GCN Circular 19868

P.A. Evans (U. Leicester), A. D'Ai (INAF-IASFPA), A. Maselli 
(INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), S.L. Gibson (U. Leicester), J.P.
Osborne (U. Leicester) and B. Mingo report on behalf of the Swift-XRT
team:

We have analysed 6.5 ks of XRT data for GRB 160826A (Mingo et al. GCN
Circ. 19866
Not found
 
 
), from 93 s to 22.1 ks after the  BAT trigger. The data
comprise 114 s in Windowed Timing (WT) mode (the first 5 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The refined XRT position is RA, Dec = 183.1127, -67.6639 which is
equivalent to:

RA (J2000): 12 12 27.05
Dec(J2000): -67 39 50.0

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.64 (+0.06, -0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.68 (+0.31, -0.28). The
best-fitting absorption column is  9.1 (+3.3, -2.7) x 10^21 cm^-2, in
excess of the Galactic value of 4.6 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 5.7 x 10^-11 (8.5 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.1 (+3.3, -2.7) x 10^21 cm^-2
Galactic foreground: 4.6 x 10^21 cm^-2
Excess significance: 2.7 sigma
Photon index:	     1.68 (+0.31, -0.28)

If the light curve continues to decay with a power-law decay index of
1.64, the count rate at T+24 hours will be 2.1 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-14 (1.7 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00709907.

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