GCN Circular 37769

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

We have analysed 8.7 ks of XRT data for GRB 241010A, from 86 s to 68.0
ks after the  BAT trigger. The data comprise 9 s in Windowed Timing
(WT) mode (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=3.3 (+4.0, -0.9). At T+154 s  the decay
flattens to an alpha of 0.1 (+0.3, -0.4). The light curve breaks again
at T+535 s to a decay with alpha=5.2 (+2.8, -3.4),  and  again at T+677
s s to alpha=-0.6 (+0.4, -0.9),  before a final break at T+3672 s s
after which the decay index is 0.92 (+0.14, -0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.91 (+/-0.13). The
best-fitting absorption column is  2.0 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 3.9 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 3.8 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.0 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 3.9 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     1.91 (+/-0.13)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01259578.

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