scholarly journals The synchrotron maser emission from relativistic magnetized shocks: dependence on the pre-shock temperature

2020 ◽  
Vol 499 (2) ◽  
pp. 2884-2895 ◽  
Author(s):  
Aliya-Nur Babul ◽  
Lorenzo Sironi

ABSTRACT Electromagnetic precursor waves generated by the synchrotron maser instability at relativistic magnetized shocks have been recently invoked to explain the coherent radio emission of fast radio bursts. By means of 2D particle-in-cell simulations, we explore the properties of the precursor waves in relativistic electron–positron perpendicular shocks as a function of the pre-shock magnetization σ ≳ 1 (i.e. the ratio of incoming Poynting flux to particle energy flux) and thermal spread Δγ ≡ kT/mc2 = 10−5−10−1. We measure the fraction fξ of total incoming energy that is converted into precursor waves, as computed in the post-shock frame. At fixed magnetization, we find that fξ is nearly independent of temperature as long as Δγ ≲ 10−1.5 (with only a modest decrease of a factor of 3 from Δγ = 10−5 to Δγ = 10−1.5), but it drops by nearly two orders of magnitude for Δγ ≳ 10−1. At fixed temperature, the scaling with magnetization $f_\xi \sim 10^{-3}\, \sigma ^{-1}$ is consistent with our earlier 1D results. For our reference σ = 1, the power spectrum of precursor waves is relatively broad (fractional width ∼1 − 3) for cold temperatures, whereas it shows pronounced line-like features with fractional width ∼0.2 for 10−3 ≲ Δγ ≲ 10−1.5. For σ ≳ 1, the precursor waves are beamed within an angle ≃σ−1/2 from the shock normal (as measured in the post-shock frame), as required so they can outrun the shock. Our results can provide physically grounded inputs for FRB emission models based on maser emission from relativistic shocks.

2019 ◽  
Vol 485 (3) ◽  
pp. 3816-3833 ◽  
Author(s):  
Illya Plotnikov ◽  
Lorenzo Sironi

ABSTRACT The emission process of Fast Radio Bursts (FRBs) remains unknown. We investigate whether the synchrotron maser emission from relativistic shocks in a magnetar wind can explain the observed FRB properties. We perform particle-in-cell (PIC) simulations of perpendicular shocks in cold pair plasmas, checking our results for consistency among three PIC codes. We confirm that a linearly polarized X-mode wave is self-consistently generated by the shock and propagates back upstream as a precursor wave. We find that at magnetizations σ ≳ 1 (i.e. ratio of Poynting flux to particle energy flux of the pre-shock flow) the shock converts a fraction $f_\xi ^{\prime } \approx 7 \times 10^{-4}/\sigma ^2$ of the total incoming energy into the precursor wave, as measured in the shock frame. The wave spectrum is narrow-band (fractional width ≲1−3), with apparent but not dominant line-like features as many resonances concurrently contribute. The peak frequency in the pre-shock (observer) frame is $\omega ^{\prime \prime }_{\rm peak} \approx 3 \gamma _{\rm s | u} \omega _{\rm p}$, where γs|u is the shock Lorentz factor in the upstream frame and ωp the plasma frequency. At σ ≳ 1, where our estimated $\omega ^{\prime \prime }_{\rm peak}$ differs from previous works, the shock structure presents two solitons separated by a cavity, and the peak frequency corresponds to an eigenmode of the cavity. Our results provide physically grounded inputs for FRB emission models within the magnetar scenario.


2021 ◽  
Vol 2 (2) ◽  
pp. 18-25
Author(s):  
Ananthanarasimhan J ◽  
Anand M.S. ◽  
Lakshminarayana R

This work presents simple numerical simulation algorithm to analyse the velocity evolution of high density non-magnetized glow discharge (cold) collision-less plasma using Particle-in-Cell (PIC) method. In the place of millions of physical electrons and background ions, fewer particles called super particles are used for simulation to capture the plasma properties such as particle velocity, particle energy and electrical field of the plasma system. The plasma system which is of interest in this work is weakly coupled plasma having quasi-neutrality nature. Simulation results showed symmetric velocity distribution about zero with slight left skewness, indicating static system. The order of directional velocity of individual particle seems to agree with the input electron temperature of the considered plasma system. The particle and field energy evolution were observed having fluctuations about zero which indicates that the system is equilibrating. This work marks the preliminary work to study the transport of plasma species in plasma column of gliding arc discharge.


