[vsnet-grb-info 2450] GRB051117A : XRT refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4287
SUBJECT: GRB051117A : XRT refined analysis
DATE:    05/11/17 19:32:08 GMT
FROM:    Michael Goad at U Leicester  <mrg at star.le.ac.uk>

M. Goad, K. Page, D. Burrows (PSU), K. Hurley, (Berkeley), M. Chester (PSU)
report on behalf of the Swift XRT team.

>From analysis of 2.3 ks of Photon Counting mode data of GRB051117A (Band et
al., GCN 4280) we obtain a refined XRT position of RA: 15h 13m 33.8s, Dec:+30d
52m 13.3s (J2000) with an uncertainty of 3.4 arcsec (90% containment). This
includes the latest XRT boresight correction. This refined position is 41
arcsec from the BAT on-board position and 3.4 arcsec from the UVOT position
quoted in GCN 4280.

We have also analysed 1.77 ks of XRT Windowed Timing mode observations
starting 113 s after the BAT trigger. The XRT lightcurve displays multiple
flares with a peak count rate of approximately 180 ct/s occurring 134 s after
the BAT trigger. The early underlying decay slope of the XRT lightcurve is a
powerlaw with slope ~1.1+/-0.1.

The XRT WT mode 0.2-10 keV spectrum is well represented by an absorbed
powerlaw with photon index 2.23+/-0.02 with a mean unabsorbed flux of 2.6E-09
ergs/cm2/s (between 113 s and 5.2 ks after the burst). We find evidence for
excess NH above the Galactic value of 2.0e21 cm^-2.