{
  "bibcode": "2005GCN..3858....1C",
  "body": "J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC),\nD. Hullinger (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC),\nH. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),\nA. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS),\nJ. Tueller (GSFC)\non behalf of the Swift-BAT team:\n\nA second, larger, harder episode of gamma rays from T+217 to T+270\nsec was detected from GRB 050820A, as noted by Golenetskii et al. \nin GCN circ. 3846, 3852.  We confirm that this larger episode of \nemission was from the same source as the first episode (from T-17\nto T+22 sec), using BAT mask-weighting on a partial data set. \n\nSwift was entering the SAA as the first episode of emission was \nending.  We reported BAT refined analysis for the period covering \nthe first episode of emission in GCN circ. 3835, 3848.  The BAT \nentered SAA mode at T+241 sec.  At this time data collection became \nvery limited.  We use mask-weighted data prior to this time, and a \nnon-directional residual rate with a background model subtraction \nafter this time, for the following information on the second \nepisode:\n\nThere were two peaks at T+228 and T+259 sec.  T90 was 50 +/- 5 sec \n(for the second episode alone).  In a simple power law fit, the \nphoton index for the first part of the second episode from T+217 \nto T+241 was 1.06 +/- 0.03.  The 1-sec peak flux is estimated to \nbe 6 +/- 1 ph/cm^2/sec (15-350 keV) at T+259 sec.  For reference, \nthe previously reported photon index for the first episode of \nemission from T-17 to T+22 sec was 1.7 +/- 0.1 and the 1-sec peak \nflux was 1.3 +/- 0.2 ph/cm^2/sec (15-350 keV).  \n\nWe estimate the total fluence for the entire event including both \nepisodes to be 8.4 +/- 0.3 x 10^-6 erg/cm^2 in the 15-150 keV band.  \nThe quoted uncertainty is statistical. Roughly 60% of the fluence \nis in the period lacking mask-weighted data and having a very high\nbackground rate, thus systematic errors may be large and we \nestimate them to be +/- 0.6 x 10^-6 erg/cm^2.  The fluence estimate \nincludes the assumption that the part of the second episode after \nT+241 sec had the same spectrum as it did from T+217 to T+241 sec.\n\nFor the entire burst then, using the measured redshift of 2.612 \n(Prochaska, et al. GCN 3833), we calculate the isotropic-equivalent \nenergy in the 54-542 keV band in the GRB rest frame (15-150 keV \nband in the observer's frame) as ~1.5 x 10^53 ergs.\n-- \nJay Cummings",
  "circularId": 3858,
  "createdOn": 1124740541000,
  "email": "jayc@milkyway.gsfc.nasa.gov",
  "subject": "GRB 050820A BAT observations of second, larger episode of emission",
  "submitter": "Jay R. Cummings at NASA/GSFC/Swift  <jayc@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 050820A"
}