Shock within a shock: revisiting the radio flares of NS merger ejecta and GRB-supernovae

Abstract

Fast ejecta expelled in binary neutron star (NS) mergers or energetic supernovae (SNe) should produce late-time synchrotron radio emission as the ejecta shocks into the surrounding ambient medium. Models for such radio flares typically assume the ejecta expands into an unperturbed interstellar medium (ISM). However, it is also well-known that binary NS mergers and broad-lined Ic SNe can harbor relativistic jetted outflows. In this work, we show that such jets shock the ambient ISM ahead of the ejecta, thus evacuating the medium into which the ejecta subsequently collides. Using an idealized spherically-symmetric model, we illustrate that this inhibits the ejecta radio flare at early times $t<t_{\mathrm{col}}\approx 12\mathrm{yr}(E_{\mathrm{j}}/10^{49}\mathrm{erg}{)}^{1/3}(n/1{\mathrm{cm}}^{-3}{)}^{-1/3}(v_{\mathrm{ej}}/0.1c{)}^{-5/3}$ where $E_{\mathrm{j}}$ is the jet energy, $n$ the ISM density, and $v_{\mathrm{ej}}$ the ejecta velocity. We also show that this can produce a sharply peaked enhancement in the light-curve at $t=t_{\mathrm{col}}$. This has implications for radio observations of GW170817 and future binary NS mergers, gamma-ray burst (GRB) SNe, decade-long radio transients such as FIRST J1419, and possibly other events where a relativistic outflow precedes a slower-moving ejecta. Future numerical work will extend these analytic estimates and treat the multi-dimensional nature of the problem.

submitted to MNRAS; comments welcome!

References in corpus (25)

• Multi-messenger Observations of a Binary Neutron Star Merger
• The Supernova -- Gamma-Ray Burst Connection
• Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. II. UV, Optical, and Near-IR Light Curves and Comparison to Kilonova Models
• The X-ray counterpart to the gravitational wave event GW 170817
• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two Neutron Stars
• The Combined Ultraviolet, Optical, and Near-Infrared Light Curves of the Kilonova Associated with the Binary Neutron Star Merger GW170817: Unified Data Set, Analytic Models, and Physical Implications
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. V. Rising X-ray Emission from an Off-Axis Jet
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-Time Emission from the Kilonova Ejecta
• A Deep Chandra X-ray Study of Neutron Star Coalescence GW170817
• The Observable Signatures of GRB Cocoons
• The Dynamics and Afterglow Radiation of Gamma-Ray Bursts. I. Constant Density Medium
• Non-Thermal Electron Acceleration in Low Mach Number Collisionless Shocks. I. Particle Energy Spectra and Acceleration Mechanism
• Mass ejection from neutron star mergers: different components and expected radio signals
• Non-Thermal Electron Acceleration in Low Mach Number Collisionless Shocks. II. Firehose-Mediated Fermi Acceleration and its Dependence on Pre-Shock Conditions
• Sub-radian-accuracy gravitational waveforms of coalescing binary neutron stars in numerical relativity
• Forming a constant density medium close to long gamma-ray bursts
• Radio Constraints on Long-Lived Magnetar Remnants in Short Gamma-Ray Bursts
• Electron Preacceleration in Weak Quasi-perpendicular Shocks in High-beta Intracluster Medium
• Observable Features of GW170817 Kilonova Afterglow
• A Search for Late-Time Radio Emission and Fast Radio Bursts from Superluminous Supernovae
• Constraining the long-lived magnetar remnants in short gamma-ray bursts from late-time radio observations
• Resolving the decades-long transient FIRST J141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula?
• Observational Constraints on Late-Time Radio Rebrightening of GRB-Supernovae

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• 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
• Continued radio observations of GW170817 3.5 years post-merger
• Dynamical ejecta synchrotron emission as possible contributor to the changing behaviour of GRB170817A
• A Late-time Radio Survey of Short GRBs at $z<0.5$: New Constraints on the Remnants of Neutron Star Mergers
• Thermal Electrons in Mildly-relativistic Synchrotron Blast-waves
• Searching for the radio remnants of short duration gamma-ray bursts
• Late-Time Radio and Millimeter Observations of Superluminous Supernovae and Long Gamma Ray Bursts: Implications for Obscured Star Formation, Central Engines, and Fast Radio Bursts
• On the diversity of magnetar-driven kilonovae
• GW170817 4.5 years after merger: Dynamical ejecta afterglow constraints
• Electromagnetic counterparts of binary neutron star mergers leading to a strongly magnetized long-lived remnant neutron star
• The large landscape of supernova, GRB and cocoon interactions
• Late-time radio observations of the short GRB200522A: constraints on the magnetar model
• Modeling kilonova afterglows: Effects of the thermal electron population and interaction with GRB outflows
• Late-Time Evolution and Modeling of the Off-Axis Gamma-ray Burst Candidate FIRST J141918.9+394036
• Radio Afterglows from Compact Binary Coalescences: Prospects for Next-Generation Telescopes
• Afterglow light curves of the non-relativistic ejecta mass in a stratified circumstellar medium
• Multi-Peaked Non-Thermal Light Curves from Magnetar-Powered Gamma-Ray Bursts
• Synthetic radio images of structured GRB and kilonova afterglows
• Search for radio remnants of nearby off-axis Gamma-Ray Bursts in a sample of Swift/BAT events
• Radio Constraints on $r$-process Nucleosynthesis by Collapsars
• VLT/MUSE and ATCA observations of the host galaxy of the short GRB 080905A at z=0.122
• GRB Afterglow of the Sub-relativistic Materials with Energy Injection
• Features and prospects for kilonova remnant detection with current and future surveys
• Accurate flux calibration of GW170817: is the X-ray counterpart on the rise?
• Numerical Modeling of Relativistic Effects in Synchrotron-Emitting Shocks
• Signatures of deconfined quark phases in binary neutron star mergers