GCN Circular 19904

A. D'A�  (INAF-IASFPA), V. D'Elia (ISDC), J. Cummings (GSFC/UMBC),
B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU),
S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the Fermi/GBM (Veres 
et al., GCN Circ. 19901
Not found
 
 
)
and Fermi/LAT (Racusin et al., GCN Circ. 19902
Not found
 
 
) detected burst GRB 
160910A in a series of 4 observations
tiled on the sky. The total exposure time is 5 ks, distributed over 4 
tiles.
The data were collected between T0+35 ks and T0+47 ks, and are entirely 
in Photon Counting (PC) mode.

An uncatalogued X-ray source is detected and is above the RASS limit, 
and is therefore likely the GRB afterglow.
The position of this source is RA, Dec.=221.4423, 39.0668 which is 
equivalent to:

RA (J2000)   = 14h45m46.16s
Dec (J2000) = +39:04:00.64

with an uncertainty of 4.3 arcsec (radius, 90% confidence).
This position is 0.34 deg from the Fermi/LAT position and 0.6 deg from 
the GBM position.
The light curve built with the data collected so far is consistent with 
a constant source of mean
count rate (1.0 +/- 0.1)e-01 ct/sec. More data are required to search 
for a fading behaviour.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.7 (+0.6, -0.6).
The best-fitting absorption column is  1.3 (+1.7, -1.3) x 10^21 cm^-2,
consistent with the Galactic value of 1.0 x 10^20 cm^-2 (Willingale et 
al. 2013).
The [absorbed] unabsorbed 0.3-10 keV flux is 5.1 (+1.6, -1.0)e^-10 erg 
cm^-2 s^-1 [4.7 (+2.1, -1.3) e-10 erg cm^-2 s^-1].

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