V. D'Elia (ASDC), M. de Pasquale (INAF-IASFPA), V. Mangano (PSU), M.C.
Stroh (PSU), D.N. Burrows (PSU), P.A. Evans (U. Leicester), B.P.
Gompertz (U. Leicester), J.P. Osborne (U. Leicester), A. Maselli
(INAF-IASFPA) and L.M.Z. Hagen report on behalf of the Swift-XRT team:
We have analysed 7.1 ks of XRT data for GRB 140709A (Hagen et al. GCN
Circ. 16546), from 75 s to 30.7 ks after the BAT trigger. The data
comprise 195 s in Windowed Timing (WT) mode (the first 6 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
The late-time light curve (from T0+5.7 ks) can be modelled with a
power-law decay with a decay index of alpha=0.89 (+0.08, -0.09).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.48 (+/-0.07). The
best-fitting absorption column is 9.9 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 4.1 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.88 (+/-0.14) and a
best-fitting absorption column of 8.0 (+1.2, -1.1) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 4.9 x 10^-11 (8.0 x 10^-11) erg cm^-2
A summary of the PC-mode spectrum is thus:
Total column: 8.0 (+1.2, -1.1) x 10^21 cm^-2
Galactic foreground: 4.1 x 10^21 cm^-2
Excess significance: 5.8 sigma
Photon index: 1.88 (+/-0.14)
If the light curve continues to decay with a power-law decay index of
0.89, the count rate at T+24 hours will be 0.038 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x
10^-12 (3.1 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
This circular is an official product of the Swift-XRT team.