2020 ◽  
Vol 235 ◽  
pp. 07003
Author(s):  
Yingchao Lu ◽  
Fan Guo ◽  
Patrick Kilian ◽  
Hui Li ◽  
Chengkun Huang ◽  
...  

A rotating pulsar creates a surrounding pulsar wind nebula (PWN) by steadily releasing an energetic wind into the interior of the expanding shockwave of supernova remnant or interstellar medium. At the termination shock of a PWN, the Poynting-flux- dominated relativistic striped wind is compressed. Magnetic reconnection is driven by the compression and converts magnetic energy into particle kinetic energy and accelerating particles to high energies. We carrying out particle-in-cell (PIC) simulations to study the shock structure as well as the energy conversion and particle acceleration mechanism. By analyzing particle trajectories, we find that many particles are accelerated by Fermi-type mechanism. The maximum energy for electrons and positrons can reach hundreds of TeV.


2007 ◽  
Vol 25 (6) ◽  
pp. 1345-1358 ◽  
Author(s):  
V. G. Merkin ◽  
J. G. Lyon ◽  
B. J. Anderson ◽  
H. Korth ◽  
C. C. Goodrich ◽  
...  

Abstract. We show results of the Lyon-Fedder-Mobarry (LFM) global MHD simulations of an event previously examined using Iridium spacecraft observations as well as DMSP and IMAGE FUV data. The event is chosen for the steady northward IMF sustained over a three-hour period during 16 July 2000. The Iridium observations showed very weak or absent Region 2 currents in the ionosphere, which makes the event favorable for global MHD modeling. Here we are interested in examining the model's performace during weak magnetospheric forcing, in particular, its ability to reproduce gross signatures of the ionospheric currents and convection pattern and energy deposition in the ionosphere both due to the Poynting flux and particle precipitation. We compare the ionospheric field-aligned current and electric potential patterns with those recovered from Iridium and DMSP observations, respectively. In addition, DMSP magnetometer data are used for comparisons of ionospheric magnetic perturbations. The electromagnetic energy flux is compared with Iridium-inferred values, while IMAGE FUV observations are utilized to verify the simulated particle energy flux.


2008 ◽  
Vol 17 (10) ◽  
pp. 1803-1809 ◽  
Author(s):  
M. A. RIQUELME ◽  
A. SPITKOVSKY

We study the current-driven instability predicted by Bell (2004) using particle-in-cell simulations. We use one-dimensional simulations to test the dispersion relation and the nonlinear properties of the instability for the case of a relativistic shock front under idealized conditions. We find that if the cosmic rays (CR) are energetic enough to not get deflected by the generated magnetic field, the instability can grow exponentially until the Alfvén velocity of the plasma becomes comparable to the speed of light. We also use one- and two-dimensional simulations to study the effect of the back reaction of the instability on CR. We find that the deflection and filamentation of CR and background plasma play an important role in the saturation of the instability. The current-driven instability is a viable mechanism for the amplification of magnetic fields in both non-relativistic and relativistic shock environments.


2016 ◽  
Vol 82 (1) ◽  
Author(s):  
A. E. Turrell ◽  
M. Sherlock ◽  
S. J. Rose

Particle-based simulations, such as in particle-in-cell (PIC) codes, are widely used in plasma physics research. The analysis of particle energy transfers, as described by the second moment of the Boltzmann equation, is often necessary within these simulations. We present computationally efficient, analytically derived equations for evaluating collisional energy transfer terms from simulations using discrete particles. The equations are expressed as a sum over the properties of the discrete particles.


2012 ◽  
Vol 08 ◽  
pp. 144-150 ◽  
Author(s):  
LORENZO SIRONI ◽  
ANATOLY SPITKOVSKY

The relativistic wind of pulsars consists of toroidal stripes of opposite magnetic field polarity, separated by current sheets of hot plasma. By means of multi-dimensional particle-in-cell simulations, we investigate particle acceleration and magnetic field dissipation at the termination shock of a relativistic striped pulsar wind. At the shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength λ or the wind magnetization σ (in the regime σ ≫1 of magnetically dominated flows), shock-driven reconnection transfers all the magnetic energy of alternating fields to the particles. In the limit λ/(rL σ) ≫ 1, where rL is the relativistic Larmor radius in the wind, the post-shock spectrum approaches a flat power-law tail with slope around -1.5, populated by particles accelerated by the reconnection electric field. Our findings place important constraints on the models of non-thermal radiation from Pulsar Wind Nebulae.


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