Radio Afterglow Rebrightening: Evidence for Multiple Active Phases in Gamma-Ray Burst Central Engines

TL;DR

This paper models radio afterglow rebrightenings in gamma-ray bursts as resulting from multiple active phases of the central engine, simulating diverse light curves and fitting observations of GRB 970508.

Contribution

It introduces a novel energy-supply model with multiple active phases of the central engine to explain radio rebrightenings in GRB afterglows.

Findings

Simulated diverse rebrightening light curves with independent physical parameters.

Achieved best fit to GRB 970508 radio afterglow at three frequencies.

Suggests central engine activity longer than typical GRB duration.

Abstract

The rebrightening phenomenon is an interesting feature in some X-ray, optical, and radio afterglows of gamma-ray bursts (GRBs). Here, we propose a possible energy-supply assumption to explain the rebrightenings of radio afterglows, in which the central engine with multiple active phases can supply at least two GRB pulses in a typical GRB duration time. Considering the case of double pulses supplied by the central engine, the double pulses have separate physical parameters, except for the number density of the surrounding interstellar medium (ISM). Their independent radio afterglows are integrated by the ground detectors to form the rebrightening phenomenon. In this work, we firstly simulate diverse rebrightening light curves under consideration of different and independent physical parameters. Using this assumption, we also give our best fit to the radio afterglow of GRB 970508 at three frequencies of 1.43, 4.86, and 8.46 GHz. We suggest that the central engine may be active continuously at a timescale longer than that of a typical GRB duration time as many authors have suggested, and that it may supply enough energy to cause the long-lasting rebrightenings observed in some GRB afterglows.