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.

16 pages including 10 figures, accepted for publication in ApJ

References in corpus (23)

• 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
• 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
• 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
• 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 Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817
• The optical afterglow of GW170817 at one year post-merger
• Brightening X-ray Emission from GW170817/GRB170817A: Further Evidence for an Outflow
• 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 Afterglow and Early-Type Host Galaxy of the Short GRB 150101B at z=0.1343
• Hyperaccreting Neutron-Star Disks and Neutrino Annihilation
• Magnetar central engine and possible gravitational wave emission of nearby short GRB 160821B
• Hyperaccretion Disks around Neutron Stars
• GRB 170817A as a Refreshed Shock Afterglow viewed off-axis

Cited by in corpus (3)

• 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