TITLE:   GCN CIRCULAR
NUMBER:  29295
SUBJECT: GRB 210112A: Swift-XRT refined Analysis
DATE:    21/01/12 17:20:18 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), M. Capalbi
(INAF-IASFPA), M. Perri (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N.
Burrows (PSU), J. D. Gropp (PSU), K.L. Page (U. Leicester) and E.
Ambrosi report on behalf of the Swift-XRT team:

We have analysed 8.5 ks of XRT data for GRB 210112A (Ambrosi et al. GCN
Circ. 29289), from 77 s to 46.0 ks after the  BAT trigger. The data
comprise 859 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 29290).

The late-time light curve (from T0+6.4 ks) can be modelled with a
power-law decay with a decay index of alpha=1.36 (+/-0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.56 (+/-0.03). The
best-fitting absorption column is  2.34 (+/-0.14) x 10^21 cm^-2, in
excess of the Galactic value of 9.5 x 10^19 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.01 (+0.10, -0.09)
and a best-fitting absorption column of 2.8 (+/-0.4) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.7 x 10^-11 (5.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.8 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 9.5 x 10^19 cm^-2
Excess significance: 12.3 sigma
Photon index:	     2.01 (+0.10, -0.09)

If the light curve continues to decay with a power-law decay index of
1.36, the count rate at T+24 hours will be 0.046 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-12 (2.3 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/01016881.

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