Non-thermal emission from mildly relativistic dynamical ejecta of neutron star mergers: spectrum and sky image

Abstract

Binary neutron star mergers are expected to produce fast dynamical ejecta, with mildly relativistic velocities extending to $\beta =v/c>0.6$. In a preceding paper, we derived an analytic description of the time-dependent radio to X-ray synchrotron flux produced by collisionless shocks driven by such fast ejecta into the interstellar medium, for spherical ejecta with broken power-law mass (or energy) distributions, $M(>\gamma \beta )\propto (\gamma \beta {)}^{-s}$ with $s=s_{\text{KN}}$ at $\gamma \beta <{\gamma }_0{\beta }_0$ and $s=s_{\text{ft}}$ at $\gamma \beta >{\gamma }_0{\beta }_0$ (where $\gamma$ is the Lorentz factor). Here, we extend our analysis and provide analytic expressions for the self-absorption frequency, the cooling frequency, and the observed angular size of the emitting region (which appears as a ring in the sky). For parameter values characteristic of merger calculation results -- a "shallow" mass distribution, $1<s_{\text{KN}}<3$, for the bulk of the ejecta (at $\gamma \beta \approx 0.2$), and a steep, $s_{\text{ft}}>5$, "fast tail" mass distribution -- the analytic results reproduce well (to tens of percent accuracy) the results of detailed numeric calculations, a significant improvement over earlier order-of-magnitude estimates (based on extrapolations of results valid for $\gamma \beta \ll 1$).

8 pages, 7 figures, accepted to MNRAS

References in corpus (20)

• The X-ray counterpart to the gravitational wave event GW 170817
• A Radio Counterpart to a Neutron Star Merger
• The Dynamics of Binary Neutron Star Mergers and of GW170817
• The optical afterglow of GW170817 at one year post-merger
• Numerical Relativity Simulations of the Neutron Star Merger GW170817: Long-Term Remnant Evolutions, Winds, Remnant Disks, and Nucleosynthesis
• A thousand days after the merger: continued X-ray emission from GW170817
• Evidence for X-ray Emission in Excess to the Jet Afterglow Decay 3.5 yrs After the Binary Neutron Star Merger GW 170817: A New Emission Component
• Comprehensive study of mass ejection and nucleosynthesis in binary neutron star mergers leaving short-lived massive neutron stars
• Optical measurement of superluminal motion in the neutron-star merger GW170817
• Gamma-ray bursts and collisionless shocks
• Binary neutron star merger simulations with neutrino transport and turbulent viscosity: impact of different schemes and grid resolution
• Continued radio observations of GW170817 3.5 years post-merger
• PIC Simulation Methods for Cosmic Radiation and Plasma Instabilities
• Dynamical ejecta synchrotron emission as possible contributor to the changing behaviour of GRB170817A
• GW170817 4.5 years after merger: Dynamical ejecta afterglow constraints
• Electron Acceleration at Rippled Low-Mach-number Shocks in High-beta Collisionless Cosmic Plasmas
• Mildly relativistic magnetized shocks in electron-ion plasmas -- II. Particle acceleration and heating
• Modeling kilonova afterglows: Effects of the thermal electron population and interaction with GRB outflows
• Non-thermal emission from mildly relativistic dynamical ejecta of neutron star mergers
• Synthetic radio images of structured GRB and kilonova afterglows

Cited by in corpus (5)

• Late-time non-thermal emission from mildly relativistic tidal ejecta of compact objects merger
• Synchrotron break frequencies of mildly-to-highly relativistic outflows observed off-axis
• Numerical Modeling of Relativistic Effects in Synchrotron-Emitting Shocks
• Inferring kilonova ejecta photospheric properties from early blackbody spectra
• The non-thermal emission following GW170817 is consistent with a conical radially-stratified outflow with initial Lorentz factor $\lesssim 10$