GRB~250704B/EP250704a a Short Gamma-Ray Burst Powered by a Magnetar

TL;DR

This paper analyzes a short gamma-ray burst, GRB 250704B, and presents evidence that its prolonged emission and afterglow are powered by a long-lived magnetar undergoing accretion, based on multi-wavelength observations and spectral analysis.

Contribution

It provides the first detailed multi-wavelength analysis linking the extended emission of a short GRB to a magnetar central engine with accretion processes.

Findings

Prolonged X-ray emission is due to magnetar spin-down energy dissipation.

Optical/IR plateau results from synchrotron afterglow with energy injection.

Steep decay phase linked to microphysical parameter changes.

Abstract

GRB~250704B/EP250704a, identified as a short gamma-ray burst (sGRB), exhibited prolonged X-ray emission following the prompt phase and, in optical and infrared (IR) bands, an unusual one-day plateau succeeded by a rapid decline. This sGRB was observed by multiple satellites and ground-based observatories across the electromagnetic spectrum. This study presents temporal and spectral analyses from radio to gamma-ray frequencies, spanning several observation periods beginning after the trigger and continuing for nearly 2 days. The results of the temporal and spectral analyses of the prompt episode, the extended X-ray component, and the afterglow phase are consistent with a millisecond magnetar undergoing accretion. The long-lasting X-ray emission is attributed to the internal energy dissipation of the magnetar spin-down power, governed by the magnetization parameter; the extended optical/IR plateau to synchrotron afterglow emission with energy injection; and the steep decay to changes in microphysical parameters during the post-jet break phase. The X-ray observations are consistent with the superposition of spin-down luminosity and synchrotron afterglow scenario. These findings suggest that the compact-object remnant is most likely a long-lived magnetar.