TITLE:   GCN CIRCULAR
NUMBER:  9052
SUBJECT: GRB 090328: Swift XRT refined analysis
DATE:    09/03/29 20:39:01 GMT
FROM:    Antonia Rowlinson at U.of Leicester  <bar7@star.le.ac.uk>

A. Rowlinson and K. Page (U. Leicester) report on behalf of the
Swift/XRT Team:

We have analysed 3.4 ks of XRT data for the Fermi GBM and LAT detected
GRB 090328 (McEnery et al. GCN Circ. 9044, Kennea et al. GCN Circ.
9045), from 57.1 ks to 94.3 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode.

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.60 (+/-0.28).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.9 (+0.3, -0.4). The
best-fitting absorption column is 1.9 (+1.4, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 5.0 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 4.9 x 10^-11 (6.6 x 10^-11) erg
cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
2.60, the count rate at T+48 hours will be 0.004 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.96 x
10^-13(2.64 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/00031387.

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