{
  "bibcode": "2009GCN..9699....1C",
  "body": "A. Cucchiara (PSU), S. B. Cenko (UC Berkeley), D. B. Fox (PSU),\nE. Ofek (Caltech), N. Tanvir (U. Leicester) report:\n\n\"On April 21.26 UT and 22.24 UT we obtained two R-band images\nof the Fermi/Swift GRB 090720 (GCN 9688,  9694) with GMOS on\nthe Gemini-North telescope for a total exposure time, at each\nepoch, of 15 minutes.\n\nIn the coadded images we identify a possible R counterpart inside\nthe XRT error circle (Grupe et al., GCN 9697) at the coordinates:\n\nRA (J2000): 13:34:43.33\nDec (J2000): -10:20:04.9\n\nwith an uncertainty of 0.5\".\n\nThe estimated magnitude at the two epochs are:\n\nR = 21.50 +- 0.03 mag\nR = 22.34 +- 0.04 mag\n\nThe implied fading, by 0.84 +- 0.05 mag between our two epochs,\nis consistent with a power-law decay of index alpha=1.12 +- 0.11\nreferenced to the burst trigger time.\nWe conclude from this fading behavior that the source is the optical\nafterglow of GRB 090720.\n\nMagnitude values are calibrated using the USNO B1 star at\n\nRA= 13:34:39.9\nDec= -10:20:17.06\n\nwhich has tabulated magnitude R = 19.79.\nWe thank the Gemini-N staff for the support in performing this\nobservations, in particular Tom Geballe and Paul Hirst.\"",
  "circularId": 9699,
  "createdOn": 1248278414000,
  "email": "cucchiara@astro.psu.edu",
  "subject": "GRB 090720:  Gemini-North Imaging and Optical Afterglow",
  "submitter": "Antonino Cucchiara at PSU  <cucchiara@astro.psu.edu>",
  "eventId": "GRB 090720"
}