The synchrotron maser emission from relativistic magnetized shocks: Dependence on the pre-shock temperature

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 two-dimensional 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 $\sigma \gtrsim 1$ (i.e., the ratio of incoming Poynting flux to particle energy flux) and thermal spread $\Delta \gamma \equiv kT/m{c}^2=10^{-5}-10^{-1}$. We measure the fraction $f_{\xi }$ of total incoming energy that is converted into precursor waves, as computed in the post-shock frame. At fixed magnetization, we find that $f_{\xi }$ is nearly independent of temperature as long as $\Delta \gamma \lesssim 10^{-1.5}$ (with only a modest decrease of a factor of three from $\Delta \gamma =10^{-5}$ to $\Delta \gamma =10^{-1.5}$), but it drops by nearly two orders of magnitude for $\Delta \gamma \gtrsim 10^{-1}$. At fixed temperature, the scaling with magnetization $f_{\xi }\sim 10^{-3}{\sigma }^{-1}$ is consistent with our earlier one-dimensional results. For our reference $\sigma =1$, the power spectrum of precursor waves is relatively broad (fractional width $\sim 1-3$) for cold temperatures, whereas it shows pronounced line-like features with fractional width $\sim 0.2$ for $10^{-3}\lesssim \Delta \gamma \lesssim 10^{-1.5}$. For $\sigma \gtrsim 1$, the precursor waves are beamed within an angle $\simeq {\sigma }^{-1/2}$ 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.

12 pages, 15 figures, submitted to MNRAS

References in corpus (12)

• Fast Radio Bursts
• Fast radio bursts as synchrotron maser emission from decelerating relativistic blast waves
• INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154
• The magnetic field and turbulence of the cosmic web measured using a brilliant fast radio burst
• A Multi-telescope Campaign on FRB 121102: Implications for the FRB Population
• Simulations of relativistic collisionless shocks: shock structure and particle acceleration
• Implications of a "Fast Radio Burst" from a Galactic Magnetar
• The synchrotron maser emission from relativistic shocks in Fast Radio Bursts: 1D PIC simulations of cold pair plasmas
• Heating and Non-thermal Particle Acceleration in Relativistic, Transverse Magnetosonic Shock Waves in Proton-Electron-Positron Plasmas
• Wakefield Acceleration by Radiation Pressure in Relativistic Shock Waves
• Electron-ion coupling upstream of relativistic collisionless shocks
• A unified picture of Galactic and cosmological fast radio bursts

Cited by in corpus (9)

• Coherent Electromagnetic Emission from Relativistic Magnetized Shocks
• What does FRB light-curve variability tell us about the emission mechanism?
• Mildly relativistic magnetized shocks in electron-ion plasmas -- II. Particle acceleration and heating
• Scintillation can explain the spectral structure of the bright radio burst from SGR 1935+2154
• Filamentation of Fast Radio Bursts in magnetar winds
• Kinetic Simulations of the Filamentation Instability in Pair Plasmas
• Emission Mechanisms of Fast Radio Bursts
• Filamentation of the electromagnetic precursor in relativistic quasi-perpendicular electron-positron shocks
• Superluminal Wave Activation at Relativistic Magnetized Shocks