{
  "bibcode": "2007GCN..6850....1P",
  "body": "D. A. Perley, R. Chornock, J. S. Bloom (UC Berkeley), C. Fassnacht, and \nM. W. Auger (UC Davis) report on behalf of GRAASP:\n\nWe obtained spectroscopic follow-up of the bright transient associated \nwith GRB 071003 (Schady et al., GCN 6837; Li, GCN 6838) starting at \n07:51 UT on the night of 2007-10-04 using Keck I + LRIS (range 3300-8630 \nAngstroms).  Two 10-minute exposures were acquired.\n\nThe source is well-detected and a preliminary reduction reveals a smooth \nspectrum consistent with a GRB afterglow with multiple absorption-line \nsystems.  We identify a pair of absorption features at 5870 and 5886 \nAngstroms with the Mg II 2796, 2803 Angstrom doublet at a redshift of \n1.100.  Other absorption features are consistent with Fe II 2382, 2586, \nand 2599 Angstroms at this redshift.  This absorption system sets a \nlower limit on the redshift of the GRB of z=1.100.\n\nIn addition, numerous lines (e.g., Mg II 2796, 2803 Angstroms, Mg I 2852 \nAngstroms, and Fe II 2599 Angstroms) are present from an intervening \nabsorption system at z=0.372.\n\nNo strong supernova features or host-galaxy emission lines are seen in \nthe spectrum.\n\nThis suggests that the transient is a GRB afterglow undergoing a bright \nlate-time optical flare, similar to the afterglow of GRB 070311 (e.g. \nHalpern & Armstrong, GCN 6203; Guidorzi et al., astroph/0708.1383), \nrather than a supernova.  That flare peaked at R~22 approximately two \ndays after the burst. Improved photometry of the optical transient \nassociated with GRB 071003 gives a magnitude of R = 19.1 +/- 0.3 at \n04:49 UT (0.88 days after the trigger) and further rebrightening appears \npossible. Further monitoring is strongly encouraged.",
  "circularId": 6850,
  "createdOn": 1191503484000,
  "email": "dperley@astro.berkeley.edu",
  "subject": "GRB 071003: Keck spectroscopy",
  "submitter": "Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>",
  "eventId": "GRB 071003"
}