[vsnet-grb-info 12017] GRB 120701A: Swift-XRT afterglow detection and analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13406
SUBJECT: GRB 120701A: Swift-XRT afterglow detection and analysis
DATE:    12/07/03 12:20:14 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed 19 ks of XRT data for GRB 120701A (Barthelmy et al. et
al. GCN Circ. 13404), from 61 s to 58.8 ks after the  BAT trigger. The
data comprise 69 s in Windowed Timing (WT) mode (the first 9 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. We find an uncatatalogued, fading X-ray source inside the
BAT error circle. Using 7344 s of PC mode data and 5 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 =
80.34740, -58.54973 which is equivalent to:

RA (J2000): 05h 21m 23.38s
Dec(J2000): -58d 32' 59.0"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.078 (+0.031, -0.030).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.06 (+0.22, -0.21). The
best-fitting absorption column is  1.6 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 2.5 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 3.7 x 10^-11 (5.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 2.5 x 10^20 cm^-2
Excess significance: 4.0 sigma
Photon index:	     2.06 (+0.22, -0.21)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00525477.

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