[vsnet-grb-info 8721] GRB 091130B: Swift-XRT team refined analysis
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Tue Dec 1 16:37:52 JST 2009
TITLE: GCN CIRCULAR
NUMBER: 10222
SUBJECT: GRB 091130B: Swift-XRT team refined analysis
DATE: 09/12/01 07:37:46 GMT
FROM: Kim Page at U.of Leicester <kpa at star.le.ac.uk>
K.L. Page (U. Leicester) and J. L. Racusin (NASA/GSFC) report on behalf of
the Swift-XRT team:
We have analysed 12 ks of XRT data for GRB 091130B (Racusin et al. GCN
Circ. 10214), from 91 s to 29.1 ks after the BAT trigger. The data
comprise 155 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given by
Goad et al. (GCN. Circ 10218).
The light curve can be modelled with a series of power-law decays. The
initial index is alpha=-0.36 (+0.87, -1.14) - i.e., the light curve rises
slightly. At T+107 s the light curve starts decaying with an alpha of 3.58
(+0.24, -0.17). The light curve breaks again at T+172 s to a decay with
alpha=2.11 (+0.24, -0.06), before a final break at T+4020 s, after which
the decay index is 0.32 (+0.10, -0.11).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.26 (+0.07, -0.06). The
best-fitting absorption column is 2.32 (+/-0.17) x 10^21 cm^-2, in excess
of the Galactic value of 8.0 x 10^19 cm^-2 (Kalberla et al. 2005). The PC
mode spectrum has a photon index of 2.48 (+0.18, -0.19) and a best-fitting
absorption column of 1.66 (+0.23, -0.43) x 10^21 cm^-2. The counts to
observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum is 3.2 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1.
If the light curve continues to decay with a power-law decay index of
0.32, the count rate at T+24 hours will be 0.030 count s^-1, corresponding
to an observed (unabsorbed) 0.3-10 keV flux of 9.6 x 10^-13 (1.7 x 10^-12)
erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00377487.
This circular is an official product of the Swift-XRT team.
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