GCN Circular 16388

P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team:

We have analysed 11 ks of XRT data for GRB 140610A (Evans  et al. GCN
Circ. 16375
Not found
 
 
),  from 3.1 ks to 115.0 ks after the  BAT trigger. The data
comprise 586 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 463 s of PC mode data and 1 UVOT
image, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
286.26899, +3.90822 which is equivalent to:

RA (J2000): 19h 05m 04.56s
Dec(J2000): +03d 54' 29.6"

with an uncertainty of 3.1 arcsec (radius, 90% confidence).

The light curve from T0+3.1-10.6 ks can be modelled with  a power-law
decay with a decay index of alpha=0.66 (+0.26, -0.25). At T0+10.6 ks
the count rate is 0.04 +/- 0.01 ct/sec. In subsequent observations,
spanning T0+61-115 ks and containing 7.5 ks of exposure, the source is
undetected with a 3-sigma upper limit of 0.002 ct/sec. This is
substantially below the extrapolated decay detailed above, and suggests
a decay index of alpha > 1.71.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.3 (+0.9, -0.8). The
best-fitting absorption column is 3.1 (+2.0, -1.4) x 10^22 cm^-2, in
excess of the Galactic value of 1.2 x 10^22 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 6.0 x 10^-11 (2.0 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+2.0, -1.4) x 10^22 cm^-2
Galactic foreground: 1.2 x 10^22 cm^-2
Excess significance: 2.2 sigma
Photon index:	     2.3 (+0.9, -0.8)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00601259.

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