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GCN Circular 16475

Subject
GRB 140628A: Swift-XRT refined Analysis
Date
2014-06-29T06:59:22Z (10 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo, M.G. Bernardini, A. Melandri (INAF/OAB), P.A. Evans (U.
Leicester) and E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of
the Swift-XRT team:

We have analysed 8.2 ks of XRT data for GRB 140628A (Sonbas  et al. GCN
Circ. 16467),  from 231 s to 23.2 ks after the	BAT trigger. The data
comprise 47 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. Using 5310 s of PC mode data and 10 UVOT images, we
find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
40.66617, -0.38489 which is equivalent to:

RA (J2000): 02h 42m 39.88s
Dec(J2000): -00d 23' 05.6"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.21 (+0.03, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.88 (+0.19, -0.18). The
best-fitting absorption column is  8.9 (+5.3, -4.7) x 10^20 cm^-2, in
excess of the Galactic value of 3.2 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 3.5 x 10^-11 (4.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.9 (+5.3, -4.7) x 10^20 cm^-2
Galactic foreground: 3.2 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index:	     1.88 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
1.21, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (1.9 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00602803.

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