249 research outputs found
Re-examination of the Expected gamma-ray emission of supernova remnant SN 1987A
A nonlinear kinetic theory, combining cosmic-ray (CR) acceleration in
supernova remnants (SNRs) with their gas dynamics, is used to re-examine the
nonthermal properties of the remnant of SN 1987A for an extended evolutionary
period of 5-50 yr. This spherically symmetric model is approximately applied to
the different features of the SNR which consist of (i) a blue supergiant wind
and bubble, and (ii) of the swept-up red supergiant (RSG) wind structures in
the form of an H II region, an equatorial ring (ER), and an hourglass region.
The RSG wind involves a mass loss rate that decreases significantly with
elevation above and below the equatorial plane. The model adapts recent
three-dimensional hydrodynamical simulations by Potter et al. in 2014 that use
a significantly smaller ionized mass of the ER than assumed in the earlier
studies by the present authors. The SNR shock recently swept up the ER, which
is the densest region in the immediate circumstellar environment. Therefore,
the expected gamma-ray energy flux density at TeV energies in the current epoch
has already reached its maximal value of erg cm
s. This flux should decrease by a factor of about two over the next 10
years.Comment: 5 pages, 7 figures, accepted for publication in ApJ, Appendix adde
The nature of gamma-ray emission of Tycho's supernova remnant
The nature of the recently detected HE and VHE gamma-ray emission of Tycho's
supernova remnant (SNR) is studied. A nonlinear kinetic theory of cosmic ray
(CR) acceleration in supernova remnants (SNRs) is employed to investigate the
properties of Tycho's SNR and their correspondence to the existing experimental
data, taking into account that the ambient interstellar medium (ISM) is
expected to be clumpy. It is demonstrated that the overall steep gamma-ray
spectrum observed can be interpreted as the superposition of two spectra
produced by the CR proton component in two different ISM phases: The first
gamma-ray component, extending up to about eV, originates in the
diluted warm ISM, whereas the second component, extending up to 100 GeV, comes
from numerous dense, small-scale clouds embedded in this warm ISM. Given the
consistency between acceleration theory and the observed properties of the
nonthermal emission of Tycho's SNR, a very efficient production of nuclear CRs
in Tycho's SNR is established. The excess of the GeV gamma-ray emission due to
the clouds' contribution above the level expected in the case of a purely
homogeneous ISM, is inevitably expected in the case of type Ia SNe.Comment: 6 pages, 1 figure, accepted by Ap
Expected gamma-ray emission of supernova remnant SN 1987A
A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to re-examine the nonthermal properties of the remnant of
SN 1987A for an extended evolutionary period of 5--100 yr. It is shown that an
efficient production of nuclear CRs leads to a strong modification of the outer
supernova remnant shock and to a large downstream magnetic field
mG. The shock modification and the strong field are
required to yield the steep radio emission spectrum observed, as well as to
considerable synchrotron cooling of high energy electrons which diminishes
their X-ray synchrotron flux. These features are also consistent with the
existing X-ray observations. The expected \gr energy flux at TeV-energies at
the current epoch is nearly erg cms under reasonable assumptions about the overall
magnetic field topology and the turbulent perturbations of this field. The
general nonthermal strength of the source is expected to increase roughly by a
factor of two over the next 15 to 20 yrs; thereafter it should decrease with
time in a secular form.Comment: 7 pages, 5 figures, accepted for publication in ApJ, a number of
changes have been made, even though these are not changing the main results
of the pape
Internal dynamics and particle acceleration in Tycho's SNR
The consequences of a newly suggested value for the SN explosion energy
1.2x10^{51} erg are explored for the case of Tycho's supernova remnant (SNR). A
nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs is employed to
investigate the properties of Tycho's SNR and their correspondence to the
existing experimental data. It is demonstrated that the large mean ratio
between the radii of the contact discontinuity and the forward shock is
consistent with the very effective acceleration of nuclear energetic particles
at the forward shock. It is also argued that consistency of the value E_{sn} =
1.2x10^{51} erg with the gas dynamics, acceleration theory, and the existing
gamma-ray measurements requires the source distance to be greater than 3.3 kpc.
The corresponding ambient gas number density is lower than 0.4 cm^{-3}. Since
the expected gamma-ray flux strongly depends on the source distance,
F_{\gamma}\propto d^{-7}, a future experimental determination of the actual
gamma-ray flux from Tycho's SNR will make it possible to determine the values
of the source distance and of the mean ambient gas density. A simple inverse
Compton model without a dominant population of nuclear CRs is not compatible
with the present upper limit for the gamma-ray emission for any reasonable
ambient interstellar B-field. Given the consistency between acceleration theory
and overall, as well as internal, gas dynamics, a future gamma-ray detection
would make the case for nuclear particle acceleration in Tycho's SNR
incontrovertible in our view.Comment: 8 pages, 4 figures, Accepted for publication in A&
Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure
The temperature and pressure dependence of the partial density of phonon
states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear
inelastic scattering (NIS). The high energy resolution allows for a detailed
observation of spectral properties. A sharpening of the optical phonon modes
and shift of all spectral features towards higher energies by ~4% with
decreasing temperature from 296 K to 10 K was found. However, no detectable
change at the tetragonal - orthorhombic phase transition around 100 K was
observed. Application of a pressure of 6.7 GPa, connected with an increase of
the superconducting temperature from 8 K to 34 K, results in an increase of the
optical phonon mode energies at 296 K by ~12%, and an even more pronounced
increase for the lowest-lying transversal acoustic mode. Despite these strong
pressure-induced modifications of the phonon-DOS we conclude that the
pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the
framework of classical electron-phonon coupling. This result suggests the
importance of spin fluctuations to the observed superconductivity
Muon puzzle in ultra-high energy EASs according to Yakutsk array and Auger experiment data
The lateral distribution of particles in extensive air showers from cosmic
rays with energy above eV registered at the Yakutsk complex array was
analyzed. Experimentally measured particle densities were compared to the
predictions obtained within frameworks of three ultra-high energy hadron
interaction models. The cosmic ray mass composition estimated by the readings
of surface-based and underground detectors of the array is consistent with
results based on the Cherenkov light lateral distribution data. A comparison
was made with the results of direct measurement of the muon component performed
at the Pierre Auger Observatory. It is demonstrated that the densities of muon
flux measured at Yakutsk array are consistent with results of fluorescent light
measurements and disagree with results on muons obtained at the Auger array.Comment: 14 pages, 6 figures, 2 tables. Accepted for publication in JETP
Letter
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