Constraining the Jet Launching Time of GRB 170817A by Utilizing the Baryon Loading

Abstract

The observed delay of GRB 170817A relative to GW170817 carries significant information about gamma-ray burst (GRB) physics and is subject to intense debate. In this letter, we put forward an approach to discuss the major source of this time delay. First of all, we use the structured jet model to fit the X-ray/optical/radio afterglows of GRB 170817A together with superluminal motion measured by the Very Long Baseline Interferometry. Our structured jet is modelled with angle-dependent energy and baryon loading. It is found that our model can well fit the afterglows of GRB 170817A. After that, the baryon loading in the jet is inferred based on our fitting results. By comparing the baryon loading to the mass outflow in different stages, we infer that the time lag of the jet launch relative to the merger is less than hundreds or tens of milliseconds. It suggests that the time delay of GRB 170817A relative to GW170817 is defined mostly by the spreading time of the jet propagating to its dissipation radius.

13 pages, 4 figures, ApJL accepted

References in corpus (20)

• 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
• 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 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
• A Radio Counterpart to a Neutron Star Merger
• AT2017gfo: an anisotropic and three-component kilonova counterpart of GW170817
• Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817
• Jet collimation in the ejecta of double neutron star merger: new canonical picture of short gamma-ray bursts
• When Did the Remnant of GW170817 Collapse to a Black Hole?
• On the Progenitor of Binary Neutron Star Merger GW170817
• Afterglow Lightcurves from Misaligned Structured Jets
• Lessons from the short GRB170817A - the First Gravitational Wave Detection of a Binary Neutron Star Merger
• Electrons' energy in GRB afterglows implied by radio peaks
• The structure of weakly-magnetized $\gamma$-ray burst jets
• Hyperaccreting Neutron-Star Disks and Neutrino Annihilation
• Constraints on millisecond magnetars as the engines of prompt emission in gamma-ray bursts
• The Delay Time of Gravitational Wave -- Gamma-Ray Burst Associations
• Conditions for jet break-out in NS mergers