339 research outputs found
Cosmic Ray acceleration and Balmer emission from SNR 0509-67.5
Context: Observation of Balmer lines from the region around the forward shock
of supernova remnants may provide precious information on the shock dynamics
and on the efficiency of particle acceleration at the shock.
Aims: We calculate the Balmer line emission and the shape of the broad Balmer
line for parameter values suitable for SNR 0509-67.5, as a function of the
cosmic ray acceleration efficiency and of the level of thermal equilibration
between electrons and protons behind the shock. This calculation aims at using
the width of the broad Balmer line emission to infer the cosmic ray
acceleration efficiency in this remnant.
Methods: We use the recently developed non-linear theory of diffusive shock
acceleration in the presence of neutrals. The semi-analytical approach that we
developed includes a description of magnetic field amplification as due to
resonant streaming instability, the dynamical reaction of both accelerated
particles and turbulent magnetic field on the shock, and all channels of
interaction between neutral atoms and background plasma that change the shock
dynamics.
Results: We achieve a quantitative assessment of the CR acceleration
efficiency in SNR 0509-67.5 as a function of the shock velocity and different
levels of electron-proton thermalization in the shock region. If the shock
moves faster than ~4500 km/s, one can conclude that particle acceleration must
be taking place with efficiency of several tens of percent. For lower shock
velocity the evidence for particle acceleration becomes less clear because of
the uncertainty in the electron-ion equilibration downstream. We also discuss
the role of future measurements of the narrow Balmer line.Comment: 7 pages, 5 figure. Accepted for publication in Astronomy &
Astrophysic
Contribution to diffuse gamma-ray emission coming from self-confined CRs around their Galactic sources
Recent observations of the diffuse Galactic gamma-ray emission by the
Fermi-LAT satellite have shown significant deviations from models which assume
the same diffusion properties for cosmic rays (CR) throughout the Galaxy. We
explore the possibility that a fraction of this diffuse Galactic emission could
be due to hadronic interactions of CRs self-confined in the region around their
sources. In fact, freshly accelerated CRs that diffuse away from the
acceleration region can trigger the streaming instability able to amplify
magnetic disturbance and to reduce the particle diffusion. When this happen,
CRs are trapped in the near source region for a time longer than expected and
an extended gamma-ray halo is produces around each source. Here we calculate
the contribution to the diffuse gamma-ray background due to the overlap along
lines of sight of several of these extended halos. We find that if the density
of neutrals is low, the halos can account for a substantial fraction of the
diffuse emission observed by Fermi-LAT, depending on the orientation of the
line of sight with respect to the direction of the galactic center.Comment: 8 pages, 2 figs. Proceeding the 35th International Cosmic Ray
Conference (ICRC2017), Bexco, Busan, Kore
Broad Balmer line emission and cosmic ray acceleration efficiency in supernova remnant shocks
Balmer emission may be a powerful diagnostic tool to test the paradigm of
cosmic ray (CR) acceleration in young supernova remnant (SNR) shocks. The width
of the broad Balmer line is a direct indicator of the downstream plasma
temperature. In case of efficient particle acceleration an appreciable fraction
of the total kinetic energy of the plasma is channeled into CRs, therefore the
downstream temperature decreases and so does the broad Balmer line width. This
width also depends on the level of thermal equilibration between ions and
neutral hydrogen atoms in the downstream. Since in general in young SNR shocks
only a few charge exchange (CE) reactions occur before ionization,
equilibration between ions and neutrals is not reached, and a kinetic
description of the neutrals is required in order to properly compute Balmer
emission.
We provide a method for the calculation of Balmer emission using a
self-consistent description of the shock structure in the presence of neutrals
and CRs. We use a recently developed semi-analytical approach, where neutral
particles, ionized plasma, accelerated particles and magnetic fields are all
coupled together through the mass, momentum and energy flux conservation
equations. The distribution of neutrals is obtained from the full Boltzmann
equation in velocity space, coupled to Maxwellian ions through ionization and
CE processes. The computation is also improved with respect to previous work
thanks to a better approximation for the atomic interaction rates. We find that
for shock speeds >2500km/s the distribution of broad neutrals never approaches
a Maxwellian and its moments differ from those of the ionized component. These
differences reflect into a smaller FWHM than predicted in previous
calculations, where thermalization was assumed. The method presented here
provides a realistic estimate of particle acceleration efficiency in Balmer
dominated shocks.Comment: 6 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
Cosmic Ray acceleration and Balmer emission from RCW 86 (G315.4-2.3)
Context. Observation of Balmer lines from the region around the forward shock
of supernova remnants (SNR) may provide valuable information on the shock
dynamics and the efficiency of particle acceleration at the shock.
Aims. We calculated the Balmer line emission and the shape of the broad
Balmer line for parameter values suitable for SNR RCW 86 (G315.4-2.3) as a
function of the cosmic-ray (CR) acceleration efficiency and of the level of
thermal equilibration between electrons and protons behind the shock. This
calculation aims at using the width of the broad Balmer-line emission to infer
the CR acceleration efficiency in this remnant.
Methods. We used the recently developed nonlinear theory of diffusive
shock-acceleration in the presence of neutrals. The semianalytical approach we
developed includes a description of magnetic field amplification as due to
resonant streaming instability, the dynamical reaction of accelerated particles
and the turbulent magnetic field on the shock, and all channels of interaction
between neutral hydrogen atoms and background ions that are relevant for the
shock dynamics.
