GCN Circular 8609

V. La Parola, B. Sbarufatti, V. Mangano (INAF-IASF Pa), A. Parsons (GSFC)
report on behalf of the Swift XRT team:

We have analysed the first 3 orbits of Swift-XRT data obtained for
GRB 081203A (trigger #336489, Parsons et al., GCN Circ.8595
Not found
 
 
), that includes
550 s of Windowed Timing (WT) and 15.5 ks of Photon Counting (PC) mode data,
respectively, between 87 s and 16 ks after the trigger.
The UVOT-enhanced XRT position was given by Evans et al. in GCN Circ 8598.

The light-curve can be modelled with a broken power-law, with a steep
decay  alpha_1=4.32 � 0.16 and a break time at T_b=T0+(150+/-3) s.
After the break the decay flattens to alpha_2=1.175 � 0.015

The spectrum extracted from the WT data has an exposure of 558 s. It can be
modelled with an absorbed power-law, with Gamma =1.97 � 0.04 and an
intrinsic
NH = (5.5 � 0.8)x10^20 cm-2, in excess to the Galactic value of
1.7x10^20 cm-2.
The observed (unabsorbed) 0.3 -10 keV averaged flux over this time
interval is 8.6x10^-10 (10x10^-10) erg cm-2 s-1.

The spectrum extracted from the PC data in the time interval 0.6-16 ks
(with an
exposure time of 4.7 ks) can be modelled with an absorbed power-law, with
Gamma = 2.1 � 0.08 and an intrinsic column density of NH = (6.0 �
1.7)x10^20 cm-2.
The observed (unabsorbed) 0.3 -10 keV averaged flux over this time
interval is 2.8x10^-11 (3.6x10^-11) erg cm-2 s-1.
Uncertainties are given at 90% confidence.

If the light-curve continues to decay with the present rate, the count
rate 24
(36) hours after the burst is estimated to be 0.02 (0.013) count s-1, which
corresponds to an observed flux of 7x10^-13 (4.5x10^-13) erg cm-2 s-1.

The results of the xrt automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00336489.

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