GCN Circular 35319

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Capalbi
(INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR),
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU) and
P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 231210B, from 410 s to 35.6
ks after the  BAT trigger. The data comprise 40 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.32 (+0.05, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.65 (+0.11, -0.10). The
best-fitting absorption column is  5.3 (+7.7, -5.3) x 10^21 cm^-2, at a
redshift of 3.13, in addition to the Galactic value of 4.1 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 4.0 x
10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 4.1 x 10^20 cm^-2
Intrinsic column:    5.3 (+7.7, -5.3) x 10^21 cm^-2 at z=3.13
Photon index:	     1.65 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
1.32, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x
10^-13 (1.9 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/01201696.

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