TITLE:   GCN CIRCULAR
NUMBER:  5970
SUBJECT: GRB061222B: Swift-XRT Refined Analysis
DATE:    06/12/22 14:00:47 GMT
FROM:    Judith Racusin at PSU  <racusin@astro.psu.edu>

J. L. Racusin, J. Kennea (PSU), J. P. Osborne, and K. L. Page (U 
Leicester) report on behalf of the Swift XRT team:

We have analyzed the first two orbits of Swift-XRT data on GRB 061222B 
(Racusin et al. GCN 5957), with a total exposure of 119 seconds in Window 
Timing (WT) mode and 906 seconds in Photon Counting (PC) mode.  This 
provides a refined XRT position at RA, Dec = 105.35321, -25.8594 which is:

RA(J2000) = 7h 01m 24.77s
Dec(J2000) = -25d 51' 33.9"

with an estimated error radius of 3.7 arcseconds (90% confidence).  This 
position is 20 arcseconds from the initial BAT position (Racusin et al. 
GCN 5957), 1.8 arcseconds from the initial XRT position (Racusin et al. 
GCN 5957), and 3.1 arcseconds from the optical candidate discovered by 
Berger et al. (GCN 5956).

The 0.3-10 keV X-ray light curve between 145s and 4900s after the trigger 
can be fit with a broken power-law with an initial decay slope of 3.26 +/- 
0.10, a break at 450s, and a post-break slope of 1.24 +/- 0.15.

The X-ray spectrum from the WT data covering the time period from T+145s 
to T+264s is well fit by an absorbed power-law with a photon index of 2.6 
+/- 0.2 and column density of (4.0 +/-0.6 )e21 cm**-2. We note the 
Galactic column density in the direction of the source is 2.7e20 cm**-2. 
The unabsorbed 0.3-10 keV flux for this spectrum is 8.7e-10 erg/cm**2/s.

Assuming the X-ray emission continues to decline at the same rate, we 
predict a 0.3-10 keV XRT count rate of 1e-3 count/s at T+24hr, which 
corresponds to an observed 0.3-10 keV flux of 3.6e-14 erg/cm**2/s.

After the initial first orbit and partial second orbit of automated 
observations, the automated target was changed back to GRB061222A due to 
XRT thermal constraints.  Observations of GRB061222B will continue at a 
later time.

This circular is an official product of the Swift XRT Team.