Shock acceleration of solar cosmic rays

We investigated the acceleration of solar cosmic rays (SCRs) by the shock waves produced by coronal mass ejections. We performed detailed numerical calculations of the SCR spectra produced during the shock propagation in the solar corona in terms of a model based on the diffusive transport equation using a realistic set of physical parameters for the corona. The resulting SCR energy spectrum N(ε) ∝ ε^?γ exp [? (ε/ε_max)^α] is shown to include a power-law portion with an index γ?2 that ends with an exponential tail with α ? 2.5 ? β, where β is the spectral index of the background Alfvén turbulence. The maximum SCR energy lies within the range ε_max = 1–300 MeV, depending on the shock velocity. Because of the steep spectrum of the SCRs, their backreaction on the shock structure is negligible. The decrease in the Alfvén Mach number of the shock due to the increase in the Alfvén velocity with heliocentric distance r causes the efficient SCR acceleration to terminate when the shock reaches a distance of r = 2–3R_⊙. Since the diffusive SCR propagation in this case is faster than the shock expansion, SCR particles intensively escape from the shock vicinity. A comparison of the calculated SCR fluxes expected near the Earth’s orbit with available experimental data indicates that the theory satisfactorily explains all of the main observed features.     

Ballistic and diffusive components in the dynamic spectra of ultrahigh energy cosmic rays from nearby transient sources

Ultrahigh energy cosmic rays (UHECRs, E > 10¹⁸ eV) from extragalactic sources deviate in the galactic and intergalactic magnetic fields, which explains the diffusive character of their propagation, the isotropization of their total flux, and the absence of UHECR clusters associated with individual sources. Extremely high energy cosmic rays (E > 10^19.7 eV) are scattered mainly in localized magnetized structures, such as galaxy clusters, filaments, etc., with a mean free path of tens of megaparsecs; therefore, in the case of nearby transient sources, a substantial contribution to the observed flux is expected from unscattered and weakly scattered particles, which may be a decisive factor in the identification of these sources. We propose a method for calculating the time evolution of the UHECR energy spectra based on analytical solutions of the transport equation with the explicit determination of the contributions from scattered and unscattered particles. As examples, we consider the cases of transient activity of the nearest active galactic nucleus, Centaurus A, and the acceleration of UHECRs by a young millisecond pulsar.     

Modeling the linear polarization of optical emission from red giants

We present the results of solving the radiative transfer equation for the Stokes vector in the case of light scattering by spherical forsterite dust particles in an axisymmetric circumstellar envelope of a red giant. We have assumed that the surfaces of constant scattering-particle density are prolate or oblate spheroids, the particle density decreases with radius as N _d ∝ r ⁻², and the dust particles at the inner boundary of the envelope are in thermal equilibrium with the stellar emission at solid-phase evaporation temperature T _ev = 800 K. In the wavelength range 0.27 μm ≤ λ ≤ 1 μm, particles with radii 0.03 μm ≲ a ≲ 0.2 μm make a major contribution to the linear polarization of the stellar emission. The increase in scattering efficiency factor with decreasing wavelength λ is mainly responsible for the growth of polarization toward the short wavelengths known from observations. However, at a mean number of scatterings 1.2 ≤ N _sca ≤ 1.6, the polarization ceases to grow due to depolarization effects and decreases rapidly as the wavelength decreases further. The wavelength of the polarization maximum is determined mainly by two quantities: the particle radius and the mass loss rate. The upper limits for the degree of linear polarization in the case of light scattering in circumstellar dust envelopes with the geometries of prolate and oblate spheroids are p ≈ 3 and 5%, respectively. The polarization for light scattering by enstatite particles is higher than that for light scattering by forsterite particles approximately by 0.3%. Original Russian Text ? Yu.A. Fadeyev, 2007, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2007, Vol. 33, No. 2, pp. 123–133.     

Cosmic ray scattering in compressible turbulence

We study the scattering of low-energy cosmic rays (CRs) in a turbulent, compressive magnetohydrodynamic (MHD) fluid. We show that compressible MHD modes – fast or slow waves with wavelengths smaller than CR mean free paths induce cyclotron instability in CRs. The instability feeds the new small-scale Alfvénic wave component with wavevectors mostly along magnetic field, which is not a part of the MHD turbulence cascade. This new component gives feedback on the instability through decreasing the CR mean free path. We show that the ambient turbulence fully suppresses the instability at large scales, while wave steepening constrains the amplitude of the waves at small scales. We provide the energy spectrum of the plane-parallel Alfvénic component and calculate mean free paths of CRs as a function of their energy. We find that for the typical parameters of turbulence in the interstellar medium and in the intercluster medium the new Alfvénic component provides the scattering of the low-energy CRs that exceeds the direct resonance scattering by MHD modes. This solves the problem of insufficient scattering of low-energy CRs in the turbulent interstellar or intracluster medium that was reported in the literature.     

