[see also ATel#7755 (Segreto, Del Santo, D'ai', La Parola, Cusumano, Mineo, Malzac)]
We have analysed about 13 days (from MJD 57189 until MJD 57201)
of BAT survey data on the recent outburst of V404 Cyg (Atel #7646).
A very bright X-ray flare (Swift/XRT observation reported in ATel #7736)
has been observed with Swift/BAT at MJD 57199.533 (2015/06/26 12:47 UT)
with a peak intensity of about 50 Crab in 15-30 keV.
This occurred about 14 hours after the giant radio flare reported in the ATel #7716.
In spite of the short exposure time (2 min),
we obtained a very good statistics spectrum at the flare peak, which extends
up to 200 keV.
The 15-200 keV spectrum can be well described (Chi^2_red=1.19(72)) by a
a cutoff power-law with Ec= 78 +12-10 keV,
Γ=2.21±0.07 plus
a reflection component with Ω/2π=1.2 +0.2/-0.3.
The estimated 15-200 keV flux is 6.8E-7 erg/cm2/s
which translates into a luminosity of 4.6E+38 erg/s, assuming a distance of
2.4 kpc (Miller-Jones, J. et al., ApJL, 706, 230).
Extrapolation of this model over the range 1-500 keV results in a luminosity
of 1.6E+39 erg/s which is
consistent with the Eddington luminosity of a 12 M_Sun black hole system
(Shahbaz, T. et al., 1994, MNRAS, 271, L1).
Products obtained from the BAT data are available upon request to the following address:
bat@ifc.inaf.it
BAT light curve on V404 Cyg in two energy bands
BAT spectrum of V404 Cyg collected during the peak of the last flare
(integration time is 2 min)
The Palermo BAT survey project
- Webmaster: F. D'Anna
