GCN Circular 43291

P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), S. Lanava (PSU), S.
Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L.
Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi 
(INAF-IASFPA)  and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 260101A, from 100 s to 28.9
ks after the   trigger. The data comprise 165 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 late-time light curve (from T0+5.3 ks) can be modelled with a
power-law decay with a decay index of alpha=1.65 (+/-0.17).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.02 (+0.16, -0.15). The
best-fitting absorption column is  2.1 (+/-0.5) x 10^21 cm^-2,
consistent with the Galactic value of 1.6 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 1.91 (+0.16,
-0.15) and a best-fitting absorption column of 2.2 (+0.6, -0.5) 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 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^21 cm^-2
Excess significance: 1.8 sigma
Photon index:	     1.91 (+0.16, -0.15)

If the light curve continues to decay with a power-law decay index of
1.65, the count rate at T+24 hours will be 3.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x
10^-13 (2.0 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01429608.

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