WMAP-2006: Cosmological parameters and large-scale structure of the universe

The parameters of the cosmological model with cold dark matter and cosmological constant (ΛCDM model) were determined using three-year Wilkinson Microwave Anisotropy Probe observations of cosmic microwave background together with some data on the large-scale structure of the universe. The data cover scales from 1 to 10 000 Mpc. The best-fit ΛCDM model parameters were derived by minimizing the x ² statistic with the use of the Levenberg-Markquardt approach (Ω_Λ = 0.736 ± 0.065, Ω_m = 0.238 ± 0.080, Ω_b = 0.05 ± 0.011, h = 0.68 ± 0.09, σ₈ = 0.73 ± 0.08, and n _s = 0.96 ± 0.015). The ΛCDM model with these parameters is shown to agree well with the angular power spectrum of cosmic microwave background temperature fluctuations and with the density perturbation power spectra estimated from spatial distributions of galaxies and rich clusters of galaxies as well as from the statistics of the Ly _α absorption lines in the spectra of distant quasars. The accord between the model large-scale structure characteristics and the observed ones is analyzed, and conceivable factors causing appreciable discrepancies between some characteristics are discussed.     

Possible variability of the magnetic field of T Tau

Using the Main Stellar Spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a polametric analyzer, we measured the longitudinal magnetic field component B_∥ for the T Tauri stars T Tau and AS 507 on January 16 and 18 and February 15, 2003. For both stars, we determined only the upper limits on B_∥ from photospheric lines: +15±30 G for T Tau and ?70±90 G for AS 507. The magnetic field of AS 507 was not measured previously, while B_∥ for T Tau is lower than its values that we obtained in 1996 and 2002 (B_∥?150±50G), suggesting that the longitudinal magnetic field component in the photosphere of T Tau is variable. We also measured the longitudinal magnetic field component for T Tau in the formation region of the He I 5876 Å emission line. We found B_∥ in this region to be ?+650, ?+350, and ?+1100 G on January 16, 18, and February 15, 2003, respectively. Our observations on January 18 and February 15 correspond to virtually the same phase of the star's rotation period, but the profiles of the He I 5876 Å line differ markedly on these two nights. Therefore, we believe that the threefold difference between the B_∥ values on these nights does not result from observational errors. We discuss the possible causes of the B_∥ variability in the photosphere and the magnetosphere of T Tau.     

Primordial hydrogen recombination dynamics with recoil upon scattering in the Ly-<Emphasis Type="Italic">α</Emphasis> line

We show that including the recoil upon scattering in the Ly-α line can lead to a noticeable acceleration of the primordial hydrogen recombination. Thus, for example, for the ΛCDM model, the decrease in the degree of ionization exceeds 1% at redshifts z = 800–1050, reaching ≈1.3% at z = 900. The corresponding corrections to the calculated cosmic microwave background power spectra reach 1.1% and 1.7% for TT and EE spectra, respectively. The radiative transfer in these calculations was treated in the quasi-stationary approximation.We have also obtained numerical solutions (in the diffusion approximation) to the nonstationary problem of radiative transfer in the Ly-α line for a partial frequency redistribution with recoil. We trace the evolution of the local line profile and the relative number of uncompensated transitions from the 2p state to the 1s state. We show that including the nonstationarity of the Ly-α line radiative transfer can lead to an additional acceleration of the primordial hydrogen recombination.     

The sun,the cosmic vibration,and the nucleus of the galaxy 4151

Numerous U and V magnitude measurements were performed for the nucleus of the Seyfert galaxy NGC 4151 at the Crimean Laboratory of the SAI (Moscow University) in 1994–2005. Adding them to the previous data for 1968–1997 has led to a substantial increase in the confidence level of the light variations in NGC 4151 with a stable period of P _G = 160.0108(7) min and a mean amplitude of 0.007 U mag (in the “active” state of the nucleus). The period of NGC 4151 agrees well with the period of 160.0101(15) min found previously in the oscillations of the Sun. It is treated as the period of a “coherent cosmic oscillation” independent of redshift z or as the period of “free cosmic vibrations” of the hydrogen atom, the main element of the Universe. The period and initial phase of the P _G oscillation have been constant for 38 years of NGC 4151 observations. The new astrophysical phenomenon appears to be closely related to the quantum nonlocality of photons and is of particular interest in physics and cosmology.     

