TITLE:   GCN CIRCULAR
NUMBER:  6955
SUBJECT: GRB 071020: Swift-XRT refined analysis
DATE:    07/10/20 19:03:38 GMT
FROM:    Andy Beardmore at U Leicester  <apb@star.le.ac.uk>

A.P. Beardmore, K.L. Page, P.A. Evans (U. Leicester) and S.T. Holland
(CRESST/USRA/GSFC) report on behalf of the Swift-XRT team:

The Swift-XRT began observing the BAT GRB 071020 (trigger #294835) at
07:03:28 UT, 61 seconds after the BAT trigger.  In a 1.23ks
exposure Photon Counting mode image obtained during the first orbit
we find a refined XRT position of RA, Dec (J2000) = 119.66521, 32.86079 
which is

RA(J2000)  =  07:58:39.65
Dec(J2000) = +32:51:38.8

with an estimated uncertainty of 4.0 arcsec (radius, 90 percent
containment).  This is 13.9 arcsec from the refined BAT position
(Tueller et al., GCN 6954), 4.1 arcsec from the position
of the ROTSE-IIIb afterglow (Schaefer et al., GCN 6948), and
2.3 arcsec from the PAIRITEL position (Bloom et al., GCN 6953).

Due to a high CCD operating temperature caused by the unfavourable sky
position of the burst, along with bright Earth activated hot-pixels,
the XRT remained in Windowed Timing mode for orbits 2 to 5 at which
point the initial Swift observations were halted for today. However,
using the XRT data available at these times, the 0.3-10.0keV X-ray
light curve from T+68s to T+17.6ks shows a powerlaw decline with a
decay index of 1.11+/0.02.

The Windowed Timing mode spectrum from the first orbit (T+68s to
T+315s) is well fit by an absorbed powerlaw with a photon index of
1.86+/-0.07 and a redshifted column density of (4.3+/-1.7)e21 cm^-2
(at z=2.145, Jakobsson et al., GCN 6952), in addition to the 5.1e20
cm^-2 galactic column density in this direction. The observed 0.3-10.0
keV flux during this time is (6.1+/-0.2)e-10 erg cm^-2 s^-1.

Assuming the X-ray light curve decays at the same rate we predict an
XRT count rate of 0.014 count s^-1 at T+24 hours, which corresponds to an
observed 0.3-10keV flux of 6.0e-13 erg cm^-2 s^-1.

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