GCN Circular 14263
Subject
GRB 130305A: Swift/XRT detection of the afterglow
Date
2013-03-06T15:50:04Z (11 years ago)
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.