TITLE:   GCN CIRCULAR
NUMBER:  35391
SUBJECT: GRB 231216A: Swift-XRT refined Analysis
DATE:    23/12/17 19:18:04 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB),
J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore
(U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on
behalf of the Swift-XRT team:

We have analysed 6.1 ks of XRT data for GRB 231216A, from 115 s to 68.0
ks after the  BAT trigger. The data comprise 8 s in Windowed Timing
(WT) mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode. The refined XRT position is RA, Dec = 39.7727,
+33.5764 which is equivalent to:

RA (J2000): 02 39 05.45
Dec(J2000): +33 34 35.0

with an uncertainty of 3.9 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.7 (+nan, -nan).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+0.4, -0.3). The
best-fitting absorption column is  3.2 (+1.7, -1.4) x 10^21 cm^-2, in
excess of the Galactic value of 8.4 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.7 x 10^-11 (5.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.2 (+1.7, -1.4) x 10^21 cm^-2
Galactic foreground: 8.4 x 10^20 cm^-2
Excess significance: 2.8 sigma
Photon index:	     2.1 (+0.4, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01202749.

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