[vsnet-grb-info 25823] GRB 200612A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27923
SUBJECT: GRB 200612A: Swift-XRT refined Analysis
DATE:    20/06/13 00:13:52 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A.
Tohuvavohu (U. Toronto), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), T.
Sbarrato (INAF-OAB) and E. Sonbas report on behalf of the Swift-XRT
team:

We have analysed 7.4 ks of XRT data for GRB 200612A (Sonbas et al. GCN
Circ. 27915), from 93 s to 63.5 ks after the  BAT trigger. The data
comprise 281 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 27921).

The late-time light curve (from T0+3.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.37 (+/-0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.07 (+/-0.05). The
best-fitting absorption column is  9.1 (+2.3, -2.1) x 10^20 cm^-2, in
excess of the Galactic value of 3.7 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.06 (+0.19, -0.17)
and a best-fitting absorption column of 5.7 (+4.1, -2.0) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.1 x 10^-11 (3.6 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.7 (+4.1, -2.0) x 10^20 cm^-2
Galactic foreground: 3.7 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.06 (+0.19, -0.17)

If the light curve continues to decay with a power-law decay index of
1.37, the count rate at T+24 hours will be 0.010 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.2 x
10^-13 (3.7 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00977310.

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