[vsnet-grb-info 2625] GRB 060109: Refined Swift-XRT analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4462
SUBJECT: GRB 060109: Refined Swift-XRT analysis
DATE:    06/01/10 08:15:16 GMT
FROM:    Kim Page at U.of Leicester  <kpa at star.le.ac.uk>

A.P. Beardmore, K.L. Page (U.Leicester), J. Kennea (PSU), M. De Pasquale
(UCL-MSSL), P. Meszaros, M. Chester (PSU) report on behalf of the Swift
XRT team:

We have analysed the first four orbits of Swift-XRT data from GRB 060109.
8.3ks of PC mode data give a refined position of

RA(J2000)   =  18h 50m 43.5s
Dec(J2000)  = +31d 59' 29.7"

with an estimated uncertainty of 3.2 arcsec (90% containment). This
position is 7.7 arcsec away from the on-board XRT position quoted in De
Pasquale et al. (GCN 4455) and includes the latest XRT boresight
correction.

The X-ray lightcurve shows a steeply declining early phase, with a decay
slope of 5.1, which breaks to a shallower slope of 0.14 at about 300s.  
This is followed by a second break at 6100s to a slope of 1.2.

The X-ray spectrum 100s to 200s after the BAT trigger can be fitted with
an absorbed power-law with a photon index of 1.85+/-0.09 and a column
density consistent with the Galactic value in this direction of 1.0e21
cm**2.  The observed (unabsorbed) 0.3-10.0 keV flux over this interval is
5.1E-10 (6.2E-10) ergs cm**-2 s**-1.

If the source continues to fade at the current rate we predict an XRT
count rate of 0.006 counts/s 24hrs after the trigger, which corresponds
to an observed (0.3-10 keV) flux of 2.4e-11 ergs cm**-2 s**-1.