{
  "bibcode": "2016GCN.19148....1U",
  "body": "T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester),\nJ. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),\nA. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), J. P. Norris (BSU),\nD. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU)\n(i.e. the Swift-BAT team):\n\nUsing the data set from T-61 to T+200 sec from the recent telemetry downlink,\nwe report further analysis of BAT GRB 160303A (trigger #677495)\n(Beardmore, et al. GCN Circ. 19126).  The BAT ground-calculated position is\nRA, Dec = 168.710, 22.710 deg which is\n  RA(J2000)  =  11h 14m 50.3s\n  Dec(J2000) = +22d 42' 35.1\"\nwith an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).\nThe partial coding was 96%.\n\nThe mask-weighted light curve shows a short spike that start and peaks at ~T0,\nand ends at ~T+0.4 s. There is a hint of a weak tail that lasts till ~T+5 s\nT90 (15-350 keV) is 5.0 +- 0.8 sec (estimated error including systematics).\n\nNote that for this burst, the auto process generates fairly inconsistent results of the\nburst durations (ranging from T90 of ~ 0.4 s to T90 of ~ 18 s) when using light curves\nwith different time bins and/or different length of data range. This is likely due to the\nambiguous weak-tail feature in the light curve after the short spike.\n\nThus, we did further checks of the reality of the weak tail by an alternative Bayesian\nBlock method based on Scargle et al. (2013), and by searching for detections in\nimages created using different time intervals. We conclude that there is likely no burst\nemission after ~T+5 s, because no burst structure is picked out by the alternative\nBayesian Block method afterwards, and also the signal-to-noise ratio is only about\none in images created after ~T+5. The image created using T+1 s to T+5 s gives\na signal-to-noise ratio of ~ 4.\n\nThe lag analysis using the 8-ms binned light curve shows a lag of 24 ms +- 24 ms\nfor the 100-350 keV to 25-50 keV band, which is inconclusive for the burst nature\ndue to the weakness of the burst.\n\nWe therefore decided to report T90 based on results using data till ~T0+200 s,\nwhich gives a T90 of ~ 5 s and is consistent with our checks. However, due to\nthe relatively low significance of the tail. We report the spectral analyses for\nboth the total range and the the short spike.\n\nThe time-averaged spectrum from T-0.1 to T+5.3 sec is best fit by a simple\npower-law model.  The power law index of the time-averaged spectrum is\n1.01 +- 0.33.  The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-7 erg/cm2.\nThe 1-sec peak photon flux measured from T-0.09 sec in the 15-150 keV band\nis 1.0 +- 0.1 ph/cm2/sec.\n\nThe spectrum of the short spike from T-0.09 to T+0.40 sec is best fit by a simple\npower-law model.  The power law index of the short-spike spectrum is\n0.84 +- 0.20.  The fluence in the 15-150 keV band is 8.78 +- 1.1 x 10^-8 erg/cm2.\nAll the quoted errors are at the 90% confidence level.\n\nThe results of the batgrbproduct analysis are available at\nhttp://gcn.gsfc.nasa.gov/notices_s/677495/BA/",
  "circularId": 19148,
  "createdOn": 1457132216000,
  "email": "amy.y.lien@nasa.gov",
  "subject": "GRB 160303A, Swift-BAT refined analysis",
  "submitter": "Amy Lien at GSFC  <amy.y.lien@nasa.gov>",
  "eventId": "GRB 160303A"
}