[vsnet-grb-info 7069] GRB 081210: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8652
SUBJECT: GRB 081210: Swift-XRT refined analysis
DATE:    08/12/11 09:02:37 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

P.A. Evans, K.L. Page (U. Leicester) and H.A. Krimm (CRESST/GSFC/USRA)
report on behalf of the Swift-XRT team:

We have analysed 4.9 ks of XRT data for GRB 081210 (Krimm et al., GCN
Circ. 8648), beginning 78 s after the BAT trigger. The first 387 s were
obtained in Windowed Timing (WT) mode and the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Osborne et al. (GCN Circ 8650).

The light curve shows an initial period of flaring activity. A strong
peak is seen at T+138 s coincident with the third peak seen by the BAT
(Barthelmy et al. GCN Circ. 8649). Further peaks are seen at T+219 s,
317 s and 391 s. During this time the underlying light curve, while
difficult to constrain, is clearly decaying, with a power-law index of
around 1.5. Around T+5000 s the decay flattens, to a slope of 0.74
(+/-0.24).

A spectrum formed from the PC mode data, i.e. after the flaring activity
has ceased, can be fitted with an absorbed power-law with a photon
index of 1.91 (+/-0.12). The best-fitting absorption column is 6.1
(+2.5, -1.5) x 10^20 cm^-2, consistent with the Galactic value in the
direction of the burst (4.6 x 10^20 cm^-2, Kalberla et al. 2005). The
counts to observed 0.3-10 keV flux conversion factor deduced from this
spectrum is 4.2 x 10^-11 erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
0.74, the count rate at T+24 hours will be 0.017 count s^-1,
corresponding to an observed (unabsorbed) flux of 6.73 x 10^-13 (8.02 x
10 ^-13) erg cm^-2 s^-1.

The results of the xrt automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00337073.

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