GCN Circular 7694

B. Sbarufatti, V. Mangano, V. La Parola (INAF-IASF PA) and
W. H. Baumgartner (GSFC/UMBC)

The Swift-XRT began observing GRB 080506 (trigger=311159, Baumgartner
et al., GCN Circ. 7685
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 ) in Window Timing mode, 146 s after the BAT
trigger. The enhanced XRT position was given in Osborne et al.
(GCN Circ. 7687
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 ).

The lightcurve is quite complex. It shows two initial bright flares
centered at 182+/-2 s and 254+/-2 s, with folding times of 22+/-1 s
and 88+/-2 s, respectively. Flaring activity is detected until times
 > T+10 ks. The decay slope after 10 ks from the trigger time is
-0.6+/-0.2.

The spectrum of the first flare can be fit by a power-law model, with
a photon index of 1.46 � 0.06 and column density consistent with the
average Galactic column density in this direction of 1.66e21 cm-2
(Kalberla et al 2005). The observed (unabsorbed) 0.3-10 keV flux is
1.5e-9 (1.8e-9) erg cm-2 s-1.

The spectrum of the second flare can be fit by a power-law model, with
a photon index of 2.3 � 0.1 and column density consistent with the
average Galactic column density in this direction. The observed
(unabsorbed) 0.3-10 keV flux is 3.2e-10 (5.2e-9) erg cm-2 s-1.

The PC mode spectrum, covering times > T+1000 s, is fit by a power
law model with photon index 2.0 � 0.2 and no evidence for any
additional column density with respect to the Galactic one.
The corresponding observed (unabsorbed) 0.3-10 keV fluxes are
2.3e-12 (3.5e-12 ) erg cm-2 s-1, respectively.

If the burst continues to decay at the same rate, we predict an XRT
count rate of 9.8 e-3 counts/s and 6.4 e-3 counts/s at T+24 hours
and T+48 hours, respectively. This corresponds to observed 0.3-10
keV fluxes of approximately 5.4e-13 and 3.6e-13 erg cm-2 s-1.

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