[vsnet-grb-info 12702] GRB 121211A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14061
SUBJECT: GRB 121211A: Swift-XRT refined Analysis
DATE:    12/12/12 02:01:06 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

D.N. Burrows (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), A. Maselli  (INAF-IASFPA), A.
Melandri (INAF-OAB), J.A. Kennea (PSU), M.C. Stroh (PSU) and V. Mangano
report on behalf of the Swift-XRT team:

We have analysed 12 ks of XRT data for GRB 121211A (Mangano  et al. GCN
Circ. 14057),  from 95 s to 29.5 ks after the  BAT trigger. The data
comprise 203 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 14060).

The late-time light curve (from T0+3.9 ks) can be modelled with  a
power-law decay with a decay index of alpha=0.77 (+/-0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.15 (+/-0.04). The
best-fitting absorption column is  2.85 (+/-0.13) x 10^21 cm^-2, in
excess of the Galactic value of 9.5 x 10^19 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.11 (+0.15, -0.14)
and a best-fitting absorption column of 1.4 (+0.4, -0.3) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.5 x 10^-11 (5.0 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.4 (+0.4, -0.3) x 10^21 cm^-2
Galactic foreground: 9.5 x 10^19 cm^-2
Excess significance: 6.4 sigma
Photon index:	     2.11 (+0.15, -0.14)

If the light curve continues to decay with a power-law decay index of
0.76, the count rate at T+24 hours will be 0.025 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.9 x
10^-13 (1.3 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/00541200.

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