{
  "bibcode": "2018GCN.22796....1S",
  "body": "T. Sakamoto (AGU), S. D. Barthelmy (GSFC),\nJ. R. Cummings (CPI), H. A. Krimm (NSF/USRA),\nS. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),\nC. B. Markwardt (GSFC), J. P. Norris (BSU),\nD. M. Palmer (LANL), M. Stamatikos (OSU),\nT. N. Ukwatta (LANL) (i.e. the Swift-BAT team):\n\nUsing the data set from T-239 to T+963 sec from the recent telemetry downlink,\nwe report further analysis of BAT GRB 180618A (trigger #842475)\n(LaPorte et al., GCN Circ. 22790).  The BAT ground-calculated position is\nRA, Dec = 169.948, 73.825 deg which is\n  RA(J2000)  =  11h 19m 47.6s\n  Dec(J2000) = +73d 49' 29.3\"\nwith an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).\nThe partial coding was 70%.\n\nThe mask-weighted light curve shows a short multi-peaked structure from ~ T0\nto ~T+0.3, followed by some extended emission that lasts till ~T+50 s.\nT90 (15-350 keV) is 47.4 +- 11.1 sec (estimated error including systematics).\n\nThe time-averaged spectrum from T-0.06 to T+56.33 sec is best fit by a simple\npower-law model.  The power law index of the time-averaged spectrum is\n1.39 +- 0.27.  The fluence in the 15-150 keV band is 6.7 +- 1.0 x 10^-7 erg/cm2.\nThe 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band\nis 2.2 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence\nlevel.\n\nThe structure of the burst shows similarity to those of short GRBs with\nextended emission, as mentioned in Hamburg et al., GCN Circ. 22794.\nWe thus perform further analysis on the short spike and the extended emission.\n\nThe spectrum of the short multi-peaked structure from T-0.056 to T+0.264 sec\nis best fit by a simple power-law model, with power-law index of 0.60 +- 0.24\nand fluence (15-150 keV) of 1.3 +- 0.2 x 10^-7 erg/cm2. The spectrum of the\nextended emission from T+0.264 to T+56.328 sec is best fit by a simple power-law\nmodel, with power-law index of 1.53 +- 0.31 and fluence (15-150 keV) of\n5.5 +- 1.0 x 10^-7 erg/cm2. These values are consistent with those of short GRBs\nwith extended emission (Lien & Sakamoto et al. 2016).\n\nUsing a 4-ms binned light curve, the lag analysis of the first two tallest pulses\n(from ~T0 to ~T+0.1 s) finds a lag of 0.7 +/- 0.9 ms for the 100-350 keV to 25-50 keV\nband, and 1.5 (+1.8, -1.2) ms for the 50-100 keV to 15-25 keV band. Therefore, the\nlag values of these short pulses are consistent with those of short GRBs.\n\nThe results of the batgrbproduct analysis are available at\nhttp://gcn.gsfc.nasa.gov/notices_s/842475/BA/",
  "circularId": 22796,
  "createdOn": 1529346443000,
  "email": "amy.y.lien@nasa.gov",
  "subject": "GRB 180618A: Swift-BAT refined analysis (a short GRB with extended emission)",
  "submitter": "Amy Lien at GSFC  <amy.y.lien@nasa.gov>",
  "eventId": "GRB 180618A"
}