GCN Circular 5746

A. Moretti (INAF-OAB), C. Guidorzi (Univ. Bicocca & INAF-OAB),
P. Romano (INAF-OAB) S. Campana (INAF-OAB) report on behalf of
the Swift-XRT team:

We have analysed the first 3 orbits of Swift-XRT data obtained for GRB
061021 (trigger=234905, GCN 5743
Not found
 
 
). The data consist of 189 s in Windowed
Timing (WT) mode, starting 78 seconds after the BAT trigger and 5.5 ks
in Photon Counting (PC) mode. Using PC data we obtain a refined
position of:

RA(J2000) =  09h 40m 35.87s
Dec(J2000)= -21d 57' 07.2"

with an estimated uncertainty radius of 5 arcsec (90% containment).
This location is 3.8 arcseconds from the UVOT position (GCN 5745
Not found
 
 
).

The light-curve, initially, shows a steep decay (alpha1=2.1+/-0.1) up
to a break at t_break=368+/-20.s.  After the break, the afterglow
shows a shallow decay (alpha2=0.55+/-0.03) up to the end of the third
orbit (t=12.5 ks). At this point the observed count rate was 2.2
counts per second, corresponding to an unabsorbed flux of 1.4E-11
erg/cm2/sec.

The spectrum formed from all the WT data can be modelled with a
power-law of photon index Gamma = 1.88 +/- 0.07, with an absorbing
column of NH = (3.4 +/- 0.8)E20 cm^-2 consistent with the Galactic
value of 4.20E20 cm^-2. The spectrum formed from the PC data is
slightly softer than the WT spectrum: it can be modelled with a
power-law of photon index Gamma = 1.96 +/- 0.08.
All errors are quoted at 90% confidence level.

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