[vsnet-grb-info 9628] GRB 100814A: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11096
SUBJECT: GRB 100814A: Swift-XRT refined analysis
DATE:    10/08/14 20:34:14 GMT
FROM:    Andy Beardmore at U Leicester  <apb at star.le.ac.uk>

A. P. Beardmore (U Leicester) and C. J. Saxton (MSSL-UCL) report on
behalf of the Swift-XRT team:

We have analysed 6.0 ks of XRT data for GRB 100814A (Beardmore et
al. GCN Circ. 11087), from 76 s to 28.6 ks after the BAT trigger. The
data comprise 721 s in Windowed Timing (WT) mode (the first 9 s were
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 11092).

The X-ray light curve initially rises by a factor of ~2 in count rate, 
reaching a broad peak at approximately T+160 s after the trigger, on top 
of which are superimposed three small flares at T+146, 176 and 220 s, 
respectively. At T+295 s the light curve falls with a steep decay of 
alpha=5.7 (+0.4, -0.3), then breaks to a shallow decay at T+517 s, after 
which it decays with an index of 0.47 (+0.03, -0.04).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.68 (+0.04, -0.03). The
best-fitting absorption column is 5.0 (+/-0.8) x 10^20 cm^-2, in
excess of the Galactic value of 1.8 x 10^20 cm^-2 (Kalberla et
al. 2005). The PC mode spectrum has a photon index of 1.90 (+0.11,
-0.10) and a best-fitting absorption column of 3.1 (+2.2, -1.4) x
10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.8 x 10^-11 (4.2 x
10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index 
of 0.47, the count rate at T+24 hours will be 0.18 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 
7.0 x 10^-12 (7.7 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/00431605.

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