[vsnet-grb-info 6810] GRB 081024: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8405
SUBJECT: GRB 081024: Swift-XRT refined analysis
DATE:    08/10/24 20:31:08 GMT
FROM:    Matteo Perri at ISAC/ASDC  <perri at asdc.asi.it>

G. Stratta (ASDC) reports on behalf of the Swift-XRT team:

We have analysed the first orbit of the XRT data obtained for
GRB 081024 (Stratta et al., GCN Circ. 8398). From T+78 s to T+105 s
after the burst, data were collected in Windowed Timing mode and
then XRT switched to Photon Counting mode. The Enhanced Swift-XRT
position was given by Beardmore et al. in GCN Circ. 8403.

The 0.3-10 keV flux from T+78 s to T+355 s shows a very steep decay with
a possible small re-brightening between ~T+145 s to ~T+205 s. Excluding
the re-brightening and assuming a power law decay, the best fit decay
index is alpha = 3.7 (+0.8,-0.5).

The spectrum of the WT data, with an integration time of 27s, can
be modelled with a power-law model with photon index of 1.6 (+0.6,- 0.3).
The total absorbing equivalent hydrogen column density is consistent
with the Galactic one NH = 7.71E+21 cm^-2 (Kalberla et al. 2005). The
observed (unabsorbed) 0.3-10 keV flux is 4.1(6.1)E-10 erg/cm^-2 s^-1

No source counts are detected after the first orbit, likely due to
the very steep flux decay.

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