Energy changes of cosmic rays in the interplanetary region

A clarification and discussion of the energy changes experienced by cosmic rays in the interplanetary region is presented. It is shown that the mean time rate of change of momentum of cosmic rays reckoned for a fixed volume in a reference frame fixed in the solar system is 〈p〉 =p V·G/3 (p=momentum,V is the solar wind velocity andG=cosmic-ray density gradient). This result is obtained in three ways:

1. by a rearrangement and reinterpretation of the cosmic-ray continuity equation;
2. by using a scattering analysis based on that of Gleeson and Axford (1967);
3. by using a special scattering model in which cosmic-rays are trapped in ‘magnetic boxes’ moving with the solar wind.

The third method also gives the rate of change of momentum of particles within a moving ‘magnetic box’ as 〈p〉_ad = ?p ?·V/3, which is the adiabatic deceleration rate of Parker (1965). We conclude that ‘turnaround’ energy change effects previously considered separately are already included in the equation of transport for cosmic rays.     

Hydrodynamic processes of angular momentum transport in the interior of a rotating massive hydrogen-burning star

The evolution of a rotating star with a mass of 16M _⊙ at the hydrogen burning phase is considered together with the hydrodynamic processes of angular momentum transport in its interior. Shear turbulence is shown to limit the amplitude of the latitudinal variations in mean molecular weight on a surface of constant pressure in a layer with variable chemical composition. The resulting nonuniformity in the mean molecular weight distribution and the turbulent energy transport along the surface of constant pressure reduce the absolute value of the meridional circulation velocity. Nevertheless, meridional circulation remains the main mechanism of angular momentum transport in the radial direction in a layer with variable chemical composition. The intensity of the processes of angular momentum transport by meridional circulation and shear turbulence is determined by the angular momentum of the star. At a fairly high angular momentum, more specifically, at J = 3.69 × 10⁵² g cm² s^?1, the star during the second half of the hydrogen-burning phase in its convective core has characteristics typical of classical early Be stars.     

The possibility of investigating ultra-high-energy cosmic-ray sources using data on the extragalactic diffuse gamma-ray emission

We provide our estimates of the intensity of the gamma-ray emission with an energy near 0.1 TeV generated in intergalactic space in the interactions of cosmic rays with background emissions. We assume that the cosmic-ray sources are pointlike and that these are active galactic nuclei. The following possible types of sources are considered: remote and powerful ones, at redshifts up to z = 1.1, with a monoenergetic particle spectrum, E = 10²¹ eV; the same objects, but with a power-law particle spectrum; and nearby sources at redshifts 0 < z ≤ 0.0092, i.e., at distances no larger than 50 Mpc also with a power-law particle spectrum. The contribution of cosmic rays to the extragalactic diffuse gammaray background at an energy of 0.1 TeVhas been found to depend on the type of sources or, more specifically, the contribution ranges from f ? 10^?4 to f ≈ 0.1, depending on the source model. We conclude that the data on the extragalactic background gamma-ray emission can be used to determine the characteristics of extragalactic cosmic-ray sources, i.e., their distances and the pattern of the particle energy spectrum.     

The fundamental plane and other scaling relations for galaxy groups and clusters

In this paper we study the relations between the main characteristics of groups and clusters of galaxies using the archival data of the SDSS and 2MASX catalogs. We have developed and implemented a new method of determining the size of galaxy systems and their effective radius which contains half of the galaxies and not half the luminosity, since the luminosity of the brightest galaxy in a group can account for over 50% of the total luminosity of the group. The derived parameters (log L_K, logR_e, and log σ₂₀₀) for 94 systems of galaxies (0.0038 < z < 0.09) determine the Fundamental Plane (FP), which, with a scatter of 0.15, is similar in form to the FP of galaxy clusters obtained by Schaeffer et al. (1993) and D’Onofrio et al. (2013) with other methods and for different bands. We show that the FP in the near-infrared region (NIR) for 94 galaxy systems has the form of L_K ∝ \(R_e^{0.70 \pm {{0.13}_\sigma }1.34 \pm 0.13}\), whereas in x-rays it has the form of—L_X ∝ \(R_e^{1.15 \pm {{0.39}_\sigma }2.56 \pm 0.40}\). The form of the FP for groups and clusters is consistent with the FP for early-type galaxies determined in the same way. The form of the FP for galaxy systems deviates from the shape that one would expect from virial predictions. Adding the mass-to-light ratio as a fourth independent parameter has little effect on this deviation, but decreases the scatter of the FP for a sample of rich galaxy clusters by 12%.     

