TY - JOUR A1 - Vafin, Sergei A1 - Rafighi, Iman A1 - Pohl, Martin A1 - Niemiec, Jacek T1 - The Electrostatic Instability for Realistic Pair Distributions in Blazar/EBL Cascades JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - This work revisits the electrostatic instability for blazar-induced pair beams propagating through the intergalactic medium (IGM) using linear analysis and PIC simulations. We study the impact of the realistic distribution function of pairs resulting from the interaction of high-energy gamma-rays with the extragalactic background light. We present analytical and numerical calculations of the linear growth rate of the instability for the arbitrary orientation of wave vectors. Our results explicitly demonstrate that the finite angular spread of the beam dramatically affects the growth rate of the waves, leading to the fastest growth for wave vectors quasi-parallel to the beam direction and a growth rate at oblique directions that is only a factor of 2-4 smaller compared to the maximum. To study the nonlinear beam relaxation, we performed PIC simulations that take into account a realistic wide-energy distribution of beam particles. The parameters of the simulated beam-plasma system provide an adequate physical picture that can be extrapolated to realistic blazar-induced pairs. In our simulations, the beam looses only 1% of its energy, and we analytically estimate that the beam would lose its total energy over about 100 simulation times. An analytical scaling is then used to extrapolate the parameters of realistic blazar-induced pair beams. We find that they can dissipate their energy slightly faster by the electrostatic instability than through inverse-Compton scattering. The uncertainties arising from, e.g., details of the primary gamma-ray spectrum are too large to make firm statements for individual blazars, and an analysis based on their specific properties is required. KW - gamma rays: general KW - instabilities KW - magnetic fields KW - relativistic processes KW - waves Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aab552 SN - 0004-637X SN - 1538-4357 VL - 857 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - 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 -