7178771
Gamma Rays from Ultra-High-Energy Cosmic Rays in Cygnus A
Ultra-high-energy cosmic rays (UHECRs) accelerated in the jets of active galactic nuclei can accumulate in high magnetic field, ~100 kpc-scale regions surrounding powerful radio galaxies. Photohadronic processes involving UHECRs and photons of the extragalactic background light make ultrarelativistic electrons and positrons that initiate electromagnetic cascades, leading to the production of a γ-ray synchrotron halo. We calculate the halo emission in the case of Cygnus A and show that it should be detectable with the Fermi Gamma-Ray Space Telescope and possibly detectable with ground-based γ-ray telescopes if radio galaxies are the sources of UHECRs.
14195601
The Hard VHE γ-Ray Emission in High-Redshift TeV Blazars: Comptonization of Cosmic Microwave Background Radiation in an Extended Jet?
Observations of very-high-energy (VHE; E > 250 GeV) γ-ray emission from several blazars at z > 0.1 have placed stringent constraints on the elusive spectrum and intensity of the intergalactic infrared background radiation (IIBR). Correcting the observed VHE spectrum for γγ absorption, even by the lowest plausible level of the IIBR, provides evidence for a very hard (photon spectral index Γph < 2) intrinsic source spectrum out to TeV energies. Such a hard VHE γ-ray spectrum poses a serious challenge to the conventional synchrotron self-Compton (SSC) interpretation of the VHE emission of TeV blazars and suggests the emergence of a separate emission component beyond a few hundred GeV. Here we propose that such a very hard, slowly variable VHE emission component in TeV blazars may be produced via Compton upscattering of cosmic microwave background (CMB) photons by shock-accelerated electrons in an extended jet. For the case of 1ES 1101–232, this component could dominate the bolometric luminosity of the extended jet if the magnetic fields are of the order of typical intergalactic magnetic fields (B ~ 10 μG) and if electrons are still being accelerated out to TeV energies (γ 4 × 106) on kiloparsec scales along the jet.
2202526
Transformation Properties of External Radiation Fields, Energy-Loss Rates and Scattered Spectra, and a Model for Blazar Variability
We treat transformation properties of external radiation fields in the proper frame of a plasma moving with constant speed. The specific spectral energy densities of external isotropic and accretion disk radiation fields are derived in the comoving frame of relativistic outflows, such as those thought to be found near black hole jet and gamma-ray burst sources. Nonthermal electrons and positrons Compton-scatter this radiation field, and high-energy protons and ions interact with this field through photomeson and photopair production. We revisit the problem of the Compton-scattered spectrum associated with an external accretion disk radiation field and clarify a past treatment by the authors. Simple expressions for energy-loss rates and Thomson-scattered spectra are given for ambient soft photon fields consisting of either a surrounding external isotropic monochromatic radiation field or an azimuthally symmetric, geometrically thin accretion disk radiation field. A model for blazar emission is presented that displays a characteristic spectral and variability behavior due to the presence of a direct accretion disk component. The disk component and distinct flaring behavior can be bright enough to be detected from flat-spectrum radio quasars with GLAST. Spectral states of blazars are characterized by the relative importance of the accretion disk and scattered radiation fields and, in the extended jet, by the accretion disk, inner jet, and cosmic microwave background radiation fields.
51800388
Models of Very-High-Energy Gamma-Ray Emission from the Jets of Microquasars: Orbital Modulation
The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST mission.
16506995
Is the High-Energy Emission from Centaurus A Compton-Scattered Jet Radiation?
Abstract : We consider whether the hard X-ray and soft gamma-ray emission from Centaurus A is beamed radiation from the active nucleus which is Compton-scattered into our line-of-sight. We derive the spectrum and degree of polarization of scattered radiation when incident beamed radiation is scattered from a cold (kappa Tau << mec2) electron cloud moving with bulk relativistic motion along the jet axis, and calculate results for an unpolarized, highly-beamed incident power-law photon source. The spectra of the scattered radiation exhibit a cut-off at gamma-ray energies due to electron recoil. The cut off energy depends on the observer's viewing angle and the bulk Lorentz factor of the scattering medium. We fit the OSSE data from Centaurus A with this model and find that if the scatterers are not moving relativistically, then the angle the jet makes with respect to our line-of-sight is 61 degrees plus or minus 5 degrees. We predict a high degree of polarization of the scattered radiation below ~300 keV. Future measurements with X-ray and gamma-ray polarimeters could be used to constrain or rule out such a scenario.
119370236
A Class of Exact Solution to the Blandford-Znajek Process
We analyze the constraint equation giving allowed solutions describing fields and currents in a force-free magnetosphere around a rotating black hole. Utilizing the divergence properties of the energy and angular-momentum fluxes for physically allowed solutions, we conclude that poloidal surfaces are independent of the radial coordinate for large values of $r$. Using this fact and the Znajek regularity condition, we explicitly derive all possible exact solutions admitted by the constraint equation for $r$ independent poloidal surfaces, which are given in terms of the electromagnetic angular velocity function $\Omega = 1/a\sin^2\theta$, where $a$ is the angular momentum per unit mass of the black hole.
18301162
Off-shell effects in dilepton production from hot interacting mesons
The production of dielectrons in reactions involving a{sub 1} mesons and pions is studied. We compare results obtained with different phenomenological Lagrangians that have been used in connection with hadronic matter and finite nuclei. We insist on the necessity for those interactions to satisfy known empirical properties of the strong interaction. Large off-shell effects in dielectron production are found and some consequences for the interpretation of heavy ion data are outlined. We also compare with results obtained using experimentally extracted spectral functions. {copyright} {ital 1998} {ital The American Physical Society}