{
  "subject": "Swift-BAT/-XRT refined analysis on trigger 324362 (LS I +61 303)",
  "bibcode": "2008GCN..8215....1B",
  "createdOn": 1221158731000,
  "circularId": 8215,
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>",
  "email": "scott@lheamail.gsfc.nasa.gov",
  "body": "S. D. Barthelmy (GSFC), W. Baumgartner, J. Cummings (GSFC/UMBC),\nN. Gehrels (GSFC), C. Markwardt (GSFC/UMD), T. Sakamoto (GSFC/UMBC),\nO. Godet, P. Evans, J. Osborne, A. P. Beardmore (U Leicester),\nJ. Kennea, A.  Falcone, D. Burrows (PSU), S. Campana (INAF-OAB),\nM. De Pasquale (UCL-MSSL)\n(for the Swift-BAT and -XRT teams):\n \nUsing the data set from T-120 to T+182 sec from recent telemetry downlinks,\nwe report further analysis of BAT trigger #324362 (De Pasquale, et al.,\nGCN Circ. 8209).  The BAT ground-calculated position is\nRA, Dec = 40.101, 61.210 deg which is \n   RA(J2000)  =  02h 40m 24.3s \n   Dec(J2000) = +61d 12' 34.7\" \nwith an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).\nThis is 88 arcsec from the High Mass X-ray Binary source LS I +61 303 (=V615 Cas).\nThe partial coding was 100%.\n \nThe mask-weighted light curve shows a single peak with a rise slightly faster\nthan the decay.  It starts at T+0.0 and ends at T+0.360 sec.\nT90 (15-350 keV) is 0.23 +- 0.05 sec (estimated error including systematics).\n \nThe time-averaged spectrum from T+0.0 to T+0.3 sec is best fit by a black \nbody model.  This fit gives a temperature of kT = 7.5 +- 1.0 keV (chi squared \n52.9 for 57 d.o.f.).  For this model the total fluence in the 15-150 keV band \nis 1.6 +- 0.3 x 10^-08 erg/cm2 and the 1-sec peak flux measured from T-0.33 sec \nin the 15-150 keV band is 1.3 +- 0.2 ph/cm2/sec.  A fit to a simple power law \ngives a photon index of 2.44 +- 0.31 (chi squared 65.7 for 57 d.o.f.).  All the \nquoted errors are at the 90% confidence level.\n \nThe results of the batgrbproduct analysis are available at\nhttp://gcn.gsfc.nasa.gov/notices_s/324362/BA/\n\n\nWe have analysed the 12.7ks of Photon Counting (PC) data obtained for the BAT\ntrigger 324362 starting from 921.1s after the BAT trigger (T0) to T0+65ks.\nThe XRT detected, using promptly downlinked data, an X-ray source coincident\nwith the High Mass X-ray binary LS I +61 303 (Evans et al., GCN Circ. 8211).\n \nThe 0.3-10 keV X-ray light-curve shows an initial count rate of ~0.4 c/s up to\n~T0+10ks; the count rate then drops to a relatively steady level of \n0.1-0.2 c/s.\n\nThe spectrum from PC data (from T0+921s to T0+65ks) can be fitted by an\nabsorbed power-law with a column density of (5.9 +0.9/-0.8)e21 cm**-2 and a\nphoton index of 2.01 +0.14/-0.13 (chi^2/dof = 68/76). The 0.7-10 keV observed\n(unabsorbed) flux is (9.2 +0.6/-1.3)e-12 (1.3e-11) erg/cm**2/s.\n \n\nGiven (a) the soft gamma-ray spectrum (b) the spatial proximity to the\nLS I +61 303 source, and (c) the X-ray temporal variability and the spectral\nbehaviour are consistent with what was observed in past observations\nof the HMXB LS I+61 303, we believe this outburst to be from that source.\nHowever, we note that the BAT lightcurve is uncharacteristic for this type\nof source, so we can not rule out a GRB origin.  We also note that the softness\nof the spectrum puts this on the soft-side tail of the distribution for SHBs,\nand the gamma-ray duration is also on the short-side of that distribution\nfor SHBs.\n\n\nWe correct the statement in GCN Circ 8209 about \"Swift slewing immediately\nto the source\".  The slew was actually delayed for 14.7 minutes due to the\ntargets in the preplanned observing program having higher merit values."
}