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 $\sim 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. 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 $10^{14}$ 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 $B_\mathrm{d}\approx 20$ 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 $\epsilon_{\gamma}F_{\gamma}\approx 4\times 10^{-13}$ erg cm$^2$s$^{-1}$ 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 $10^{17}$ 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

A Direct Comparison of Muon Measurements at the Yakutsk Array and the Pierre Auger Observatory

Here we consider the results of direct measurements of muons in extensive air showers with zenith angles $\theta \le 45^{\circ}$ and energy above $10^{17}$ eV, obtained at the Pierre Auger Observatory and Yakutsk array. In both experiments muons were registered with underground scintillation detectors with $\approx 1.0 \times \sec\theta$ GeV energy threshold. Measured density values were compared to theoretical predictions calculated within the framework of the QGSJet-II.04 hadron interaction model. They differ by factor $1.53 \pm 0.13$(stat). We demonstrate that this difference is due to overestimation of muon densities by 1.22 times and underestimation of primary energy by 1.25 times in the Auger experiment.Comment: 9 pages, 11 figures, 3 tables. Presented at the 4th International Symposium on Cosmic Rays and Astrophysics (https://indico.nevod.mephi.ru/event/9/contributions/226/). To be published in Physics of Atomic Nucle