GCN Circular 38209

A.P. Beardmore (U. Leicester), M. Ferro (INAF-OAB), R. Brivio
(INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), D.N. Burrows
(PSU), M. A. Williams (PSU), J.P. Osborne (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 241113A, from 60 s to 34.4
ks after the  BAT trigger. The data comprise 75 s in Windowed Timing
(WT) mode (the first 10 s were taken while Swift was slewing) 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=1.90 (+/-0.24), followed by a break at T+165 s to an
alpha of 0.92 (+0.04, -0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.32 (+0.33, -0.30). The
best-fitting absorption column is  2.2 (+1.1, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 2.0 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 3.2 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+1.1, -0.9) x 10^21 cm^-2
Galactic foreground: 2.0 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index:	     2.32 (+0.33, -0.30)

If the light curve continues to decay with a power-law decay index of
0.92, the count rate at T+24 hours will be 8.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x
10^-13 (4.1 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/01267501.

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