[vsnet-grb-info 13505] GRB 130608A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14838
SUBJECT: GRB 130608A: Swift-XRT refined Analysis
DATE:    13/06/09 17:28:07 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

K.L. Page (U. Leicester), C. Pagani (U. Leicester), V. Mangano
(INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU),
M.C. Stroh (PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), A.P. Beardmore
(U. Leicester) and H.A. Krimm report on behalf of the Swift-XRT team:

We have analysed 9.4 ks of XRT data for GRB 130608A (Krimm  et al. GCN
Circ. 14827),  from 147 s to 47.3 ks after the	BAT trigger. The data
comprise 98 s in Windowed Timing (WT) mode (the first 10 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN. Circ 14832).

The light curve can be modelled with an initial power-law decay with an
index of alpha=4.33 (+0.26, -0.23), followed by a break at T+653 s to
an alpha of 0.40 (+0.11, -0.12).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.23 (+0.27, -0.25). The
best-fitting absorption column is  1.0 (+0.4, -0.3) x 10^21 cm^-2, in
excess of the Galactic value of 6.6 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.40 (+0.36, -0.11)
and a best-fitting absorption column consistent with the Galactic
value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.0 x 10^-11 (4.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     0 (+4.9, -0) x 10^20 cm^-2
Galactic foreground: 6.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.40 (+0.36, -0.11)

If the light curve continues to decay with a power-law decay index of
0.40, the count rate at T+24 hours will be 7.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x
10^-13 (3.0 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/00557771.

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