31 research outputs found
IceCube expectations for two high-energy neutrino production models at active galactic nuclei
We have determined the currently allowed regions of the parameter spaces of
two representative models of diffuse neutrino flux from active galactic nuclei
(AGN): one by Koers & Tinyakov (KT) and another by Becker & Biermann (BB). Our
observable has been the number of upgoing muon-neutrinos expected in the
86-string IceCube detector, after 5 years of exposure, in the range 10^5 <
E/GeV < 10^8. We have used the latest estimated discovery potential of the
IceCube-86 array at the 5-sigma level to determine the lower boundary of the
regions, while for the upper boundary we have used either the AMANDA upper
bound on the neutrino flux or the more recent preliminary upper bound given by
the half-completed IceCube-40 array (IC40). We have varied the spectral index
of the proposed power-law fluxes, alpha, and two parameters of the BB model:
the ratio between the boost factors of neutrinos and cosmic rays,
Gamma_nu/Gamma_{CR}, and the maximum redshift of the sources that contribute to
the cosmic-ray flux, zCRmax. For the KT model, we have considered two
scenarios: one in which the number density of AGN does not evolve with redshift
and another in which it evolves strongly, following the star formation rate.
Using the IC40 upper bound, we have found that the models are visible in
IceCube-86 only inside very thin strips of parameter space and that both of
them are discarded at the preferred value of alpha = 2.7 obtained from fits to
cosmic-ray data. Lower values of alpha, notably the values 2.0 and 2.3 proposed
in the literature, fare better. In addition, we have analysed the capacity of
IceCube-86 to discriminate between the models within the small regions of
parameter space where both of them give testable predictions. Within these
regions, discrimination at the 5-sigma level or more is guaranteed.Comment: 24 pages, 6 figures, v2: new IceCube-40 astrophysical neutrino upper
bound and IceCube-86 discovery potential used, explanation of AGN flux models
improved, only upgoing neutrinos used, conclusions strengthened. Accepted for
publication in JCA
Can a wormhole generate electromagnetic field?
We have considered the possibility of a slowly rotating wormhole surrounded
by a cloud of charged particles. Due to slow rotation of the wormhole, the
charged particles are dragged thereby producing an electromagnetic field. We
have determined the strength of this electromagnetic field and the
corresponding flux of radiation.Comment: 9 pages, typos fixe
Probing the innermost regions of AGN jets and their magnetic fields with radioastron. I. Imaging BL LACERTAE at 21 μm as resolution
We present the first polarimetric space very long baseline interferometry (VLBI) imaging observations at 22 GHz. BL Lacertae was observed in 2013 November 10 with the RadioAstron space VLBI mission, including a ground array of 15 radio telescopes. The instrumental polarization of the space radio telescope is found to be less than 9%, demonstrating the polarimetric imaging capabilities of RadioAstron at 22 GHz. Ground-space fringes were obtained up to a projected baseline distance of 7.9 Earth diameters in length, allowing us to image the jet in BL Lacertae with a maximum angular resolution of 21 μas, the highest achieved to date. We find evidence for emission upstream of the radio core, which may correspond to a recollimation shock at about 40 μas from the jet apex, in a pattern that includes other recollimation shocks at approximately 100 and 250 μas from the jet apex. Polarized emission is detected in two components within the innermost 0.5 mas from the core, as well as in some knots 3 mas downstream. Faraday rotation analysis, obtained from combining RadioAstron 22 GHz and ground-based 15 and 43 GHz images, shows a gradient in rotation measure and Faraday-corrected polarization vector as a function of position angle with respect to the core, suggesting that the jet in BL Lacertae is threaded by a helical magnetic field. The intrinsic de-boosted brightness temperature in the unresolved core exceeds K, suggesting, at the very least, departure from equipartition of energy between the magnetic field and radiating particles.This research has been supported by the Spanish Ministry of Economy and Competitiveness grant AYA2013-40825-P, by the Russian Foundation for Basic Research (projects 13-02-12103, 14-02-31789, and 15-02-00949), and St. Petersburg University research grant 6.38.335.2015. The research at Boston University (BU) was funded in part by NASA Fermi Guest Investigator grant NNX14AQ58G. Y.M. acknowledges support from the ERC Synergy Grant >BlackHoleCam-Imaging the Event Horizon of Black Holes> (Grant 610058). Part of this work was supported by the COST Action MP1104 >Polarization as a tool to study the Solar System and beyond.> The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the Russian Federal Space Agency, in collaboration with partner organizations in Russia and other countries.Peer Reviewe
Electromagnetic Fields and Charged Particle Motion Around Magnetized Wormholes
We perform a study to describe motion of charged particles under the
influence of electromagnetic and gravitational fields of a slowly rotating
wormhole with nonvanishing magnetic moment. We present analytic expression for
potentials of electromagnetic field for an axially symmetric slowly rotating
magnetized wormholes. While addressing important issues regarding the subject,
we compare our results of motion around black holes and wormholes in terms of
the ratio of radii of event horizons of a black hole and of the throat of a
wormhole. It is shown that both radial and circular motions of test bodies in
the vicinity of a magnetized wormhole could give rise to a peculiar
observational astrophysical phenomenon.Comment: 9 pages, 4 figures, 2 tables, accepted for publication in
Astrophysics & Space Scienc
Compact jets as probes for sub-parsec scale regions in AGN
Compact relativistic jets in active galactic nuclei offer an effective tool
for investigating the physics of nuclear regions in galaxies. The emission
properties, dynamics, and evolution of jets in AGN are closely connected to the
characteristics of the central supermassive black hole, accretion disk and
broad-line region in active galaxies. Recent results from studies of the
nuclear regions in several active galaxies with prominent outflows are reviewed
in this contribution.Comment: AASLaTeX, 5 pages, 4 figures. Accepted in Astrophysics and Space
Scienc
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Constraining the electric charges of some astronomical bodies in Reissner-Nordstrom spacetimes and generic r^-2-type power-law potentials from orbital motions
We put model-independent, dynamical constraints on the net electric charge Q
of some astronomical and astrophysical objects by assuming that their exterior
spacetimes are described by the Reissner-Nordstroem metric, which induces an
additional potential U_RN \propto Q^2 r^-2. Our results extend to other
hypothetical power-law interactions inducing extra-potentials U_pert = r^-2 as
well (abridged).Comment: LaTex2e, 16 pages, 3 figures, no tables, 128 references. Version
matching the one at press in General Relativity and Gravitation (GRG). arXiv
admin note: substantial text overlap with arXiv:1112.351