[vsnet-grb-info 13727] GRB 130725A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15042
SUBJECT: GRB 130725A: Swift-XRT refined Analysis
DATE:    13/07/26 15:28:18 GMT
FROM:    Binbin Zhang at PSU  <bbzhang at psu.edu>

B.-B. Zhang (PSU/UAH)  reports on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 130725A,  from 3.1 ks to
17.2 ks after the  BAT trigger. The data are entirely in Photon
Counting (PC) mode. Using 3850 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 =
230.03240, +0.62761 which is equivalent to:

RA (J2000): 15h 20m 07.78s
Dec(J2000): +00d 37' 39.4"

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=0.7 (+0.4, -0.3).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.5 (+0.6, -0.5). The
best-fitting absorption column is  9 (+11, -5) x 10^20 cm^-2,
consistent with the Galactic value of 4.3 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 2.9 x 10^-11 (4.5 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9 (+11, -5) x 10^20 cm^-2
Galactic foreground: 4.3 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.5 (+0.6, -0.5)

If the light curve continues to decay with a power-law decay index of
0.7, the count rate at T+24 hours will be 2.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.5 x
10^-14 (1.3 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00563980.

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