[vsnet-grb-info 18207] GRB 160703A: Swift-XRT afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19655
SUBJECT: GRB 160703A: Swift-XRT afterglow detection
DATE:    16/07/05 08:40:09 GMT
FROM:    Valerio D'Elia at ASDC  <delia at asdc.asi.it>

V. D'Elia (INAF-OAR), L. Izzo (IAA-CSIC), D. Malesani (DARK/NBI), E.
Troja (GSFC), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R.
Roegiers (PSU), B. Mingo (U. Leicester), A.P. Beardmore (U. Leicester),
A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Swift/BAT-detected burst GRB 160703A (Lien et al. GCN Circ. 19648),
collecting 5.0 ks of Photon Counting (PC) mode data between T0+107.8 ks
and T0+120.4 ks. 

An uncatalogued X-ray source is detected within the 3-sigma Swift/BAT
error region and is above the RASS limit, and is therefore likely the
GRB afterglow.	The position of this source is RA, Dec=287.4168,
+36.9175 which is equivalent to:

RA (J2000): 19:09:40.04
Dec(J2000): +36:55:03.0

with an uncertainty of 3.9 arcsec (radius, 90% confidence).  This
position is 92 arcsec from the Swift/BAT position and 5.1 arcsec from
the optical transient reported by Tachibana et al. (GCN Circ. 19652). 
The light curve is consistent with a constant source of mean count rate
1.7e-02 ct/sec. A power-law fit gives an index of 2.92 (+0.03, -3.89).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.9 (+0.7, -0.5). The
best-fitting absorption column is  3.0 (+3.9, -1.5) x 10^21 cm^-2,
consistent with the Galactic value of 1.5 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 3.9 x 10^-11 (5.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.0 (+3.9, -1.5) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.9 (+0.7, -0.5)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00702699.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00702699.

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