TITLE:   GCN CIRCULAR
NUMBER:  14263
SUBJECT: GRB 130305A: Swift/XRT detection of the afterglow
DATE:    13/03/06 15:50:04 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>

Daniele Malesani (DARK/NBI), Bin-Bin Zhang (PSU), David N. Burrows 
(PSU), Dirk Grupe (PSU), report on behalf of the Swift-XRT team:

The Swift spacecraft observed the ground-discovered BAT GRB 130305A 
(Cummings & Palmer, GCN 14257), also detected by Fermi GBM and LAT (Yu & 
Xiong, GCN 14261; Guiriec et al., GCN 14260), Konus/Wind (Golenetskii et 
al., GCN 14262) and INTEGRAL SPI-ACS.

We have analysed 1.8 ks of XRT data, from 31.0 ks to 47.2 ks after the 
Swift/BAT trigger. The data are entirely in photon counting (PC) mode. 
An X-ray source is detected within the Swift/BAT error circle. The XRT 
position is RA, Dec = 116.74762, +52.03332 which is equivalent to:

RA (J2000) = 07 46 59.43
Dec(J2000) = +52 01 60.0

with an uncertainty of 3.8 arcsec (radius, 90% confidence). This 
position is 49 arcsec from the Swift/BAT position.

A spectrum formed from the PC mode data can be fitted with an absorbed 
power-law with a photon spectral index of 2.0 (+0.7, -0.6). The 
best-fitting absorption column is  4.1 (+3.6, -2.5) x 10^21 cm^-2, in 
excess of the Galactic value of 4.8 x 10^20 cm^-2 (Kalberla et al. 
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion 
factor deduced from this spectrum  is 4.3 x 10^-11 (7.3 x 10^-11) erg 
cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:         4.1 (+3.6, -2.5) x 10^21 cm^-2
Galactic foreground: 4.8 x 10^20 cm^-2
Excess significance: 2.4 sigma
Photon index:         2.0 (+0.7, -0.6)

Further observations by Swift are ongoing. The results of the XRT-team 
automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020234.

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