Results. We derive the CR acceleration efficiency in the SNR RCW 86 from the
Balmer emission. Since our calculation used recent measurements of the shock
proper motion, the results depend on the assumed distance to Earth. For a
distance of 2 kpc the measured width of the broad Balmer line is compatible
with the absence of CR acceleration. For a distance of 2.5 kpc, which is a
widely used value in current literature, a CR acceleration efficiency of 5-30%
is obtained, depending upon the electron-ion equilibration and the ionization
fraction upstream of the shock. By combining information on Balmer emission
with the measured value of the downstream electron temperature, we constrain
the CR acceleration efficiency to be ~20%.Comment: 7 pages, 6 figures. Accepted for publication in A&A (minor changes to
match the published version
Contribution to Galactic cosmic rays from young stellar clusters
The origin of Galactic cosmic rays (CR) is still a matter of debate.
Diffusive shock acceleration (DSA) applied to supernova remnant (SNR) shocks
provides the most reliable explanation. However, within the current
understanding of DSA several issues remain unsolved, like the CR maximum
energy, the chemical composition and the transition region between Galactic and
extra-Galactic CRs. These issues motivate the search for other possible
Galactic sources. Recently, several young stellar clusters (YSC) have been
detected in gamma rays, suggesting that such objects could be powerful sources
of Galactic CRs. The energy input could come from winds of massive stars hosted
in the clusters which is a function of the cluster total mass and initial mass
function of stars. In this work we evaluate the total CR flux produced by a
synthetic population of YSCs assuming that the CR acceleration occurs at the
termination shock of the collective wind resulting from the sum of cluster's
stellar winds. We show that the spectrum produced by YSC can significantly
contribute to energies TeV if the diffusion inside the wind-blown
bubble is Bohm-like and the spectral slope is harder than the one produced by
SNRs.Comment: Proceeding to the International Cosmic Ray Conference, ICRC 2023,
Nagoya, Japa
A 22-Week-Old Fetus with Nager Syndrome and Congenital Diaphragmatic Hernia due to a Novel SF3B4 Mutation.
Nager syndrome, or acrofacial dysostosis type 1 (AFD1), is a rare multiple malformation syndrome characterized by hypoplasia of first and second branchial arches derivatives and appendicular anomalies with variable involvement of the radial/axial ray. In 2012, AFD1 has been associated with dominant mutations in SF3B4. We report a 22-week-old fetus with AFD1 associated with diaphragmatic hernia due to a previously unreported SF3B4 mutation (c.35-2A>G). Defective diaphragmatic development is a rare manifestation in AFD1 as it is described in only 2 previous cases, with molecular confirmation in 1 of them. Our molecular finding adds a novel pathogenic splicing variant to the SF3B4 mutational spectrum and contributes to defining its prenatal/fetal phenotype
Gamma Rays and Neutrinos from SNR RX J1713.7-3946
The supernova paradigm for the origin of galactic cosmic rays can be tested
using multifrequency observations of both non-thermal and thermal emission from
supernova remnants. The smoking gun of hadronic acceleration in these sources
can, however, only be provided by the detection of a high energy neutrino
signal. Here we apply the theory of non-linear particle acceleration at
supernova shocks to the case of the supernova remnant RX J1713.7-3946, which is
becoming the stereotypical example of a possible hadronic accelerator after the
detection of high energy gamma rays by the HESS telescope. Our aim is twofold:
on one hand we want to address the uncertainties in the discrimination between
a hadronic and a leptonic interpretation of the gamma ray emission, mainly
related to the possibility of a statistical uncertainty in the energy
determination of the gamma ray photons in the TeV region. On the other we want
to stress how a km cube neutrino telescope would break the degeneracy and
provide evidence for efficient cosmic ray acceleration in RX J1713.7-3946. A 3
sigma evidence would require about two years of observation.Comment: 11 pages, 3 figures, accepted for publication in Astropaticle Physic
Collisionless shocks in a partially ionized medium: I. Neutral return flux and its effects on acceleration of test particles
A collisionless shock may be strongly modified by the presence of neutral
atoms through the processes of charge exchange between ions and neutrals and
ionization of the latter. These two processes lead to exchange of energy and
momentum between charged and neutral particles both upstream and downstream of
the shock. In particular, neutrals that suffer a charge exchange downstream
with shock-heated ions generate high velocity neutrals that have a finite
probability of returning upstream. These neutrals might then deposit heat in
the upstream plasma through ionization and charge exchange, thereby reducing
the fluid Mach number. A consequence of this phenomenon, that we refer to as
the "neutral return flux", is a reduction of the shock compression factor and
the formation of a shock precursor upstream. The scale length of the precursor
is determined by the ionization and charge exchange interaction lengths of fast
neutrals moving towards upstream infinity. In the case of a shock propagating
in the interstellar medium, the effects of ion-neutral interactions are
especially important for shock velocities < 3000 km/s. Such propagation
velocities are common among shocks associated with supernova remnants, the
primary candidate sources for the acceleration of Galactic cosmic rays. We then
investigate the effects of the return flux of neutrals on the spectrum of
test-particles accelerated at the shock. We find that, for shocks slower than
~3000 km/s, the particle energy spectrum steepens appreciably with respect to
the naive expectation for a strong shock, namely E^-2.Comment: 13 pages, 8 figures. Paper accepted for publication in the
Astrophysical Journa
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