GCN Circular 45822

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai
(INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), S. Lanava
(PSU), S. Dichiara (PSU), D.N. Burrows (PSU), A.P. Beardmore (U.
Leicester) and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 5.1 ks of XRT data for GRB 261005B, from 4.4 ks to
81.3 ks after the   trigger. The data are entirely in Photon Counting
(PC) mode. Using 3116 s of PC mode data and 6 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 255.33918, +1.58871
which is equivalent to:

RA (J2000): 17h 01m 21.40s
Dec(J2000): +01d 35' 19.4"

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial rise, with a power-law
index of alpha=-1.5 (+0.0, -1.0), followed by a break at T+8550 s  to
an alpha of 2.7 (+0.6, -0.5).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.15 (+/-0.13). The
best-fitting absorption column is  1.5 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 9.0 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 6.1 x 10^-11 (6.5 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.5 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 9.0 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index:	     1.15 (+/-0.13)

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01515414.

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