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&

VLBI radio structure and radio brightening of the high-energy neutrino emitting blazar TXS 0506+056

We report on the radio brightening of the blazar TXS 0506+056 (at $z=0.3365$), supporting its identification as source of the high-energy (HE) neutrino IC-170922A by the IceCube Neutrino Observatory. MOJAVE/VLBA data indicate its radio brightness abruptly increasing since January 2016. When decomposing the total radio flux density curve (January 2008 - July 2018) provided by the Owens Valley Radio Observatory into eight Gaussian flares, the peak time of the largest flare overlaps with the HE neutrino detection, while the total flux density exhibits a threefold increase since January 2016. We reveal the radio structure of TXS 0506+056 by analysing VLBI data from the MOJAVE/VLBA Survey. The jet-components maintain quasi-stationary core separations. The structure of the ridge line is indicative of a jet curve at the region $0.5\div2$ mas ($2.5\div9.9$ pc projected) from the VLBI core. The brightness temperature of the core and the pc-scale radio morphology support a helical jet structure at small inclination angle ($<8.2^{\circ}$). The jet pointing towards the Earth is key property facilitating multimessenger observations (HE neutrinos, $\gamma$- and radio flares). The radio brightening preceding the detection of a HE neutrino is similar to the one reported for the blazar PKS 0723--008 and IceCube event ID5.Comment: 5 pages, 3 tables, 4 figures, accepted to MNRAS Letter

TeV Cherenkov Events as Bose-Einstein Gamma Condensations

The recent detection of gamma radiation from Mkn 501 at energies as high as 25 TeV suggests stringent upper bounds on the diffuse, far infrared, extragalactic radiation density. The production of electron-positron pairs through photon-photon collisions would prevent gamma photons of substantially higher energies from reaching us across distances of order 100 Mpc. However, coherently arriving TeV or sub-TeV gammas - Bose-Einstein condensations of photons at these energies - could mimic the Cherenkov shower signatures of extremely energetic gammas. To better understand such events, we describe their observational traits and discuss how they might be generated.Comment: 12 pages, 2 figures, accepted for publication in Ap.J.(Lett.