The Cygnus region of the Galactic plane contains many known supernova remnants, pulsars, X-ray and GeV gamma-ray emitters which make it a prime candidate for a Very High Energy (VHE) gamma-ray survey in the Northern Hemisphere. The VERITAS observatory, an array of four atmospheric Cherenkov telescopes located at the base of Mt. Hopkins in southern Arizona, USA, has carried out an extensive survey of the Cygnus region between 67 and 82 degrees in galactic longitude and between -1 and 4 degrees in galactic latitude. The survey, comprising more than 140 hours of observations, reaches an average VHE flux sensitivity of better than 4% of the Crab Nebula at energies above 200 GeV. Here we report on the preliminary results from this survey.
We propose a physical framework for interpreting the broad band power spectra
from black hole and neutron star binaries. We use the truncated disc/hot inner
flow geometry, and assume that the hot flow is generically turbulent. Each
radius in the hot flow produces fluctuations, and we further assume that these
are damped on the viscous frequency. Integrating over radii gives broad band
continuum noise power between low and high frequency breaks which are set by
the viscous timescale at the outer and inner edge of the hot flow,
respectively. Lense-Thirring (vertical) precession of the entire hot flow
superimposes the low frequency QPO on this continuum power.
We test this model on the power spectra seen in the neutron star systems
(atolls) as these have the key advantage that the (upper) kHz QPO most likely
independently tracks the truncation radius. These show that this model can give
a consistent solution, with the truncation radius decreasing from 20-8Rg while
the inner radius of the flow remains remarkably constant at 6Rg. This very
constrained geometry still does not quite completely determine the
Lense-Thirring precession frequency as this also depends on the radial
distribution of mass in the hot flow. Nonetheless, we show that this can be
consistent with the low frequency QPO, showing that the broad band power
spectra can be used as a diagnostic of accretion flows in strong gravity.
We review the formation scenarios for binary black holes, and show that their coalescence rate depends very strongly on the outcome of the second mass transfer. However, the observations of IC10 X-1, an binary with a massive black hole accreting from a Wolf-Rayet star proves that this mass transfer can be stable. We analyze the future evolution of IC10 X-1 and show that it is very likely to form a binary black hole system merging in a few Gyrs. We estimate the coalescence rate density of such systems to be $ 0.06 {\rm Mpc}^{-3} {\rm Myr}^{-1}$, and the detection rate for the current LIGO/VIRGO of $ 0.69 {\rm yr}^{-1} $, a much higher value than the expected double neutron star rate. Thus the first detection of a gravitational wave source is likely to be a coalescence of a binary black hole.
(Shortened) [...] After recalling the basic features of the "fireshell model", we emphasize the following novel results: 1) the interpretation of the X-ray flares in GRB afterglows as due to the interaction of the optically thin fireshell with isolated clouds in the CircumBurst Medium (CBM); 2) an interpretation as "fake - disguised" short GRBs of the GRBs belonging to the class identified by Norris & Bonnell [...] consistent with an origin from the final coalescence of a binary system in the halo of their host galaxies with particularly low CBM density [...]; 3) the first attempt to study a genuine short GRB with the analysis of GRB 050509B, that reveals indeed still an open question; 4) the interpretation of the GRB-SN association in the case of GRB 060218 via the "induced gravitational collapse" process; 5) a first attempt to understand the nature of the "Amati relation", a phenomenological correlation between the isotropic-equivalent radiated energy of the prompt emission E_{iso} with the cosmological rest-frame \nu F_{\nu} spectrum peak energy E_{p,i}. In addition, recent progress on the thermalization of the electron-positron plasma close to their formation phase, as well as the structure of the electrodynamics of Kerr-Newman Black Holes are presented. An outlook for possible explanation of high-energy phenomena in GRBs to be expected from the AGILE and the Fermi satellites are discussed. As an example of high energy process, the work by Enrico Fermi dealing with ultrarelativistic collisions is examined. It is clear that all the GRB physics points to the existence of overcritical electrodynamical fields. In this sense we present some progresses on a unified approach to heavy nuclei and neutron stars cores, which leads to the existence of overcritical fields under the neutron star crust.
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