[vsnet-grb-info 24175] GRB 191122A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26274
SUBJECT: GRB 191122A: Swift-XRT refined Analysis
DATE:    19/11/22 22:21:07 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), V. D'Elia
(ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea
(PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester) and B.
Sbarufatti report on behalf of the Swift-XRT team:

We have analysed 8.8 ks of XRT data for GRB 191122A (Sbarufatti et al.
GCN Circ. 26269), from 301 s to 23.9 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Evans et al. (GCN Circ. 26270).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.97 (+0.26, -0.31). At T+746 s  the decay
steepens to an alpha of 1.94 (+0.26, -0.10) before breaking again at
T+6109 s to a final decay with index alpha=-0.1 (+/-0.4).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.06 (+0.04, -0.03). The
best-fitting absorption column is  consistent with the Galactic value
of 1.0 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.12 (+0.08, -0.07) and a best-fitting absorption
column consistent with the Galactic value. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 5.6 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     10.0 (+15.8, -0.0) x 10^19 cm^-2
Galactic foreground: 1.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.12 (+0.08, -0.07)

If the light curve continues to decay with a power-law decay index of
-0.1, the count rate at T+24 hours will be 0.067 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x
10^-12 (3.8 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00938899.

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