GCN Circular 7532

M. Perri and G. Stratta (ASDC) report on behalf of the Swift XRT team:

We have analysed the first 3 orbits of Swift XRT data of the BAT GRB
080328 (Perri et al., GCN Circ. 7525
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 ). The data consist of 151 s in
Windowed Timing (WT) mode, from  T+108s to T+259s, and of
6.9 ks in Photon Counting (PC) mode thereafter.

The best XRT position is the UVOT-enhanced position reported by
Beardmore et al. (GCN Circ. 7527
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 ).

The early 0.3-10 keV X-ray light curve in WT mode shows a rapid decay.
Starting from T+260s up to T+13.7ks the curve is well fit by a broken
power-law model with decay indices alpha1=-0.57 (+0.09) (-0.06),
alpha2=-1.10 (+/-0.05) and a temporal break at (1.7+/-0.3) ks.

The WT X-ray spectrum is well fit by an absorbed power-law model
with a photon index of 2.1 (+/-0.1), a column density of
(4.2+/-0.4)e21 cm**-2 and an average observed 0.3-10 keV flux
of 9.3e-10 erg/cm**2/s. The PC X-ray spectrum during the first orbit,
from  T+260s to T+2106s, is also well fit by an absorbed power-law
model with a photon index of 2.2 (+/-0.1) and a column density of
(5.0+/-0.6)e21 cm**-2. The observed 0.3-10 keV flux for this spectrum
is 1.5e-10 erg/cm**2/s. We note the Galactic column density in the
direction of the source is 3.4e21 cm**-2.

Assuming the X-ray emission continues to decline at the same rate, we
predict a 0.3-10 keV XRT count rate of 0.03 count/s at T+24hr, which
corresponds to an observed 0.3-10 keV flux of about
1.4e-12 erg/cm**2/s.

This circular is an official product of the Swift XRT Team.