[vsnet-grb-info 18644] GRB 161022A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20092
SUBJECT: GRB 161022A: Swift-XRT refined Analysis
DATE:    16/10/22 12:26:37 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

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

We have analysed 8.7 ks of XRT data for GRB 161022A (Stamatikos et al.
GCN Circ. 20087), from 118 s to 22.5 ks after the  BAT trigger. The
data comprise 7 s in Windowed Timing (WT) mode (taken while Swift was
slewing), 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 = 129.0017, 54.3486 which is equivalent to:

RA (J2000): 08 36 00.40
Dec(J2000): +54 20 55.0

with an uncertainty of 2.0 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.46 (+0.13, -0.11).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.70 (+0.16, -0.07). The
best-fitting absorption column is  consistent with the Galactic value
of 4.1 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 3.8 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.1 (+/-2.0) x 10^20 cm^-2
Galactic foreground: 4.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.70 (+0.16, -0.07)

If the light curve continues to decay with a power-law decay index of
1.46, the count rate at T+24 hours will be 1.5 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.6 x
10^-15 (5.9 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00718655.

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