GCN Circular 18795

L. Izzo (URoma/ICRA), V. D'Elia (ASDC), P. D'Avanzo (INAF-OAB), T.G.R.
Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), A.P. Beardmore
(U. Leicester), S.L. Gibson (U. Leicester), A. D'Ai (INAF-IASFPA) and
P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 160101A (Itoh et al. GCN Circ. 18793
Not found
 
 
) in a series of
observations tiled on the sky. The total exposure time is 1.7 ks,
distributed over 7 tiles; the maximum exposure at a single sky location
was 512 s. The data were collected between T0+13.2 ks and T0+19.6 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=219.6506, -13.8154 which is equivalent to:

RA (J2000): 14:38:36.14
Dec(J2000): -13:48:55.5

with an uncertainty of 3.7 arcsec (radius, 90% confidence).  This
position is 4.8 arcmin from the MAXI position.	The source has a mean
count rate of 3.9e-01 ct/sec; we cannot determine at the present time
whether it is fading.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.5 (+0.5, -0.3). The
best-fitting absorption column is  1.20 (+2.17, -0.29) x 10^21 cm^-2,
consistent with the Galactic value of 9.1 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 4.6 x 10^-11 (5.1 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.20 (+2.17, -0.29) x 10^21 cm^-2
Galactic foreground: 9.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.5 (+0.5, -0.3)

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/xrt_products/TILED_GRB00051/index_1.php.
The results of the full analysis of the tiled XRT observations are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00051.

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