266 research outputs found
Angular, spectral, and time distributions of highest energy protons and associated secondary gamma-rays and neutrinos propagating through extragalactic magnetic and radiation fields
The angular, spectral and temporal features of the highest energy protons and
accompanying them secondary neutrinos and synchrotron gamma-rays propagating
through the intergalactic magnetic and radiation fields are studied using the
analytical solutions of the Boltzmann transport equation obtained in the limit
of the small-angle and continuous-energy-loss approximation.Comment: 21 pages, 13 figure
Energy spectra of gamma-rays, electrons and neutrinos produced at proton-proton interactions in the very high energy regime
We present new parametrisations of energy spectra of secondary particles, -mesons, gamma-rays, electrons and neutrinos, produced in inelastic proton-proton collisions. The simple analytical approximations based on imulations of proton-proton interactions using the public available SIBYLL code, provide very good accuracy for energy distributions of secondary products in the energy range above 100 GeV. Generally, the recommended analytical formulae deviate from the simulated distributions within a few percent over a large range of - the fraction of energy of the incident proton transferred to the secondaries. Finally, we describe an approximate procedure of continuation of calculations towards low energies, down to the threshold of -meson production
Fermi~I particle acceleration in converging flows mediated by magnetic reconnection
Context. Converging flows with strong magnetic fields of different polarity
can accelerate particles through magnetic reconnection. If the particle mean
free path is longer than the reconnection layer is thick, but much shorter than
the entire reconnection structure, the particle will mostly interact with the
incoming flows potentially with a very low escape probability. Aims. We
explore, in general and also in some specific scenarios, the possibility of
particles to be accelerated in a magnetic reconnection layer by interacting
only with the incoming flows. Methods. We characterize converging flows that
undergo magnetic reconnection, and derive analytical estimates for the particle
energy distribution, acceleration rate, and maximum energies achievable in
these flows. We also discuss a scenario, based on jets dominated by magnetic
fields of changing polarity, in which this mechanism may operate. Results. The
proposed acceleration mechanism operates if the reconnection layer is much
thinner than its transversal characteristic size, and the magnetic field has a
disordered component. Synchrotron losses may prevent electrons from entering in
this acceleration regime. The acceleration rate should be faster, and the
energy distribution of particles harder than in standard diffusive shock
acceleration. The interaction of obstacles with the innermost region of jets in
active galactic nuclei and microquasars may be suitable sites for particle
acceleration in converging flows.Comment: 4 pages, 2 figures, Reserch Note, in press, A&A (final version
Gamma-ray emission from massive young stellar objects
Massive stars form in dense and massive molecular cores. The exact formation
mechanism is unclear, but it is possible that some massive stars are formed by
processes similar to those that produce the low-mass stars, with
accretion/ejection phenomena occurring at some point of the evolution of the
protostar. This picture seems to be supported by the detection of a collimated
stellar wind emanating from the massive protostar IRAS 16547-4247. A triple
radio source is associated with the protostar: a compact core and two radio
lobes. The emission of the southern lobe is clearly non-thermal. Such emission
is interpreted as synchrotron radiation produced by relativistic electrons
locally accelerated at the termination point of a thermal jet. Since the
ambient medium is determined by the properties of the molecular cloud in which
the whole system is embedded, we can expect high densities of particles and
infrared photons. Because of the confirmed presence of relativistic electrons,
inverse Compton and relativistic Bremsstrahlung interactions are unavoidable.
Proton-proton collision should also occur, producing an injection of neutral
pions. In this paper we aim at making quantitative predictions of the spectral
energy distribution of the non-thermal spots generated by massive young stellar
objects, with emphasis on the particular case of IRAS 16547-4247. We present
spectral energy distributions for the southern lobe of this source, for a
variety of conditions. We show that high-energy emission might be detectable
from this object in the gamma-ray domain (MeV to TeV). The source may also be
detectable at X-rays through long exposures with current X-ray instruments.Comment: 8 pages, 6 figures, accepted for publication in A&
Electroproduction of electron-positron pair in a medium
The process of electron-positron pair creation by a high-energy electron in a
medium is analyzed. The spectral distribution over energies of created
particles is calculated for the direct and cascade mechanisms of the process.
