GCN Circular 37988

E. Ambrosi  (INAF-IASFPA) , M. A. Williams (PSU), S. Dichiara (PSU),
J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester), M. Capalbi (INAF-IASFPA), M.
Perri (SSDC & INAF-OAR) and P.A. Evans report on behalf of the
Swift-XRT team:

We have analysed 11 ks of XRT data for GRB 241030A, from 63 s to 45.7
ks after the  BAT trigger. The data comprise 859 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 late-time light curve (from T0+4.5 ks) can be modelled with an
initial power-law decay with an index of alpha=0.87 (+0.17, -0.57),
followed by a break at T+10.4 ks to an alpha of 1.58 (+/-0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.720 (+0.016, -0.011). The
best-fitting absorption column is  consistent with the Galactic value
of 1.8 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.95 (+0.08, -0.06) and a best-fitting absorption
column consistent with the Galactic value. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 3.6 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.8 x 10^21 cm^-2
Intrinsic column:    1.8 (+1.8, -0.0) x 10^21 cm^-2 at z=1.411
Photon index:	     1.95 (+0.08, -0.06)

If the light curve continues to decay with a power-law decay index of
1.58, the count rate at T+24 hours will be 0.034 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-12 (1.6 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/01263718.

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