On the X-ray, optical and radio afterglows of the BdHN I GRB 180720B generated by the synchrotron emission

TL;DR

This paper models the multi-wavelength afterglows of GRB 180720B, attributing them to synchrotron emission from a newborn neutron star interacting with supernova ejecta, providing insights into the system's physical parameters.

Contribution

It offers a detailed synchrotron emission model explaining the optical, X-ray, and radio afterglows of GRB 180720B, linking them to the newborn neutron star's activity.

Findings

The neutron star's spin powers the afterglows across multiple wavelengths.

Model parameters fit observational data of GRB 180720B.

The interaction between the neutron star and ejecta explains the afterglow evolution.

Abstract

Gamma-ray bursts (GRBs) are systems of unprecedented complexity across all the electromagnetic spectrum, including the radio, optical, X-rays, gamma-rays in the megaelectronvolt (MeV) and gigaelectronvolt (GeV) regime, as well as ultrahigh-energy cosmic rays (UHECRs), each manifested in seven specific physical processes with widely different characteristic evolution timescales ranging from $10^{-14}$ s to $10^{7}$ s or longer. We here study the long GRB 180720B originating from a binary system composed of a massive carbon-oxygen (CO) star of about $10 M_\odot$ and a companion neutron star (NS). The gravitational collapse of the CO star gives rise to a spinning newborn NS ($\nu$NS), with an initial period of $P_0=1$ ms that powers the synchrotron radiation in the radio, optical, and X-ray wavelengths. We here only investigate the GRB 180720B afterglows and present a detailed treatment of its origin based on the synchrotron radiation released by the interaction of the $\nu$NS and the SN ejecta. We show that in parallel to the X-ray afterglow, the spinning $\nu$NS also powers the optical and radio afterglows and allows us to infer the $\nu$NS and ejecta parameters that fit the observational data.