Extragalactic neutrino background from very young pulsars surrounded by supernova envelopes

We estimate the extragalactic muon neutrino background which is produced by hadrons injected by very young pulsars at an early phase after supernova explosion. It is assumed that hadrons are accelerated in the pulsar wind zone which is filled with thermal photons captured below the expanding supernova envelope. In collisions with those thermal photons hadrons produce pions which decay into muon neutrinos. At a later time, muon neutrinos are also produced by the hadrons in collisions with matter of the expanding envelope. We show that extragalactic neutrino background predicted by such a model should be detectable by the planned 1 km$^2$ neutrino detector if a significant part of pulsars is born with periods shorter than $\sim 10$ ms. Since such population of pulsars is postulated by the recent models of production of extremely high energy cosmic rays, detection of neutrinos with predicted fluxes can be used as their observational test.Comment: 4 pages, 2 figures, A&A style, accepted to A&A Let

Gamma-ray production in young open clusters: Berk 87, Cyg OB2 and Westerlund 2

Young open clusters are likely sites of cosmic ray acceleration as indicated by recent detections of the TeV gamma-ray sources in the directions of two open clusters (Cyg OB2 and Westerlund 2) and their directional proximity to some unidentified EGRET sources. In fact, up to now a few different scenarios for acceleration of particles inside open clusters have been considered, i.e. shocks in massive star winds, pulsars and their nebulae, supernova shocks, massive compact binaries. Here we consider in detail the radiation processes due to both electrons and hadrons accelerated inside the open cluster. As a specific scenario, we apply the acceleration process at the shocks arising in the winds of WR type stars. Particles diffuse through the medium of the open cluster during the activity time of the acceleration scenario defined by the age of the WR star. They interact with the matter and radiation, at first inside the open cluster and, later in the dense surrounding clouds. We calculate the broad band spectrum in different processes for three example open clusters (Berk 87, Cyg OB2, Westerlund 2) for which the best observational constraints on the spectra are at present available. It is assumed that the high energy phenomena, observed from the X-ray up to the GeV-TeV gamma-ray energies, are related to each other. We conclude that the most likely description of the radiation processes in these objects is achieved in the hybrid (leptonic-hadronic) model in which leptons are responsible for the observed X-ray and GeV gamma-ray emission and hadrons are responsible for the TeV gamma-ray emission, which is produced directly inside and in dense clouds surrounding the open cluster.Comment: 12 pages, 7 figures, accepted to MNRA

TeV neutrinos from microquasars in compact massive binaries

We consider a compact binary system in which a Wolf-Rayet star supplies matter onto a stellar mass black hole or a neutron star. This matter forms an accretion disk which ejects a jet as observed in Galactic microquasars. A part of the jet kinetic energy, typically 10%, can be transfered to relativistic nuclei. These nuclei lose nucleons as a result of photo-disintegration process in collisions with thermal photons from the accretion disk and the massive star. Due to the head on photon-nucleus collisions most of neutrons released from nuclei move towards the surface of the accretion disk and/or the massive star producing neutrinos in collisions with the matter. We calculate the spectra of muon neutrinos and expected neutrino event rates in a 1 km^2 neutrino detector of the IceCube type from a microquasar inside our Galaxy applying, as an example, the parameters of the Cyg X-3 binary system, provided that nuclei are accelerated to the Lorentz factors above 10^6 with the power law spectrum with an index close to 2.Comment: 13 pages, 2 figures, ApJ, accepte

Modulated Gamma-ray emission from compact millisecond pulsar binary systems

A significant amount of the millisecond pulsars has been discovered within binary systems. In several such binary systems the masses of the companion stars have been derived allowing to distinguish two classes of objects, called the Black Widow and the Redback binaries. Pulsars in these binary systems are expected to produce winds which, colliding with stellar winds, create conditions for acceleration of electrons. These electrons should interact with the anisotropic radiation from the companion stars producing gamma-ray emission modulated with the orbital period of the binary system. We consider the interaction of a millisecond pulsar (MSP) wind with a very inhomogeneous stellar wind from the companion star within binary systems of the Black Widow and Redback types. It is expected that the pulsar wind should mix efficiently with the inhomogeneous stellar wind. Electrons accelerated in such mixed, turbulent winds can interact with the magnetic field and also strong radiation from the companion star producing not only synchrotron radiation but also gamma-rays in the the Inverse Compton process. Applying numerical methods, we calculated the GeV-TeV gamma-ray spectra and the light curves expected from some millisecond pulsar binary systems. It is concluded that energetic millisecond pulsar binary systems create a new class of TeV gamma-ray sources which could be detectable by the future Cherenkov arrays (e.g. CTA) and possibly also by the extensive campaigns with the present arrays (HESS, MAGIC, VERITAS). However, gamma-ray emission from the millisecond pulsar binary systems is predicted to have different features than those observed in the case of massive TeV gamma-ray binaries such as LS I 303 61 or LS 5039. The maximum in the TeV gamma-ray orbital light curve should appear when the MSP is behind the companion star.Comment: 10 pages, 4 figures, 1 table, accepted to Astronomy and Astrophysic

Gamma-rays from the vicinity of accreting neutron stars inside compact high-mass X-ray binaries

Dense wind of a massive star can be partially captured by a neutron star (NS) inside a compact binary system. Depending on the parameters of NS and the wind, the matter can penetrate the inner NS magnetosphere. At some distance from the NS a very turbulent and magnetized transition region is formed due to the balance between the magnetic pressure and the pressure inserted by accreting matter. This region provides good conditions for acceleration of particles to relativistic energies. The matter at the transition region can farther accrete onto the NS surface (the accretor phase) or is expelled from the NS vicinity (the propeller phase). We consider the consequences of acceleration of electrons at the transition region concentrating on the situation in which at least part of the matter falls onto the NS surface. This matter creates a hot spot on the NS surface which emits thermal radiation. Relativistic electrons lose energy on the synchrotron process and the inverse Compton (IC) scattering of this thermal radiation. We calculate the synchrotron spectra (from X-rays to soft $\gamma$-rays) and IC spectra (above a few tens MeV) expected in such a scenario. It is argued that a population of recently discovered massive binaries by the INTEGRAL observatory, which contain neutron stars hidden inside dense stellar winds of massive stars, can be detectable by the recently launched {\it Fermi} LAT telescope at GeV energy range. As an example, we predict the expected $\gamma$-ray flux from recently discovered source IGR J19140+0951.Comment: 13 pages, 9 figures, revised version submitted to A&