{
  "bibcode": "2008GCN..7775....1B",
  "body": "N. R. Butler (UC Berkeley), J. S. Bloom (UCB), W. Li (UCB), A. J. Levan (U.\nWarwick), D. A. Perley (UCB),  N. R. Tanvir (U. Leicester), H-W. Chen (U.\nChicago), R. Chornock (UCB), J. X. Prochaska (UCO/Lick), C. D. Bailyn (Yale),\nA. Bunker (U. Exeter), B. Cobb (Yale), P. B. Hall (York U.), A. V. Filippenko\n(UCB), N. Gehrels (NASA/GSFC), D. Burrows (PSU), K. Glazebrook (Swinburne),\nJ. Granot (U. Hertfordshire), K. C. Hurley (UCB), D. Kocevski (UCB), B.\nMetzger (UCB), M. Modjaz (UCB), A. Miller (UCB), W.  Lee (I. de Astronomia),\nS. Lopez (U. Chile), J. Norris (NASA/Ames), P. E.  Nugent (LBNL), M. Pettini\n(U. Cambridge), D. Poznanski (UCB), A. L. Piro (UCB), E. Quataert (UCB), E.\nRamirez-Ruiz (UCSC), J. Shiode (UCB), and T.  Sakamoto (GSFC/UMBC) report:\n\nFrom 2008/05/25 18:11:36 UT to 2008/05/26 03:04:28 UT (22.24 - 22.61 days post\nburst), Chandra Director's Discretionary Time observations with ACIS-S were\nconducted of the field of GRB 080503 (e.g., Mao et al. 2008; GCN 7665) for a\ntotal exposure of 29.8 ksec (livetime).  In a 3-pixel radius source extraction\nregion centered around the first epoch Chandra source (Butler et al. 2008;\nGCN 7704), we find no source counts in the 0.5-8.0 keV band.\n\nWe derive a 2-sigma upper limit to the source flux of Fx(0.3-10 keV) < 9.9 x\n10^(-16) erg/cm^2/s.  Relative to the first epoch flux ~18 days earlier,\nthe 2nd epoch flux implies a fade steeper in time than t^(-1.6).  A similarly\nsteep or steeper fade is implied in the optical band from Gemini and HST\nobservations of this source (Perley et al. 2008; GCNs 7667, 7678, 7679, 7680,\n7695, 7703, 7749).  Combined with a rough agreement in the extrapolated flux\nlevels assuming a GRB afterglow external shock model (e.g., GCN 7704), the\nlightcurve similarity supports an interpretation where the external shock is\nresponsible for both the X-ray and optical emission.\n\nMore detailed analyses are ongoing.\n\nWe thank Harvey Tananbaum and the Chandra observatory staff for their\nimpressive rapid scheduling and execution of this observation.\n\nThis message can be cited.",
  "circularId": 7775,
  "createdOn": 1211845835000,
  "email": "nrbutler@space.mit.edu",
  "subject": "GRB 080503: 2nd Epoch Chandra X-ray Observations",
  "submitter": "Nat Butler at MIT/CSR  <nrbutler@space.mit.edu>",
  "eventId": "GRB 080503"
}