[vsnet-grb-info 3945] GRB061028: XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5767
SUBJECT: GRB061028: XRT refined analysis
DATE:    06/10/28 14:25:10 GMT
FROM:    Teresa Mineo at INAF-IASFA  <teresa.mineo at ifc.inaf.it>

G. Cusumano (IASF-Pa INAF), T. Mineo (IASF-Pa INAF), V. Mangano (IASF-Pa 
INAF),
B. Sbarufatti (IASF-Pa INAF) and T. Sakamoto (GSFC/ORAU)
report on behalf of the Swift XRT team:

We have analyzed the first 4 orbits of Swift-XRT data obtained for GRB
061028 (trigger=235715, GCN 5762). The data consist of 100 s in Windowed
Timing (WT) mode, starting 205 seconds after the BAT trigger and 8 ks
in Photon Counting (PC) mode.

Using PC data we obtain a refined position of:

RA(J2000) =  06h 28m 54.53s
Dec(J2000)= +46d 17' 55.20"

with an estimated uncertainty radius of 3.9 arcsec (90% containment)
taking into account the new TELDEF files .  This location is 0.4 arcsec
from the first XRT position (GCN 5762).

The light-curve shows a steep decay (alpha=3.9±0.4) up to the  end of the
second orbit.  Data relative to the next two orbits show a detection at 3
sigma level with a count rate of  (3±1)E-3 corresponding to a flux of
1.5E-13 erg cm^-2 sec^-1, significantly higher than the model 
extrapolation.

The spectrum from all the WT data can be modeled with a
power law of photon index Gamma = 1.4 ± 0.1, with an absorbing
column of NH = (2.4±0.6)E21 cm^-2, significantly higher than the
Galactic value of 1.37E21 cm^-2. The 0.2-10 keV unabsorbed flux
during the WT is 5.7E-10 erg cm^-2 sec^-1. The spectrum from
the PC data is softer than the WT spectrum: it can be modeled with a
power-law of photon index Gamma = 2.4±0.4.
All errors are quoted at 90% confidence level.

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