSS star mentioned\nby Malesani et al. (GCN 9671), assuming r'=17.74 and R=17.54.",
  "circularId": 9677,
  "createdOn": 1247744968000,
  "email": "guidorzi@fe.infn.it",
  "subject": "GRB 090715B: break in the optical afterglow decay",
  "submitter": "Cristiano Guidorzi at Ferrara U,Italy  <guidorzi@fe.infn.it>",
  "eventId": "GRB 090715B"
}