The afterglow emission from a stratified jet in GRB 170817A

Abstract

The afterglow of GRB 170817A has been detected for more than three years, but the origin of the multi-band afterglow light curves remains under debate. A classical top-hat jet model is faced with difficulties in producing a shallow rise of the afterglow light curves as observed $(F_{\nu }\propto T^{0.8})$. Here we reconsider the model of stratified ejecta with energy profile of $E(>\Gamma \beta )=E_0(\Gamma \beta {)}^{-k}$ as the origin of the afterglow light curves of the burst, where $\Gamma$ and $\beta$ are the Lorentz factor and speed of the ejecta, respectively. $k$ is the power-law slope of the energy profile. We consider the ejecta are collimated into jets. Two kinds of jet evolutions are investigated, including a lateral-spreading jet and a non-lateral-spreading jet. We fit the multi-band afterglow light curves, including the X-ray data at one thousand days post-burst, and find that both the models of the spreading and non-spreading jets can fit the light curves well, but the observed angular size of the source and the apparent velocity of the flux centroid for the spreading jet model are beyond the observation limits, while the non-spreading jet model meets the observation limits. Some of the best-fit parameters for the non-spreading jet model, such as the number density of the circumburst medium $\sim 10^{-2}$ cm${}^{-3}$ and the total jet kinetic energy $E\sim 4.8\times 10^{51}$ erg, also appear plausible. The best-fit slope of the jet energy profile is $k\sim 7.1$. Our results suggest that the afterglow of GRB 170817A may arise from the stratified jet and that the lateral spreading of the jet is not significant.

16 pages, 5 figures, 1 table. Accepted for publication in RAA

References in corpus (14)

• Multi-messenger Observations of a Binary Neutron Star Merger
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• The X-ray counterpart to the gravitational wave event GW 170817
• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger
• A Radio Counterpart to a Neutron Star Merger
• 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 Dynamics and Afterglow Radiation of Gamma-Ray Bursts. I. Constant Density Medium
• The optical afterglow of GW170817 at one year post-merger
• Observational Signatures of High-Energy Emission during the Shallow Decay Phase of GRB X-Ray Afterglows
• GRB 170817A as a Refreshed Shock Afterglow viewed off-axis
• Self-similar solutions for the interaction of relativistic ejecta with an ambient medium

Cited by in corpus (2)

• A global test of jet structure and delay time distribution of short-duration gamma-ray bursts
• Revise thermal winds of remnant neutron stars in gamma-ray bursts