GCN Circular 30208

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

We have analysed 5.8 ks of XRT data for GRB 210610B (Page et al. GCN
Circ. 30170
Not found
 
 
), from 87 s to 81.7 ks after the  BAT trigger. The data
comprise 1.3 ks in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 30189
Not found
 
 
).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.13 (+0.23, -0.34). At T+133 s  the decay
steepens to an alpha of 1.86 (+0.06, -0.05). The light curve breaks
again at T+397 s to a decay with alpha=0.77 (+0.06, -0.05),  before a
final break at T+1153 s s after which the decay index is 1.105 (+0.023,
-0.022).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.847 (+/-0.022). The
best-fitting absorption column is  4.4 (+/-2.5) x 10^20 cm^-2, at a
redshift of 1.13, in addition to the Galactic value of 3.9 x 10^20
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.92 (+/-0.12) and a best-fitting absorption column of 1.1 (+1.4,
-1.1) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.4 x 10^-11 (3.9
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 3.9 x 10^20 cm^-2
Intrinsic column:    1.1 (+1.4, -1.1) x 10^21 cm^-2 at z=1.13
Photon index:	     1.92 (+/-0.12)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01054681.

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