TITLE:   GCN CIRCULAR
NUMBER:  11381
SUBJECT: GRB 101024A: Swift XRT refined analysis 
DATE:    10/10/25 11:32:55 GMT
FROM:    Rhaana Starling at U of Leicester  <rlcs1@star.le.ac.uk>

R.L.C. Starling, P.A. Evans, K.L. Page (U. Leicester) and M. De Pasquale 
(UCL-MSSL) report on behalf of the Swift-XRT team:

We have analysed 11 ks of Swift XRT data for GRB 101024A (De Pasquale et 
al. GCN Circ. 11370), from 62 s to 57.2 ks after the BAT trigger. The data 
comprise 8 s in Windowed Timing (WT) mode (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 11372).

The light curve can be modelled with a series of power-law decays. The 
initial decay index is alpha=5.0 (+5.0, -3.9). At T+77 s the decay 
flattens to an alpha of -0.03 (+0.16, -0.18) before breaking again at 
T+870 s to a final decay with index alpha=1.30 (+0.10, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed 
power-law with a photon spectral index of 1.95 (+0.13, -0.10). The 
best-fitting absorption column is 1.06 (+0.29, -0.13) x 10^21 cm^-2, in 
excess of the Galactic value of 6.5 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 4.0 x 10^-11 (5.1 x 10^-11) erg cm^-2 
count^-1.

If the light curve continues to decay with a power-law decay index of 
1.30, the count rate at T+24 hours will be 6.0 x 10^-3 count s^-1, 
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.4 x 10^-13 
(3.1 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/00437016.

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