GCN Circular 38562

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed 4.5 ks of XRT data for GRB 241213A, from 106 s to 33.0
ks after the  BAT trigger. The data comprise 275 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. 

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.59 (+0.07, -0.08), followed by a break at T+680 s to
an alpha of 1.20 (+0.16, -0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.89 (+/-0.10). The
best-fitting absorption column is  3.3 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 6.7 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.85 (+/-0.14) and a
best-fitting absorption column of 3.9 (+0.8, -0.7) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.3 x 10^-11 (6.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.9 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 6.7 x 10^20 cm^-2
Excess significance: 7.4 sigma
Photon index:	     1.85 (+/-0.14)

If the light curve continues to decay with a power-law decay index of
1.20, the count rate at T+24 hours will be 0.014 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.9 x
10^-13 (8.5 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/01274039.

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