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
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 ),  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.