Magnetohydrodynamics of Magnetars' High-Energy And Radio Emissions: A Simulation Study

Riddhi Mehta, Purdue University

Abstract

This article-based dissertation provides a review on the broad subject of magnetars - their characteristics, giant flares (GFs) and associated observations of X-ray, γ-ray, and radio emissions and their proposed physical mechanisms. The primary purpose of this dissertation is to provide an extensive description of the two research projects I undertook during my tenure as a Graduate Research Assistant, under the guidance of my advisor. Broadly, my research was focused on building analytical models and running three-dimensional (3-D), high-resolution magnetohydrodynamic (MHD) simulations using the astrophysical PLUTO code to investigate the physical mechanisms behind high-energy (X-ray and γ-ray) and radio emissions associated with magnetar GFs using observational constraints. This, in turn, aided in either validating or disfavoring existing theories behind such energetic explosions. Chapter 1 . provides a review on magnetars, their GFs and associated high-energy and radio emissions, largely based on excellent reviews by [1 . ]–[5 . ]. I summarize interesting observational features of magnetars, specifically those of soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs), along with known aspects of their X-ray and γ-ray activity. I focus on the December 27, 2004 GF emitted by SGR 1806-20, the most energetic GF out of the three that occurred to date, describe its energetics and summarize existing theories behind the physical mechanisms that give rise to two emission characteristics associated with the GF - (i) quasi-periodic oscillations (QPOs) seen in the tail, and (ii) a radio afterglow detected a week after the GF. Lastly, I describe the methods I used to hypothesize the physical mechanisms behind QPOs and the radio emission and compare and contrast them with those suggested previously. In chapter 2 . , I present a version of the research article in preparation and pending publication in the Monthly Notices of the Royal Astronomical Society. The work titled “Radio afterglow of magnetars’ giant flares”, undertaken under the supervision of Dr. Maxim Lyutikov and in collaboration with Dr. Maxim Barkov, explores the possible physical mechanisms behind the radio afterglow associated with the SGR 1806-20 GF using high-resolution 3-D MHD simulations.

Degree

Ph.D.

Advisors

Lyutikov, Purdue University.

Subject Area

Energy|Astronomy|Astrophysics|Electromagnetics|Physics

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