GCN Circular 31355

A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D.
Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato
(INAF-OAB) and A. Tohuvavohu report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 220101A (Tohuvavohu et al.
GCN Circ. 31347
Loading...
 
 ), from 73 s to 34.6 ks after the  BAT trigger. The data
comprise 322 s in Windowed Timing (WT) mode (the first 6 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN Circ. 31349
Loading...
 
 ).

The late-time light curve (from T0+3.6 ks) can be modelled with an
initial power-law decay with an index of alpha=1.6 (+0.8, -0.4),
followed by a break at T+4385 s to an alpha of 5.8 (+0.6, -0.4).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.519 (+0.023, -0.016). The
best-fitting absorption column is  consistent with the Galactic value
of 6.3 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.59 (+/-0.07) and a best-fitting absorption column
of 7 (+12, -7) x 10^21 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 4.2 x
10^-11 (4.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 6.3 x 10^20 cm^-2
Intrinsic column:    7 (+12, -7) x 10^21 cm^-2 at z=4.61
Photon index:	     1.59 (+/-0.07)

If the light curve continues to decay with a power-law decay index of
5.8, the count rate at T+24 hours will be 2.8 x 10^-7 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-17 (1.3 x 10^-17) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01091527.

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