[vsnet-grb-info 5454] GRB 071122 Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7126
SUBJECT: GRB 071122 Swift-XRT refined analysis
DATE:    07/11/22 10:23:32 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

P.A. Evans, K.L. Page, R.L.C. Starling (U. Leicester) and M. Stamatikos
(NASA/ORAU) report on behalf of the Swift-XRT team:

We have analysed 1.4 ks of Swift XRT data for GRB 071122 (Stamatikos et
al. GCN Circ 7121), comprising 125 s in Windowed Timing (WT) mode and
1.3 ks in Photon Counting (PC) mode. The observations started 146 s
after the BAT trigger. Using 778 s of overlapping XRT Photon Counting
mode and UVOT V-band data, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 276.60547, 47.07504 which is
equivalent to:

RA (J2000):  18 26 25.31
Dec (J2000): +47 04 30.1

with an uncertainty of 1.7 arcsec (radius, 90% confidence). This
position is 1.5 arcsec from the optical afterglow reported by Cenko (GCN
Circ 7125), 74 arcsec from the initial BAT position, within the BAT
error circle, and 7.1 arcsec from the initial XRT position.

The XRT light curve follows a power-law decay with alpha=2.52
(+0.10/-0.09). There is also a small flare at approximately T0+400 s.

The WT mode spectrum can be fitted with an absorbed power-law, with the
absorption column fixed at the Galactic value of 4.75e20 cm^-2. Adding a
redshifted absorber at z=1.14 (Cucchiara et al. GCN Circ 7124) improved
the fit marginally, with chi-squared decreasing from 36.14 for 39
degrees of freedom, to 32.83 for 38 degrees of freedom. An f-test
indicates that the probability of this being a chance improvement is
~5%. The redshifted absorber has a column density of 9.9e20
(+10.0e20/-9.0e20) cm^-2, and a power-law index, gamma of 2.00
(+0.14/-0.13). The observed (unabsorbed) 0.3-10 keV flux is 2.52e-10
(3.04e-10) erg cm^-2 s^-1.

The predicted count-rate at T+24 hours is 1.69e-6 s^-1, which
corresponds to an observed (unabsorbed) 0.3-10 keV flux of 6.11e-17
(7.37e-17) erg cm^-2 s^-1.

Due to the proximity of this GRB to the sun, no further observations are
planned.

This circular is an official product of the Swift-XRT team.