The Coulomb corrections are included. The new formulation of the equivalent
photons method is developed which takes into account the influence of multiple
scattering. It is shown the effects of multiple scattering can be quite
effectively studied in the process under consideration.Comment: 10 pages, 4 figure
Rapid TeV variability in Blazars as result of Jet-Star Interaction
We propose a new model for the description of ultra-short flares from TeV
blazars by compact magnetized condensations (blobs), produced when red giant
stars cross the jet close to the central black hole. Our study includes a
simple dynamical model for the evolution of the envelope lost by the star in
the jet, and its high energy nonthermal emission through different leptonic and
hadronic radiation mechanisms. We show that the fragmented envelope of the star
can be accelerated to Lorentz factors up to 100 and radiate effectively the
available energy in gamma-rays predominantly through proton synchrotron
radiation or external inverse Compton scattering of electrons. The model can
readily explain the minute-scale TeV flares on top of longer (typical
time-scales of days) gamma-ray variability as observed from the blazar PKS
2155-304. In the framework of the proposed scenario, the key parameters of the
source are robustly constrained. In the case of proton synchrotron origin of
the emission a mass of the central black hole of , a total jet power of and a Doppler factor, of the gamma-ray emitting blobs, of
are required. Whilst for the external inverse Compton model,
parameters of
, and the are required.Comment: 25 pages, 11 figures, Submitted to Ap
Geant4 simulation of production and interaction of muons
A set of models for Monte Carlo simulation of production and interaction of high energy muons is developed in the framework of the Geant4 toolkit. It describes the following physics processes: ionization of high energy muons with radiative corrections, bremsstrahlung, electron-positron pair production, muon induced nuclear reactions, gamma annihilation into muon pair, positron annihilation into muon pair, and into pion pair. These processes are essential for the LHC experiments, for the understanding of the background in underground detectors, for the simulation of effects related with high-energy muons in cosmic ray experiments and for the estimation of backgrounds in future colliders. The applicability area of the models extends to 1 PeV. The major use-cases are discussed
Restricting UHECRs and cosmogenic neutrinos with Fermi-LAT
Ultrahigh energy cosmic ray (UHECR) protons interacting with the cosmic
microwave background (CMB) produce UHE electrons and gamma-rays that in turn
initiate electromagnetic cascades on CMB and infrared photons. As a result, a
background of diffuse isotropic gamma radiation is accumulated in the energy
range E\lsim 100 GeV. The Fermi-LAT collaboration has recently reported a
measurement of the extragalactic diffuse background finding it less intense and
softer than previously measured by EGRET. We show that this new result
constrains UHECR models and the flux of cosmogenic neutrinos. In particular, it
excludes models with cosmogenic neutrino fluxes detectable by existing neutrino
experiments, while next-generation detectors as e.g. JEM-EUSO can observe
neutrinos only for extreme parameters.Comment: 7 pages, 6 eps figures; v2: minor changes, v3: final version, added
discussion of EGMF influenc
High-energy emission from jet-clump interactions in microquasars
High-mass microquasars are binary systems consisting of a massive star and an
accreting compact object from which relativistic jets are launched. There is
considerable observational evidence that winds of massive stars are clumpy.
Individual clumps may interact with the jets in high-mass microquasars to
produce outbursts of high-energy emission. Gamma-ray flares have been detected
in some high-mass X-ray binaries, such as Cygnus X-1, and probably in LS 5039
and LS I+61 303. We predict the high-energy emission produced by the
interaction between a jet and a clump of the stellar wind in a high-mass
microquasar. Assuming a hydrodynamic scenario for the jet-clump interaction, we
calculate the spectral energy distributions produced by the dominant
non-thermal processes: relativistic bremsstrahlung, synchrotron and inverse
Compton radiation, for leptons, and for hadrons, proton-proton collisions.
Significant levels of emission in X-rays (synchrotron), high-energy gamma rays
(inverse Compton), and very high-energy gamma rays (from the decay of neutral
pions) are predicted, with luminosities in the different domains in the range ~
10^{32}-10^{35} erg/s. The spectral energy distributions vary strongly
depending on the specific conditions. Jet-clump interactions may be detectable
at high and very high energies, and provide an explanation for the fast TeV
variability found in some high-mass X-ray binary systems.
Our model can help to infer information about the properties of jets and
clumpy winds by means of high-sensitivity gamma-ray astronomy.Comment: Accepted for publication in A&A (10 pages, 8 figures
Gamma-ray absorption and the origin of the gamma-ray flare in Cygnus X-1
The high-mass microquasar Cygnus X-1, the best-established candidate for a
stellar-mass black hole in the Galaxy, has been detected in a flaring state at
very high energies (VHE), E > 200 GeV, by the Atmospheric Cherenkov Telescope
MAGIC. The flare occurred at orbital phase 0.91, where phase 1 is the
configuration with the black hole behind the companion high-mass star, when the
absorption of gamma-ray photons by photon-photon annihilation with the stellar
field is expected to be highest. We aim to set up a model for the high-energy
emission and absorption in Cyg X-1 that can explain the nature of the observed
gamma-ray flare. We study the gamma-ray opacity due to pair creation along the
whole orbit, and for different locations of the emitter. Then we consider a
possible mechanism for the production of the VHE emission. We present detailed
calculations of the gamma-ray opacity and infer from these calculations the
distance from the black hole where the emitting region was located. We suggest
that the flare was the result of a jet-clump interaction where the decay
products of inelastic proton-proton collisions dominate the VHE outcome. We are
able to reproduce the spectrum of Cyg X-1 during the observed flare under
reasonable assumptions. The flare may be the first event of jet-cloud
interaction ever detected at such high energies.Comment: 9 pages, 7 figure
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