GCN Circular 8758

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


We have analysed the first 35 ks of XRT observations for GRB 081230
(La Parola et al. GCN Circ 8753), with an exposure time of 104 s in WT mode and
11.4 ks in PC mode. The astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources to
the USNO-B1 catalogue) is RA, Dec = 37.3314 -25.1477, corresponding to:

RA (J2000): 02h 29m 19.53s
Dec (J2000): -25d 08' 51.8


with an uncertainty of 1.8 arcsec (radius, 90% confidence, Osborne et al.
GCN Circ 8756).

The lightcurve can be fitted with a broken power-law with the following
parameters:
alpha1=-6.910+/-0.007
T_break=298+/-9
alpha2=-0.62+/-0.5
There is evidence for a late flare a peaking at 5000s.

The spectrum of the data collected in WT mode can be fitted with a powerlaw
with photon index Gamma = 1.96 +/- 0.11, absorbed by the Galactic column in
this direction of 1.7x10^20 cm^-2, plus an intrinsic column of
(6.4+/-2.2)x10^20 cm^-2. The observed (unabsorbed) flux over this time
is 1.03x10^-9 (1.3x10^-9) erg cm^-2 s^-1,
corresponding to a counts to observed flux conversion of 4.1x10^-11 erg
cm^-2 count^-1.
The spectrum of the data collected in PC mode can be fitted with a powerlaw
with photon index Gamma = 2.14 (+0.10,-0.20), with an intrinsic column of
(5.3 [+2.2,-3.7])x10^20 cm^-2. The observed (unabsorbed) flux over this time
is 2.1x10^-12 (2.7x10^-9) erg cm^-2 s^-1,

With the present decay law, the count rate at 24 hours is predicted to be
1.1x10^-2 c/s (corresponding to an observed flux of 3.7x10^-13 erg cm^-2 s^-1)

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




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