[vsnet-grb-info 4411] GRB 070311: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6192
SUBJECT: GRB 070311: Swift-XRT refined analysis
DATE:    07/03/11 12:41:53 GMT
FROM:    Cristiano Guidorzi at INAF-OAB  <cristiano.guidorzi at brera.inaf.it>

C. Guidorzi, P. Romano, S. Vergani and A. Moretti (Uni-Bicocca and OAB)
report on behalf of the Swift-XRT team:

We have analysed the first two orbits of Swift-XRT data obtained for the
GRB 070311 detected by INTEGRAL (Mereghetti et al., GCN Circ. 6189),
which includes 4.2 ks of Photon Counting (PC) mode data, beginning
7000 s after the burst trigger time.
Using the PC data we found a fading source at the position of
RA, Dec = 87.5351, 3.3750, which is equivalent to

RA(J2000)  =  05 50 08.43
Dec(J2000) = +03 22 30.0

with an estimated error radius of 3.8 arcsec (90% confidence). This lies
3.3 arcsec from the optical afterglow discovered by REM (Covino et al.,
GCN Circ. 6190) and confirmed by PAIRITEL (Bloom et al., GCN Circ. 6191).

The XRT light-curve can be fit with a single power law with index of
1.9 ± 0.4 from 7 ks to 14 ks after the burst.

The PC photon spectrum can be modelled by a power-law of Gamma=1.6 +/- 0.2,
with a total absorbing column fixed to the Galactic value of 2.6x10^^21 
cm^-2
in this direction. Alternatively, if the absorbing column is left free 
to vary,
we find Gamma=1.9 +/- 0.4 and a column density of (3.8 +/- 1.6)x1021 cm^-2
(90% confidence).

The mean observed (unabsorbed) flux over 0.3-10 keV over this period
is 3.9e-12 (4.9e-12) erg cm^-2 s^-1.

If the decay continues with the same rate as above, the count rate is
predicted to be 1.1e-3 count s^-1 at 24 hours. This corresponds to an
observed flux of 6.5e-14 erg cm^-2 s^-1 (over 0.3-10 keV), with the
unabsorbed value being 7.9e-14 erg cm^-2 s^-1, using the spectral fit to
the PC data.

This circular is an official product of the XRT team.