[vsnet-grb-info 12734] GRB 121217A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14093
SUBJECT: GRB 121217A: Swift-XRT refined Analysis
DATE:    12/12/17 21:32:04 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

P.A. Evans (U. Leicester), O.M. Littlejohns (U. Leicester), A. Melandri
(INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), G. Stratta (ASDC), M.C. Stroh
(PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester) and M.H. Siegel report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 121217A (Siegel  et al. GCN
Circ. 14089),  from 70 s to 30.3 ks after the  BAT trigger. The data
comprise 655 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN. Circ 14090).

The late-time light curve (from T0+5.5 ks) can be modelled with  a
power-law decay with a decay index of alpha=0.63 (+/-0.08).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.15 (+0.11, -0.08). The
best-fitting absorption column is  consistent with the Galactic value
of 3.7 x 10^21 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a
photon index of 1.92 (+0.11, -0.10) and a best-fitting absorption
column of 4.02 (+0.51, -0.30) x 10^21 cm^-2. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.6 x 10^-11 (7.3 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.02 (+0.51, -0.30) x 10^21 cm^-2
Galactic foreground: 3.7 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.92 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
0.52, the count rate at T+24 hours will be 0.091 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x
10^-12 (6.7 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/00542441.

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