A model of possible variations of the galactic cosmic ray intensity over the recent billion years

Based on the analysis of published data on exposure ages of iron meteorites determined with the ⁴⁰K/K method (T _K) and ages calculated using short-lived cosmogenic radionuclides (with the half-life T _1/2 < 1 Myr) in combination with stable cosmogenic isotopes of noble gases (T_RS), the following results have been obtained. (1) The distribution of T _RS ages (106 values) has an exponential shape, similar to that for ordinary chondrites, but different from the distribution of T _K ages (80 values). The difference is most likely due to small amounts of data for meteorites with low T _K ages (less than ~200–300 Myr). The latter can be ascribed to the difficulty of measurement of small concentrations of cosmogenic potassium isotopes. This circumstance makes the selection of meteorites with ⁴⁰K/K ages nonrepresentative and casts doubt on the correctness of conclusions about the variations of the intensity of galactic cosmic rays (GCR) based on the analysis of distribution of these ages. (2) The magnitude of the known effect (systematic overestimation of T _K ages in comparison with T _RS ages) has been refined. The value k = T _K/T _RS = 1.51 ± 0.03 is acquired for the whole population of data. We have shown the inefficiency of the explanation of this effect on account of an exponential change in the GCR intensity (I _T ) with time (T) according to the relation I _T = I ₀exp(–γT) over the whole range of ages of iron meteorites. (3) In order to explain the overestimation of T _K ages in comparison with T _RS ages, a model has been proposed, according to which the GCR intensity has exponentially increased in the interval of 0–1500 Myr governed by the relation: I _T = I _{T = 1500} (1 + αexp(–βT)). For one of the variants of this model, the GCR intensity has exponentially increased by a factor of two only over the recent ~300 Myr, remaining approximately constant for the rest of the time. The data acquired with the use of this model indicate that the measured T _K ages are close to the actual time that the meteorites existed in space; the data are in agreement with the observed exponential distribution of T _RS ages.     

Infrared luminosities of local-volume galaxies

Based on data from the Two-Micrometer All-Sky Survey (2MASS), we analyzed the infrared properties of 451 Local-Volume galaxies at distances D ≤ 10 Mpc. We determined the K-band luminosity function of the galaxies in the range of absolute magnitudes from ?25^m to ?11^m. The local luminosity density within 8 Mpc is 6.8 × 10⁸L_⊙ Mpc^?3, a factor of 1.5 ± 0.1 higher than the global mean K-band luminosity density. We determined the ratios of the virial mass to the K-band luminosity for nearby groups and clusters of galaxies. In the luminosity range from 5 × 10¹⁰ to 2 × 10¹³L_⊙, the dependence log(M/L_K) ∝ (0.27 ± 0.03) log L_K with a dispersion of ～0.1 comparable to the measurement errors of the masses and luminosities of the systems of galaxies holds for the groups and clusters of galaxies. The ensemble-averaged ratio, 〈M/L_K〉 ? (20–25) M_⊙/L_⊙, was found to be much smaller than the expected global ratio, (80–90)M_⊙/L_⊙, in the standard model with Ω_m = 0.27. This discrepancy can be eliminated if the bulk of the dark matter in the Universe is not associated with galaxies and their systems.     

KDG218, a nearby ultra-diffuse galaxy

We present properties of the low-surface-brightness galaxy KDG218 observed with the HST/ACS. The galaxy has a half-light (effective) diameter of a _e = 47″ and a central surface brightness of SB _V (0) = 24.^m4/□″. The galaxy remains unresolved with the HST/ACS, which implies its distance of D > 13.1 Mpc and linear effective diameter of A _e > 3.0 kpc. We notice that KDG218 is most likely associated with a galaxy group around the massive lenticular NGC4958 galaxy at approximately 22 Mpc, or with the Virgo Southern Extension filament at approximately 16.5 Mpc. At these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG) similar to those found in the Virgo, Fornax, and Coma clusters. We also present a sample of 15 UDG candidates in the Local Volume. These sample galaxies have the following mean parameters: 〈D〉 = 5.1 Mpc, 〈A _e 〉 = 4.8 kpc, and 〈SB _B (e)〉 = 27.^m4/□″. All the local UDG candidates reside near massive galaxies located in the regions with the mean stellar mass density (within 1 Mpc) about 50 times greater than the average cosmic density. The local fraction of UDGs does not exceed 1.5% of the Local Volume population. We notice that the presented sample of local UDGs is a heterogeneous one containing irregular, transition, and tidal types, as well as objects consisting of an old stellar population.     

