[vsnet-grb-info 7744] GRB 090429B: Swift XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9298
SUBJECT: GRB 090429B: Swift XRT refined analysis
DATE:    09/04/29 20:14:12 GMT
FROM:    Antonia Rowlinson at U.of Leicester  <bar7 at star.le.ac.uk>

A. Rowlinson (U. Leicester) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift-XRT team:

We have analysed 8.9 ks of XRT data for GRB 090429B (Ukwatta et al. GCN
Circ. 9281), from 104 s to 29.9 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Beardmore et al. (GCN. Circ 9288).

The light curve initially shows a slow rise, which can be fitted with a
power-law of index 0.89 (+0.36, -0.46). At around T+642 s the light
curve breaks to a power-law decay, with index 1.20 (+0.11, -0.10).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.00 (+0.15, -0.24). The
best-fitting absorption column is 10.0 (+4.2, -5.3) x 10^20, in excess
of the Galactic value of 1.2 x 10^20 cm^-2 (Kalberla et al. 2005). The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.8 x 10^-11 (4.9 x 10^-11) erg cm^-2
count^-1.

If the light curve continues to decay with a power-law decay index of
1.20, the count rate at T+24 hours will be 0.0014 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.3 x
10^-14 (6.9 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/00350854.

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