2,496 research outputs found
Detection of diffuse gamma-ray emission near the young massive cluster NGC 3603
We report the Fermi Large Area Telescope's detection of extended gamma-ray
emission towards the direction of the young massive star cluster NGC 3603. The
emission shows a hard spectrum with a photon index of 2.3 from 1 GeV to 250
GeV. The large size and high luminosity of this structure make it unlikely a
pulsar wind nebular. On the other hand the spatial correlation with the ionised
gas indicate a hadronic origin. The total cosmic ray (CR) protons energy are
estimated to be of the order assuming the gamma-ray are
produced in the interaction of CRs with ambient gas . The environment and
spectral features show significant similarity with the Cygnus cocoon. It
reveals that the young star clusters may be a gamma-ray source population and
they can potentially accelerate a significant fraction of the Galactic cosmic
rays.Comment: 6 pages, 5 figures, submitted to A&
Interpretation of the excess of antiparticles within a modified paradigm of galactic cosmic rays
We argue that the anomalously high fluxes of positrons and antiprotons found
in cosmic rays (CR) can be satisfactorily explained by introducing two
additional elements to the current "standard" paradigm of Galactic CRs. First,
we propose that the antiparticles are effectively produced in interactions of
primary CRs with the surrounding gas not only in the interstellar medium (ISM)
but also inside the accelerators. Secondly, we postulate the existence of two
source populations injecting CRs into the ISM with different, (1) soft (close
to ) and (2) hard ( or harder),
energy distributions. Assuming that CRs in the 2nd population of accelerators
accumulate "grammage" of the order of before their leakage
into ISM, we can explain the energy distributions and absolute fluxes of both
positrons and antiprotons, as well as the fluxes of secondary nuclei of the
(Li,Be,B) group. The superposition of contributions of two source populations
also explains the reported hardening of the spectra of CR protons and nuclei
above 200 GV. The 2nd source population accelerating CRs with a rate at the
level below 10 percent of the power of the 1st source population, can be
responsible for the highest energy protons and nuclei of Galactic CRs up to the
"knee" around .Comment: accepted for publication in PR
On the shape of the gamma-ray spectrum around the "-bump"
The "pion-decay" bump is a distinct signature of the differential energy
spectrum of -rays between 100 MeV and 1 GeV produced in hadronic
interactions of accelerated particles (cosmic rays) with the ambient gas. We
use the recent parametrisations of relevant cross-sections to study the
formation of the "pion-decay" bump. The -ray spectrum below the maximum
of this spectral feature can be distorted because of contributions of
additional radiation components, in particular, due to the bremsstrahlung of
secondary electrons and positrons, the products of decays of -mesons,
accompanying the -production. At energies below 100 MeV, a
non-negligible fraction of -ray flux could originate from interactions
of sub-relativistic heavy ions. We study the impact of these radiation channels
on the formation of the overall -ray spectrum based on a time-dependent
treatment of evolution of energy distributions of the primary and secondary
particles in the -ray production region.Comment: submitted to A&
Fermi Large Area Telescope observations of the supernova remnant HESS J1731-347
Context: HESS J1731-347 has been identified as one of the few TeV-bright
shell-type supernova remnants (SNRs). These remnants are dominated by
nonthermal emission, and the nature of TeV emission has been continuously
debated for nearly a decade.
Aims: We carry out the detailed modeling of the radio to gamma-ray spectrum
of HESS J1731-347 to constrain the magnetic field and energetic particles
sources, which we compare with those of the other TeV-bright shell-type SNRs
explored before.
Methods: Four years of data from Fermi Large Area Telescope (LAT)
observations for regions around this remnant are analyzed, leading to no
detection correlated with the source discovered in the TeV band. The Markov
Chain Monte Carlo method is used to constrain parameters of one-zone models for
the overall emission spectrum.
Results: Based on the 99.9% upper limits of fluxes in the GeV range, one-zone
hadronic models with an energetic proton spectral slope greater than 1.8 can be
ruled out, which favors a leptonic origin for the gamma-ray emission, making
this remnant a sibling of the brightest TeV SNR RX J1713.7-3946, the Vela
Junior SNR RX J0852.0-4622, and RCW 86. The best-fit leptonic model has an
electron spectral slope of 1.8 and a magnetic field of about 30 muG, which is
at least a factor of 2 higher than those of RX J1713.7-3946 and RX
J0852.0-4622, posing a challenge to the distance estimate and/or the energy
equipartition between energetic electrons and the magnetic field of this
source. A measurement of the shock speed will address this challenge and has
implications on the magnetic field evolution and electron acceleration driven
by shocks of SNRs.Comment: 7 pages, 3 fogures, A&A in pres
The diffuse gamma-ray emission toward the Galactic mini starburst W43
In this paper we report the Fermi Large Area Telescope (LAT) detection of the
gamma-ray emission toward the young star forming region W43. Using the latest
source catalog and diffuse background models, the extended gamma-ray excess is
detected with a significance of about 16 . The gamma-ray emission has a
spectrum with a photon index of . We also performed a detailed
analysis of the gas content in this region by taking into account the opacity
correction to the HI gas column density. The total cosmic-ray (CR) proton
energy is estimated to be on the order of assuming the
gamma-ray are produced from the interaction of the accelerated protons and
nuclei with the ambient gas. Comparing this region to the other star formation
regions in our Galaxy, we find that the CR luminosity is better correlated with
the wind power than the star formation rate (SFR). This result suggests that
CRs are primarily accelerated by stellar wind in these systemsComment: accepted for publications in A&
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