Analytic forms of the perpendicular cosmic ray diffusion coefficient for an arbitrary turbulence spectrum and applications on transport of Galactic protons and acceleration at interplanetary shocks

We investigate cosmic ray scattering in the direction perpendicular to a mean magnetic field. Unlike in previous articles we employ a general form of the turbulence wave spectrum with arbitrary behavior in the energy range. By employing an improved version of the nonlinear guiding center theory we compute analytically the perpendicular mean free path. As shown, the energy range spectral index, has a strong influence on the perpendicular diffusion coefficient. If this parameter is larger than one we find for some cases a perpendicular diffusion coefficient that is independent of the parallel mean free path and particle energy. Two applications are considered, namely transport of Galactic protons in the solar system and diffusive particle acceleration at highly perpendicular interplanetary shock waves.     

A catalog of cosmic gamma-ray bursts detected by the PHEBUS instrument on the Granat observatory: October 1994–December 1996

We present the final part of the catalog of cosmic gamma-ray bursts (GRBs) observed in the PHEBUS experiment on the Granat orbiting astrophysical observatory. The first three parts of the catalog were published by Terekhov et al. (1994, 1995a) and Tkachenko et al. (1998). The fourth part contains information on 32 events recorded from October 1994 until December 1996. We give burst light curves in the energy range 100 keV to 1.6 MeV, integrated energy spectra, and information on the fluence and energy flux at the luminosity peak for energies above 100 keV. Over the entire period of its operation, the PHEBUS instrument detected 206 cosmic GRBs. The mean ?V/V_max? was 0.336±0.007. The mean hardness corresponding to the ratio of count numbers in the energy ranges 400–1000 and 100–400 keV is 0.428±0.018 for events with a duration shorter than 2 s and 0.231±0.004 for events with a duration longer than 2 s.     

Role of anisotropy of the initial particle distribution in the acceleration in collapsing solar-flare traps

We consider the behavior of charged particles with an anisotropic initial velocity distribution in a magnetic trap with approaching mirrors in connection with the problem of particle acceleration in solar flares. We show that, irrespective of the charge sign, the efficiency of confinement and acceleration increases with increasing anisotropy factor of the initial distribution α = (T_⊥/T_∥)^1/2. For a positive electric potential of the trap plasma relative to the mirrors, the emerging additional effect of ion expulsion form the trap increases with α_i. The derived estimate of the electric potential suggests an amplification of the initial perturbation and the development of instability.     

Studying the influence of turbulent mixing on thermonuclear burning regimes during X-ray bursts of neutron stars using the <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">ε</Emphasis></Subscript> model

We study the influence of turbulent mixing on the development of thermonuclear flashes in the surface layers of neutron stars. A simple K _ε model that includes various physical processes is used to describe the turbulent processes. In contrast to the widespread mixing-length theory, the K _ε model does not require using additional dimensional parameters, traces the development of turbulence in dynamics, describes the various turbulence development scenarios (gravitational and shear instabilities, convection, semiconvection, etc.) in a unified way, and can be used in multidimensional numerical simulations. Empirical constants of the model are chosen on the basis of experimental data and direct numerical simulations of typical processes. We have used the Era and Tigr-3T software packages to numerically simulate thermonuclear flashes in the accretion-renewable atmospheres of neutron stars. Turbulence is shown to accelerate significantly the transport of released energy to the stellar surface. Mixing equalizes the concentrations of matter components throughout the burning layer and increases the amount of matter involved in the thermonuclear burning during a flash.     

FRB Event Rate Predictions for the Ooty Wide Field Array

We developed a generic formalism to estimate the event rate and the redshift distribution of Fast Radio Bursts (FRBs) in our previous publication (Bera et al. 2016), considering FRBs are of an extragalactic origin. In this paper, we present (a) the predicted pulse widths of FRBs by considering two different scattering models, (b) the minimum total energy required to detect events, (c) the redshift distribution and (d) the detection rates of FRBs for the Ooty Wide Field Array (OWFA). The energy spectrum of FRBs is modelled as a power law with an exponent ?α and our analysis spans a range ?3≤α≤5. We find that OWFA will be capable of detecting FRBs with α≥0. The redshift distribution and the event rates of FRBs are estimated by assuming two different energy distribution functions; a Delta function and a Schechter luminosity function with an exponent ?2≤γ≤2. We consider an empirical scattering model based on pulsar observations (model I) as well as a theoretical model (model II) expected for the intergalactic medium. The redshift distributions peak at a particular redshift z _p for a fixed value of α, which lie in the range 0.3≤z _p ≤1 for the scattering model I and remain flat and extend up to high redshifts (z?5) for the scattering model II.