High-energy emission of fast rotating white dwarfs

The process of energy release in the magnetosphere of a fast rotating, magnetized white dwarf can be explained in terms of the canonical spin-powered pulsar model. Applying this model to the white dwarf companion of the low mass close binary AE Aquarii leads us to the following conclusions. First, the system acts as an accelerator of charged particles whose energy is limited to E_p < 3 TeV and which are ejected from the magnetosphere of the primary with the rate L_kin < 10^{32} erg/s. Due to the curvature radiation of the accelerated primary electrons the system should appear as a source of soft gamma-rays (~ 100 keV) with the luminosity < 3x10^{27} erg/s. The TeV emission of the system is dominated by the inverse Compton scattering of optical photons on the ultrarelativistic electrons. The optical photons are mainly contributed by the normal companion and the stream of material flowing through the magnetosphere of the white dwarf. The luminosity of the TeV source depends on the state of the system (flaring/quiet) and is limited to < 5x10^{29} erg/s. These results allow us to understand a lack of success in searching for the high-energy emission of AE Aqr with the Compton Gamma-ray Observatory and the Whipple Observatory.Comment: 8 pages, accepted for publication in A&

The mass function of nearby black hole candidates

The mass function of super-massive black holes in our cosmic neighborhood is required to understand the statistics of their activity and consequently the origin of the ultra high energy particles. We determine a mass function of black hole candidates from the entire sky except for the Galactic plane. Using the 2MASS catalogue as a starting point, and the well established correlation between black hole mass and the bulge of old population of stars, we derive a list of nearby black hole candidates within the redshift range z < 0.025, then do a further selection based on the Hubble-type, and give this as a catalogue elsewhere. The final list of black hole candidates above a mass of M_BH > 3*10^{6} M_sol has 5,829 entries; moreover doing a further Hubble type correction to account for the selection effects cuts down the number to 2,919 black hole candidates. We also correct for volume, so that this mass function is a volume limited distribution to redshift 0.025 The differential mass function of nearby black hole candidates is a curved function, with a straight simple power-law of index -3 above 10^{8} M_sol, growing progressively flatter towards lower masses, turning off towards a gap below 3*10^{6} M_sol, and then extending into the range where nuclear star clusters replace black holes. The shape of this mass function can be explained in a simple merger picture. Integrating this mass function over the redshift range, from which it has been derived, gives a total number of black holes with z 10^{7} M_sol of about 2.4*10^{4}, or, if we just average uniformly, 0.6 for every square degree on the sky. In different models many of these are candidates for ultra high energy particles sources. If a very small fraction of the super-massive black holes produces ultra high energy cosmic rays, this should be enough to observe the highly inhomogeneous distribution of the galaxies.Comment: 12 pages, 6 figures, resubmitted to A&