GRB 170817A Afterglow from a Relativistic Electron-Positron Pair Wind Observed Off-axis

Abstract

A relativistic electron-positron ($e^{+}{e}^{-}$) pair wind from a rapidly rotating, strongly magnetized neutron star (NS) would interact with a gamma-ray burst (GRB) external shock and reshapes afterglow emission signatures. Assuming that the merger remnant of GW170817 is a long-lived NS, we show that a relativistic $e^{+}{e}^{-}$ pair wind model with a simple top-hat jet viewed off-axis can reproduce multi-wavelength afterglow lightcurves and superluminal motion of GRB 170817A. The Markov chain Monte Carlo (MCMC) method is adopted to obtain the best-fitting parameters, which give the jet half-opening angle ${\theta }_j\approx 0.11$ rad, and the viewing angle ${\theta }_v\approx 0.23$ rad. The best-fitting value of ${\theta }_v$ is close to the lower limit of the prior which is chosen based on the gravitational-wave and electromagnetic observations. In addition, we also derive the initial Lorentz factor ${\Gamma }_0\approx 47$ and the isotropic kinetic energy $E_{\mathrm{K},\mathrm{iso}}\approx 2\times 10^{52}\mathrm{erg}$. A consistence between the corrected on-axis values for GRB 170817A and typical values observed for short GRBs indicates that our model can also reproduce the prompt emission of GRB 170817A. An NS with a magnetic field strength $B_p\approx 1.6\times 10^{13}\mathrm{G}$ is obtained in our fitting, indicating that a relatively low thermalization efficiency $\eta \lesssim 10^{-3}$ is needed to satisfy observational constraints on the kilonova. Furthermore, our model is able to reproduce a late-time shallow decay in the X-ray lightcurve and predicts that the X-ray and radio flux will continue to decline in the coming years.

arXiv comment16 pages including 10 figures, accepted for publication in ApJ

References in corpus (66)

• emcee: The MCMC Hammer
• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Multi-messenger Observations of a Binary Neutron Star Merger
• Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
• An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A
• Properties of the binary neutron star merger GW170817
• Origin of the heavy elements in binary neutron-star mergers from a gravitational wave event
• Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
• Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational Wave Event GW170817
• The X-ray counterpart to the gravitational wave event GW 170817
• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817
• Superluminal motion of a relativistic jet in the neutron star merger GW170817
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. I. Dark Energy Camera Discovery of the Optical Counterpart
• A Radio Counterpart to a Neutron Star Merger
• The Fermi GBM Gamma-Ray Burst Spectral Catalog: Four Years Of Data
• Compact radio emission indicates a structured jet was produced by a binary neutron star merger
• A mildly relativistic wide-angle outflow in the neutron star merger GW170817
• Late time afterglow observations reveal a collimated relativistic jet in the ejecta of the binary neutron star merger GW170817
• The Binary Neutron Star event LIGO/VIRGO GW170817 a hundred and sixty days after merger: synchrotron emission across the electromagnetic spectrum
• Optical and X-ray emission from stable millisecond magnetars formed from the merger of binary neutron stars
• The outflow structure of GW170817 from late time broadband observations
• Short GRBs with Extended Emission from Magnetar Birth: Jet Formation and Collimation
• Dissipation in Poynting-flux Dominated Flows: the Sigma-Problem of the Crab Pulsar Wind
• Bright "merger-nova" from the remnant of a neutron star binary merger: A signature of a newly born, massive, millisecond magnetar
• Gamma-Ray Burst Afterglows In The Multi-Messenger Era: Numerical Models and Closure Relations
• GRB efficiency and Possible Physical Processes Shaping the Early Afterglow
• A magnetar origin for the kilonova ejecta in GW170817
• A cocoon shock breakout as the origin of the $\gamma$-ray emission in GW170817
• The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817
• A year in the life of GW170817: the rise and fall of a structured jet from a binary neutron star merger
• How Bad/Good Are the External Forward Shock Afterglow Models of Gamma-Ray Bursts?
• The optical afterglow of GW170817 at one year post-merger
• A Strong Jet Signature in the Late-Time Lightcurve of GW170817
• A Precise Distance to the Host Galaxy of the Binary Neutron Star Merger GW170817 Using Surface Brightness Fluctuations
• Two years of non-thermal emission from the binary neutron star merger GW170817: rapid fading of the jet afterglow and first constraints on the kilonova fastest ejecta
• Relativistic Wind Bubbles and Afterglow Signatures
• Brightening X-ray Emission from GW170817/GRB170817A: Further Evidence for an Outflow
• A long-lived remnant neutron star after GW170817 inferred from its associated kilonova
• A thousand days after the merger: continued X-ray emission from GW170817
• Lessons from the short GRB170817A - the First Gravitational Wave Detection of a Binary Neutron Star Merger
• Smooth Light Curves from a Bumpy Ride: Relativistic Blast Wave Encounters a Density Jump
• The gamma-rays that accompanied GW170817 and the observational signature of a magnetic jet breaking out of NS merger ejecta
• The Afterglow of GRB 990123 and a Dense Medium
• The allowed parameter space of a long-lived neutron star as the merger remnant of GW170817
• Gamma-ray burst jet breaks revisited
• Collimated outflows from long-lived binary neutron star merger remnants
• The Afterglow and Early-Type Host Galaxy of the Short GRB 150101B at z=0.1343
• Hydrodynamics of Relativistic Blast Waves in a Density-Jump Medium and Their Emission Signature
• Shallow decay phase of GRB X-ray afterglows from relativistic wind bubbles
• Measuring the viewing angle of GW170817 with electromagnetic and gravitational waves
• Hyperaccreting Neutron-Star Disks and Neutrino Annihilation
• Hyperaccreting Disks around Magnetars for Gamma-Ray Bursts: Effects of Strong Magnetic Fields
• Magnetar central engine and possible gravitational wave emission of nearby short GRB 160821B
• Continued radio observations of GW170817 3.5 years post-merger
• Hyperaccretion Disks around Neutron Stars
• Imprints of Electron-positron Winds on the Multi-wavelength Afterglows of Gamma-ray Bursts
• The orbit of GW170817 was inclined by less than 28 degrees to the line of sight
• Brightening X-ray/Optical/Radio Emission of GW170817/SGRB 170817A: Results of an Electron-Positron Wind from the Central Engine?
• Optical Transients Powered by Magnetars: Dynamics, Light Curves, and Transition to the Nebular Phase
• GRB 170817A as a Refreshed Shock Afterglow viewed off-axis
• Fallback Accretion Model for the Years-to-Decades X-ray Counterpart to GW170817
• High-energy gamma-ray afterglows from low-luminosity gamma-ray bursts
• Continued Brightening of the Afterglow of GW170817/GRB 170817A as due to a Delayed Energy Injection

Cited by in corpus (4)

• Sciences with the 2.5-meter Wide Field Survey Telescope (WFST)
• Broadband Emission from a Kilonova Ejecta-Pulsar Wind Nebula System: Late-Time X-ray Afterglow Rebrightening of GRB 170817A
• Reverse Shock Emission in an Off-axis Top-hat Jet Model for Gamma-Ray Bursts
• The white dwarf binary merger model of GRB 170817A