GCN Circular 35470

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G.
Bernardini (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), A.
Tohuvavohu (U. Toronto) and P.A. Evans report on behalf of the
Swift-XRT team:

We have analysed 6.9 ks of XRT data for GRB 240101B, from 138 s to
126.6 ks after the  BAT trigger. The data comprise 189 s in Windowed
Timing (WT) mode (the first 12 s were taken while Swift was slewing)
with the remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+5.0 ks) can be modelled with a
power-law decay with a decay index of alpha=0.80 (+0.33, -0.29).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.28 (+0.14, -0.13). The
best-fitting absorption column is  6.5 (+/-0.8) x 10^21 cm^-2, in
excess of the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.39 (+0.29, -0.27)
and a best-fitting absorption column of 7.9 (+2.0, -1.8) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.8 x 10^-11 (9.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.9 (+2.0, -1.8) x 10^21 cm^-2
Galactic foreground: 2.9 x 10^21 cm^-2
Excess significance: 4.7 sigma
Photon index:	     2.39 (+0.29, -0.27)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01205744.

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