[vsnet-grb-info 12125] GRB 120724A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13514
SUBJECT: GRB 120724A: Swift-XRT refined Analysis
DATE:    12/07/24 18:50:07 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli  (INAF-IASFPA),
J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), A.P. Beardmore
(U. Leicester), P.A. Evans (U. Leicester), O.M. Littlejohns (U.
Leicester) and P.D'Avanzo report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 120724A (D'Avanzo  et al.
GCN Circ. 13510), from 115 s to 13.0 ks after the  BAT trigger. The
data comprise 40 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The best available XRT position  (using the
promptly downlinked event data, the XRT-UVOT alignment and matching
UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 245.1800,
3.5081 which is equivalent to:

RA (J2000): 16 20 43.19
Dec(J2000): +03 30 29.0

with an uncertainty of 2.2 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.78 (+/-0.22), followed by a break at T+851 s to an
alpha of 0.48 (+0.18, -0.79).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.88 (+0.20, -0.09). The
best-fitting absorption column is  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 3.7 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 4.3 x 10^20 cm^-2
Intrinsic column:    0 (+9.3, -0) x 10^20 cm^-2 at z=1.48
Photon index:	     1.88 (+0.20, -0.09)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00528443.

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