GCN Circular 37908

P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi 
(INAF-IASFPA) , J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams
(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 7.6 ks of XRT data for GRB 241026A, from 98 s to 45.9
ks after the  BAT trigger. The data comprise 54 s in Windowed Timing
(WT) mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.5 (+0.5, -0.4). At T+226 s  the decay
flattens to an alpha of 0.21 (+0.11, -0.12) before breaking again at
T+7943 s to a final decay with index alpha=0.90 (+/-0.11).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.88 (+/-0.10). The
best-fitting absorption column is  1.43 (+0.32, -0.30) x 10^21 cm^-2,
in excess of the Galactic value of 8.9 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 (4.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.43 (+0.32, -0.30) x 10^21 cm^-2
Galactic foreground: 8.9 x 10^20 cm^-2
Excess significance: 3.0 sigma
Photon index:	     1.88 (+/-0.10)

If the light curve continues to decay with a power-law decay index of
0.90, the count rate at T+24 hours will be 0.10 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x
10^-12 (4.7 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/01262764.

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