203 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
Modeling of the Radio Emission from the Vela Supernova Remnant
Supernova remnants (SNRs) are widely considered to be sites of Galactic
cosmic ray (CR) acceleration. Vela is one of the nearest Galactic composite
SNRs to Earth accompanied by the Vela pulsar and its pulsar wind nebula (PWN)
Vela X. The Vela SNR is one of the most studied remnants and it benefits from
precise estimates of various physical parameters such as distance and age.
Therefore, it is a perfect object for a detailed study of physical processes in
SNRs. The Vela SNR expands into the highly inhomogeneous cloudy interstellar
medium (ISM) and its dynamics is determined by the heating and evaporation of
ISM clouds. It features an asymmetrical X-ray morphology which is explained by
the expansion into two media with different densities. This could occur if the
progenitor of the Vela SNR exploded close to the edge of the stellar wind
bubble of the nearby Wolf-Rayet star Velorum and hence one part of
the remnant expands into the bubble. The interaction of the ejecta and the main
shock of the remnant with ISM clouds causes formation of secondary shocks at
which additional particle acceleration takes place. This may lead to the close
to uniform distribution of relativistic particles inside the remnant. We
calculate the synchrotron radio emission within the framework of the new
hydrodynamical model which assumes the supernova explosion at the edge of the
stellar wind bubble. The simulated radio emission agrees well with both the
total radio flux from the remnant and the complicated radio morphology of the
source.Comment: 8 pages, 5 figures, 2 tables, accepted for publication in A&
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
Search for ultra high energy cosmic rays from radiogalaxy Virgo A
Active galactic nuclei (AGNs) are considered to be one of the most
appropriate sources of ultra high energy cosmic rays (UHECRs, ). Radiogalaxy Virgo A (M87) in the centre of a cluster of
galaxies Virgo Cluster (VC) can be a prominent source of UHECRs. We investigate
the possible contribution of Virgo A and the VC to the flux of events with
trans-GZK energies - extremely high energy cosmic rays (EHECRs) - from the
recent Auger and Telescope Array (TA) data sets ( and , respectively). We simulate EHECR propagation from Virgo A
and the VC taking into account their deflections in galactic (GMF) and
extragalactic (EGMF) magnetic fields and show that there is no excess of EHECR
arrival directions from images of Virgo A/VC at different EHECR rigidities. By
means of event-by-event analysis we recover the extragalactic arrival
directions of EHECR events detected by Auger and TA for representative set of
nuclei H(p), He, N, Si, Fe, and find evidences of enhanced fluxes of N-Si-Fe
EHECRs from the Local Filament and Hot/Cold Spot regions. The Local Filament
with its enhanced magnetic field is an expected contributor to the UHECR flux
as the closest to the Earth last scattering centre, whereas Hot/Cold Spot
region is a part of a larger arc-like spot, possibly created by diffusively
spreading jet of UHECRs, accelerated in the relativistic jet of Virgo A during
a prominent nuclear outburst about 10 - 12 Myr ago.Comment: This article has been accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
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
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
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