GCN Circular 16986
Subject
GRB 141028A: Swift-XRT observations
Date
2014-10-29T16:39:33Z (10 years ago)
From
Claudio Pagani at U of Leicester <cp232@star.le.ac.uk>
C. Pagani, K. L. Page and P. A. Evans (U. Leicester) report on behalf
of the Swift-XRT team:
We have analysed 3.0 ks of XRT data for the Fermi/LAT-detected burst:
GRB 141028A, from 31.0 ks to 71.7 ks after the Fermi/LAT trigger. The
data are entirely in Photon Counting (PC) mode. An X-ray source is
detected within the Fermi/LAT error circle. Using 348 s of PC mode data
and 1 UVOT images, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 322.60168, -0.23145 which is equivalent to:
RA (J2000): 21h 30m 24.40s
Dec(J2000): -00d 13' 53.2"
with an uncertainty of 4.0 arcsec (radius, 90% confidence). This
position is 367 arcsec from the Fermi/LAT position (Bissaldi et al. GCN
16969) and consistent with the positions of the optical counterpart
detected by MASTER (Gorbovskoy et al. GCN 16972), GROND (Graham et al.
GCN 16977) and UVOT (Siegel et al. GCN 16979).
The light curve can be modelled with a power-law decay with a decay
index of alpha=2.0 (+/-1.0).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.5 (+/-0.5). The
best-fitting absorption column is 1.8 (+2.2, -1.3) x 10^21 cm^-2, in
excess of the Galactic value of 4.1 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.0 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.8 (+2.2, -1.3) x 10^21 cm^-2
Galactic foreground: 4.1 x 10^20 cm^-2
Excess significance: 1.8 sigma
Photon index: 2.5 (+/-0.5)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020420.
This circular is an official product of the Swift-XRT team.