{
  "bibcode": "2008GCN..7704....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), R. Chornock (UCB), B. Cobb (Yale), P. B. Hall\n(York U.), A. V. Filippenko (UCB), N. Gehrels (NASA/GSFC), D. Burrows (PSU),\nK. Glazebrook (Swinburne), J. Granot (U. Hertfordshire), K. C. Hurley (UCB),\nD. Kocevski (UCB), B. Metzger (UCB), M. Modjaz (UCB), A. Miller (UCB), W.\nLee (I. de Astronomia), S. Lopez (U. Chile), J. Norris (NASA/Ames), P. E.\nNugent (LBNL), M. Pettini (U. Cambridge), D. Poznanski (UCB), A. L. Piro\n(UCB), E. Quataert (UCB), E. Ramirez-Ruiz (UCSC), J. Shiode (UCB), and T.\nSakamoto (GSFC/UMBC) report:\n\nFrom 2008/05/07 19:18:23 UT to 2008/05/08 04:09:59 UT (4.29 - 4.66 days post\nburst), Chandra Director's Discretionary Time observations with ACIS-S were\nconducted of the field of GRB 080503 (Mao et al. 2008; GCN7665) for a\ntotal exposure of 29.8 ksec (livetime).  We find a highly significant\ndetection of one X-ray point source in the XRT error circle (Goad et al.\n2008; GCN7669) at:\n\nRA, Dec = 19:06:28.76, +68:47:35.3 +/- 0.5\"  (J2000).\n\nThe source is 0.2\" away from the Gemini optical source (S2) in Perley et al.\n(2008; GCN7678), and is 0.7\" away from the center of the XRT error circle.\nThe X-ray source is therefore highly likely to be associated with S2, which\nis in turn highly likely to be associated with GRB 080503.  Astrometry is\nestablished using Chandra field sources also detected in the Gemini images.\n\nWe detect 40+/-6 counts in the 0.5-8.0 keV band.  There is weak evidence\nin favor of variability.  During the first half of the exposure, we measure\n21+/-5 cts, as compared to 19+/-4 counts in the second half.  Testing\nagainst the NULL hypothesis of a steady source, we find KS-prob=0.23.\n\nThe Chandra flux implies a flattening of the X-ray flux relative to\nthe rapid decay observed prior to ~13 ksec by the Swift XRT (Guidorzi et al.\n2008; GCN7674).  We note also that XRT observations at late time (2.4-3.2\ndays post burst) exhibit a flux consistent with that of Chandra, yielding a\nmarginal (~1-sigma) XRT detection.\n\nMinimizing the Cash (1976) statistic, we find the Chandra spectrum to\nbe acceptably fit by an absorbed powerlaw with photon index Gamma=1.5+/-0.5\nand unabsorbed flux Fx(0.3-10 keV) = (1.5+/-0.7) x 10^(-14) erg/cm^2/s.  We\nassume Galactic absorption only, as observed for the Swift XRT spectrum\n(Guidorzi et al. 2008; GCN7674).\n\nRoughly, the X-ray flux is consistent with an extrapolation of the optical\nflux as observed by HST (Bloom et al. 2008; GCN7703), assuming the X-ray\nspectral index.  If the optical flux is due to a a Li-Paczynski\n\"mini\"-supernova (1998ApJ...507L..59L) as suggested by Perley et al. (2008;\nGCN7678), then the X-ray light curve may be more easily explained by\ninvoking a separate emission mechanism.  Alternatively, both the optical\nand X-ray fluxes may be due to shock energy re-injection or flaring \noccuring on timescales ~1-4 days post burst.\n\nMore detailed analyses are ongoing.\n\nWe thank Harvey Tananbaum, Patrick Slane, Andrea Prestwich, and the\nrest of the Chandra observatory staff for their impressive rapid scheduling\nand execution of this observation.\n\nThis message can be cited.",
  "circularId": 7704,
  "createdOn": 1210371527000,
  "email": "nrbutler@space.mit.edu",
  "subject": "GRB 080503: Chandra Observation of X-ray Rebrightening or Flattening",
  "submitter": "Nat Butler at MIT/CSR  <nrbutler@space.mit.edu>",
  "eventId": "GRB 080503"
}