173 research outputs found
Supernova remnants as cosmic ray accelerators. SNR IC 443
We examine the hypothesis that some supernova remnants (SNRs) may be
responsible for some unidentified gamma-ray sources detected by EGRET
instrument aboard the Compton Gamma Ray Observatory. If this is the case,
gamma-rays are produced via pion production and decay from direct inelastic
collisions of accelerated by SNR shock wave ultrarelativistic protons with
target protons of the interstellar medium. We develop a 3-D hydrodynamical
model of SNR IC 443 as a possible cosmic gamma-ray source 2EG J0618+2234. The
derived parameters of IC 443: the explosion energy E_o=2.7*10^{50} erg, the
initial hydrogen number density n(0)=0.21 cm^{-3}, the mean radius R=9.6 pc and
the age t=4500 yr result in too low gamma-ray flux, mainly because of the low
explosion energy. Therefore, we investigate in detail the hydrodynamics of IC
443 interaction with a nearby massive molecular cloud and show that the reverse
shock wave considerably increases the cosmic ray density in the interaction
region. Meantime, the Rayleigh-Taylor instability of contact discontinuity
between the SNR and the cloud provides an effective mixing of the containing
cosmic ray plasma and the cloud material. We show that the resulting gamma-ray
flux is consistent with the observational data.Comment: Printed in Condenced Matter Physic
High-energy and very high-energy gamma-ray emission from the magnetar SGR 1900+14 neighbourhood
Magnetar wind nebulae (MWNe), created by new-born millisecond magnetars, and
magnetar giant flares are PeVatron candidates and even potential sources of
ultra high energy () cosmic rays (UHECRs). Nonthermal
high-energy (HE, ) and very high-energy (VHE, ) -ray emission from magnetars' neighbourhoods should be
a promising signature of acceleration processes. We investigate a possibility
of explaining HE and VHE -ray emission from the vicinity of the
magnetar SGR 1900+14 by cosmic rays accelerated in a Supernova remnant of a
magnetar-related Supernova and/or in a MWN. Simulation of the observed HE (the
extended Fermi-LAT source 4FGL J1908.6+0915e) and VHE (the extended H.E.S.S.
source candidate HOTS J1907+091 and the point-like HAWC TeV source 3HWC
J1907+085) -ray emission, spatially coincident with the magnetar SGR
1900+14, was carried out in the framework of hadronic (pp collisions with a
subsequent pion decay) and leptonic (inverse Compton scattering of low energy
background photons by ultrarelativistic electrons) models. We show that under
reasonable assumptions about parameters of the circumstellar medium the
observed -ray emission of Fermi-LAT 4FGL J1908.6+0915e, H.E.S.S.
HOTSJ1907+091 and 3HWC J1907+085 sources may be explained or at least
considerably contributed by a (still undetected) magnetar-connected Hypernova
remnant and/or a MWN created by new-born millisecond magnetar with a large
reserve of rotational energy .Comment: 13 pages, 7 figure
Supernova remnants as cosmic ray accelerators: SNR IC 443
We examine the hypothesis that some supernova remnants (SNRs) may be responsible for some unidentified gamma-ray sources detected by EGRET instrument aboard the Compton Gamma Ray Observatory. If this is the case, gamma-rays are produced via pion production and decay from direct inelastic collisions of accelerated by SNR shock wave ultrarelativistic protons with target protons of the interstellar medium. We develop a 3-D hydrodynamical model of SNR IC 443 as a possible cosmic gamma-ray source 2EG J0618+2234. The derived parameters of IC 443: the explosion energy E_o=2.7*10^{50} erg, the initial hydrogen number density n(0)=0.21 cm^{-3}, the mean radius R=9.6 pc and the age t=4500 yr result in too low gamma-ray flux, mainly because of the low explosion energy. Therefore, we investigate in detail the hydrodynamics of IC 443 interaction with a nearby massive molecular cloud and show that the reverse shock wave considerably increases the cosmic ray density in the interaction region. Meantime, the Rayleigh-Taylor instability of contact discontinuity between the SNR and the cloud provides an effective mixing of the containing cosmic ray plasma and the cloud material. We show that the resulting gamma-ray flux is consistent with the observational data
A dip in the UHECR spectrum and the transition from galactic to extragalactic cosmic rays
The dip is a feature in the diffuse spectrum of ultra-high energy (UHE)
protons caused by electron-positron pair production on the cosmic microwave
background (CMB) radiation. For a power-law generation spectrum , the
calculated position and shape of the dip is confirmed with high accuracy by the
spectra observed by the Akeno-AGASA, HiRes, Yakutsk and Fly's Eye detectors.
When the particle energies, measured in these detectors, are calibrated by the
dip, their fluxes agree with a remarkable accuracy. The predicted shape of the
dip is quite robust. The dip is only modified strongly when the fraction of
nuclei heavier than protons is high at injection, which imposes some
restrictions on the mechanisms of acceleration operating in UHECR sources. The
existence of the dip, confirmed by observations, implies that the transition
from galactic to extragalactic cosmic rays occurs at E \lsim 1\times 10^{18}
eV. We show that at energies lower than a characteristic value eV, the spectrum of extragalactic cosmic rays
flattens in all cases of interest, and it provides a natural transition to a
steeper galactic cosmic ray spectrum. This transition occurs at some energy
below , corresponding to the position of the so-called second knee.
We discuss extensively the constraints on this model imposed by current
knowledge of acceleration processes and sources of UHECR and compare it with
the traditional model of transition at the ankle.Comment: Version Accepted for Publication in Astroparticle Physics (minor
changes
Propagation of different components of cosmic rays from Centaurus A in the Galactic magnetic fields
Propagation of different chemical composition ultrahigh energy cosmic rays in the galactic magnetic fields was simulated. The simulation for the ultra high energy events, registered by the AUGER observatory in the sky region near Centaurus A was performed. It is shown that some of these events could originate from Centaurus A
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