GCN Circular 43539

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

We have analysed 9.4 ks of XRT data for GRB 260127A, from 226 s to 51.7
ks after the   trigger. The data comprise 102 s in Windowed Timing (WT)
mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.  The late-time light curve
(from T0+5.2 ks) is consistent with a constant source of mean count
rate 3.6e+00 ct/sec. A power-law fit gives an index of 3.08 (+0.03,
-3.08).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.14 (+0.20, -0.19). The
best-fitting absorption column is  8.0 (+4.6, -3.9) x 10^20 cm^-2, in
excess of the Galactic value of 4.1 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.75 (+/-0.06) and a
best-fitting absorption column of 1.32 (+0.21, -0.20) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.0 x 10^-11 (4.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.32 (+0.21, -0.20) x 10^21 cm^-2
Galactic foreground: 4.1 x 10^20 cm^-2
Excess significance: 7.6 sigma
Photon index:	     1.75 (+/-0.06)

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01444088.

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