[vsnet-grb-info 15652] GRB 141022A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16941
SUBJECT: GRB 141022A: Swift-XRT refined Analysis
DATE:    14/10/22 13:48:04 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

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

We have analysed 10 ks of XRT data for GRB 141022A (Vargas  et al. GCN
Circ. 16938),  from 144 s to 25.5 ks after the	BAT trigger. The data
are entirely 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 = 241.8696, -72.1254 which is equivalent to:

RA (J2000): 16 07 28.70
Dec(J2000): -72 07 31.4

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.21 (+/-0.08).

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, -0.4). The
best-fitting absorption column is  1.1 (+0.5, -0.4) x 10^22 cm^-2, in
excess of the Galactic value of 1.0 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.9 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.1 (+0.5, -0.4) x 10^22 cm^-2
Galactic foreground: 1.0 x 10^21 cm^-2
Excess significance: 4.5 sigma
Photon index:	     2.5 (+0.5, -0.4)

If the light curve continues to decay with a power-law decay index of
1.21, the count rate at T+24 hours will be 2.7 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x
10^-14 (3.3 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00616061.

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