[vsnet-grb-info 7867] GRB 090519: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9411
SUBJECT: GRB 090519: Swift-XRT refined analysis
DATE:    09/05/20 15:17:58 GMT
FROM:    Matteo Perri at ISAC/ASDC  <perri at asdc.asi.it>

M. Perri, V. D'Elia, G. Stratta (ASDC) report on behalf of the
Swift-XRT team:

We have analysed the first 17 ks of XRT data for GRB 090519 (Perri et al.,
GCN Circ. 9400), from 121 s to 37 ks after the BAT trigger. The first
41 seconds of data are in Windowed Timing (WT) mode and at later times
in Photon Counting (PC) mode. The enhanced XRT position for this burst
was given by Goad et al. (GCN. Circ. 9405).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.8 (+/-0.2). At around T+580 s the decay
flattens to an alpha of 0.6 (+/-0.3) before breaking again at about
T+2 ks to a final decay with index alpha=1.4 (+0.3)(-0.2).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.5 (+/-0.2). The best-fitting
intrinsic absorption column at z=3.85 (Thoene et al., GCN Circ. 9409)
is 1.9(+1.7,-1.6)e22 cm^-2, in excess of the Galactic value of
3.0e20 cm^-2 (Kalberla et al. 2005). The counts-to-observed (-unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum is
4.9e-11 (5.4e-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
1.4, the count rate at T+24 hours will be 3e-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of
1.5e-14 (1.6e-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00352648.

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