TITLE:   GCN CIRCULAR
NUMBER:  26685
SUBJECT: GRB 200107B: Swift-XRT refined Analysis
DATE:    20/01/09 14:15:43 GMT
FROM:    Paolo D'Avanzo at INAF - OAB  <paolo.davanzo@inaf.it>

M. Perri (ASDC), V. D'Elia (ASDC), B. Sbarufatti (PSU), D.N. Burrows
(PSU), J. D. Gropp (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), A. D'Ai (INAF-IASFPA) and M. G. Bernardini (INAF-OAB)
report on behalf of the Swift-XRT team:

We have analysed 3.4 ks of XRT data for GRB 200107B (Bernardini et al.
GCN Circ. 26661), from 908 s to 139.6 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The refined XRT
position is RA, Dec = 106.9086, -83.7162 which is equivalent to:

RA (J2000): 07 07 38.07
Dec(J2000): -83 42 58.3

with an uncertainty of 4.0 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.0 (+0.3, -0.4).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.9 (+0.5, -0.4). The
best-fitting absorption column is  2.8 (+2.4, -1.3) x 10^21 cm^-2,
consistent with the Galactic value of 1.5 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 (5.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.8 (+2.4, -1.3) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.9 (+0.5, -0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00948219.

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