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) in Window Timing mode, 146 s after the BAT
trigger. The enhanced XRT position was given in Osborne et al.
(GCN Circ. 7687).
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
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.