Radiative transfer simulations of magnetar flare beaming

TL;DR

This paper introduces a numerical model simulating magnetar flare emission beaming, demonstrating that relativistic outflows are essential to reproduce observed pulse profiles and modulations.

Contribution

The study presents a new simulation approach for magnetar flare beaming, emphasizing the role of relativistic outflows in shaping observed pulse characteristics.

Findings

Relativistic outflows are crucial for matching observed pulse fractions.

The model reproduces sharp peaks in magnetar flare profiles.

Without outflows, beaming is inadequate to explain modulations.

Abstract

Magnetar giant flares show oscillatory modulations in the tails of their light curves, which can only be explained via some form of beaming. The fireball model for magnetar bursts has been used successfully to fit the phase-averaged light curves of the tails of giant flares, but so far no attempts have been made to fit the pulsations. We present a relatively simple numerical model to simulate beaming of magnetar flare emission. In our simulations, radiation escapes from the base of a fireball trapped in a dipolar magnetic field, and is scattered through the optically thick magnetosphere of the magnetar until it escapes. Beaming is provided by the presence of a relativistic outflow, as well as by the geometry of the system. We find that a simple picture for the relativistic outflow is enough to create the pulse fraction and sharp peaks observed in pulse profiles of magnetar flares, while without a relativistic outflow the beaming is insufficient to explain giant flare rotational modulations.