TY - JOUR A1 - Vafin, Sergei A1 - Deka, Pranab Jyoti A1 - Pohl, Martin A1 - Bohdan, Artem T1 - Revisit of Nonlinear Landau Damping for Electrostatic Instability Driven by Blazar-induced Pair Beams JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We revisit the effect of nonlinear Landau (NL) damping on the electrostatic instability of blazar-induced pair beams, using a realistic pair-beam distribution. We employ a simplified 2D model in k-space to study the evolution of the electric-field spectrum and to calculate the relaxation time of the beam. We demonstrate that the 2D model is an adequate representation of the 3D physics. We find that nonlinear Landau damping, once it operates efficiently, transports essentially the entire wave energy to small wave numbers where wave driving is weak or absent. The relaxation time also strongly depends on the intergalactic medium temperature, T-IGM, and for T-IGM << 10 eV, and in the absence of any other damping mechanism, the relaxation time of the pair beam is longer than the inverse Compton (IC) scattering time. The weak late-time beam energy losses arise from the accumulation of wave energy at small k, that nonlinearly drains the wave energy at the resonant k of the pair-beam instability. Any other dissipation process operating at small k would reduce that wave-energy drain and hence lead to stronger pair-beam energy losses. As an example, collisions reduce the relaxation time by an order of magnitude, although their rate is very small. Other nonlinear processes, such as the modulation instability, could provide additional damping of the nonresonant waves and dramatically reduce the relaxation time of the pair beam. An accurate description of the spectral evolution of the electrostatic waves is crucial for calculating the relaxation time of the pair beam. KW - gamma rays: general KW - instabilities KW - magnetic fields KW - relativistic processes KW - waves Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab017b SN - 0004-637X SN - 1538-4357 VL - 873 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Vafin, Sergei A1 - Riazantseva, Maria A1 - Pohl, Martin T1 - Coulomb collisions as a candidate for temperature anisotropy constraints in the solar wind JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Many solar wind observations at 1 au indicate that the proton (as well as electron) temperature anisotropy is limited. The data distribution in the (A(a), beta(a),(parallel to))-plane have a rhombic-shaped form around beta(a),(parallel to) similar to 1. The boundaries of the temperature anisotropy at beta(a),(parallel to) > 1 can be well explained by the threshold conditions of the mirror (whistler) and oblique proton (electron) firehose instabilities in a bi-Maxwellian plasma, whereas the physical mechanism of the similar restriction at beta(a),(parallel to) < 1 is still under debate. One possible option is Coulomb collisions, which we revisit in the current work. We derive the relaxation rate nu(A)(aa) of the temperature anisotropy in a bi-Maxwellian plasma that we then study analytically and by observed proton data from WIND. We found that nu(A)(pp) increases toward small beta(p),(parallel to) < 1. We matched the data distribution in the (A(p), beta(p),(parallel to))-plane with the constant contour nu(A)(pp) = 2.8 . 10(-6) s(-1), corresponding to the minimum value for collisions to play a role. This contour fits rather well the left boundary of the rhombic-shaped data distribution in the (A(p), beta(p),(parallel to))-plane. Thus, Coulomb collisions are an interesting candidate for explaining the limitations of the temperature anisotropy in the solar wind with small beta(a),(parallel to) < 1 at 1 au. KW - instabilities KW - plasmas KW - scattering KW - solar wind KW - Sun: heliosphere Y1 - 2019 U6 - https://doi.org/10.3847/2041-8213/aafb11 SN - 2041-8205 SN - 2041-8213 VL - 871 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Bohdan, Artem A1 - Niemiec, Jacek A1 - Pohl, Martin A1 - Matsumoto, Yosuke A1 - Amano, Takanobu A1 - Hoshino, Masahiro T1 - Kinetic Simulations of Nonrelativistic Perpendicular Shocks of Young Supernova Remnants BT - I. Electron Shock-surfing Acceleration JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Electron injection at high Mach number nonrelativistic perpendicular shocks is studied here for parameters that are applicable to young SNR shocks. Using high-resolution large-scale two-dimensional fully kinetic particle-in-cell simulations and tracing individual particles, we in detail analyze the shock-surfing acceleration (SSA) of electrons at the leading edge of the shock foot. The central question is to what degree the process can be captured in 2D3V simulations. We find that the energy gain in SSA always arises from the electrostatic field of a Buneman wave. Electron energization is more efficient in the out-of-plane orientation of the large-scale magnetic field because both the phase speed and the amplitude of the waves are higher than for the in-plane scenario. Also, a larger number of electrons is trapped by the waves compared to the in-plane configuration. We conclude that significant modifications of the simulation parameters are needed to reach the same level of SSA efficiency as in simulations with out-of-plane magnetic field or 3D simulations. KW - acceleration of particles KW - instabilities KW - ISM: supernova remnants KW - methods: numerical KW - plasmas KW - shock waves Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab1b6d SN - 0004-637X SN - 1538-4357 VL - 878 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER -