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GCN Circular 14788

Subject
GRB 130605A: Swift-XRT refined Analysis
Date
2013-06-06T23:36:06Z (11 years ago)
From
Andrea Melandri at INAF-OAB <andrea.melandri@brera.inaf.it>
A. Melandri (INAF/OAB) and S. T. Holland (STScI) report on behalf of
the Swift-XRT team:

We have analysed 15 ks of XRT data for GRB 130605A (Holland  et al. GCN
Circ. 14773),  from 78 s to 58.5 ks after the  BAT trigger. The data
comprise 385 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 6133 s of PC mode data and 5 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 = 134.53571, -33.46152
which is equivalent to:

RA (J2000): 08h 58m 08.57s
Dec(J2000): -33d 27' 41.5"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.23 (+/-0.05).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.3 (+0.5, -0.3). The
best-fitting absorption column is  2.35 (+1.96, -0.16) x 10^21 cm^-2,
consistent with the Galactic value of 2.2 x 10^21 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 2.7 x 10^-11 (5.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     2.35 (+1.96, -0.16) x 10^21 cm^-2
Galactic foreground: 2.2 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.3 (+0.5, -0.3)

If the light curve continues to decay with a power-law decay index of
1.23, the count rate at T+24 hours will be 9.4 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x
10^-14 (4.7 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00557508.

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