[vsnet-grb-info 2424] GRB051111: XRT preliminary analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4261
SUBJECT: GRB051111: XRT preliminary analysis
DATE:    05/11/11 15:11:58 GMT
FROM:    Valentina La Parola at IASF-CNR sez. Palermo  <laparola at pa.iasf.cnr.it>

GRB051111: XRT preliminary analysis

V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA), T. Mineo
(INAF-IASFPA), G. Cusumano (INAF-IASFPA), D. N. Burrows (PSU), F.
Marshall (GSFC), A. Smale (NASA HQ), K. Page (U. Leicester) on behalf of 
the Swift/XRT team:

We have analysed 4 ks of XRT observations of GRB051111
(Sakamoto et al., GCN 4248). A bright source is well detected.
The refined coordinates for this X-ray afterglow are:

RA(J2000):   23h 12m 33.362s
Dec(J2000):  18d 22' 29.535"

with an estimated uncertainty of 3.5 arcsec (90% containment) and
including the latest XRT boresight correction.
The position is 71 arcsec from the on-board BAT position reported by
Sakamoto et al. and 2.4 arcsec from the optical afterglow first
detected by ROTSE (Rujopakarn  et al., GCN 4247).

The X-ray light-curve is steeply fading with a slope of -1.9+/-0.2.

The spectrum of the PC data can be modelled with an absorbed power-law
with photon index Gamma = 2.2+/-0.3 (90% containment).
There is a slight evidence for an absorbing column higher than the
Galactic value
(5.02e20 cm^-2) at a level of (9+/-5)e21 cm^-2 at the observed redshift
z=1.55 (Hill et al., GCN 4255).

The 0.2-10 keV unabsorbed flux at 5000 s  is 1.8e-11 erg cm^-2 s^-1.
At 10000 s the afterglow had faded to flux level of 5.0e-12 erg cm^-2
s^-1.
The predicted flux at T+24h is 8.8e-14erg cm^-2 s^-1