Radiative Processes in Relativistic Astrophysical Plasmas

Yonggang Luo, Purdue University

Abstract

Syncheotron radiation and inverse Compton (IC) svatecring are the two mest ewential radiation mechanisms in high energy astrophysics Synchroteon cediation typically dominates lower energy einision, up to GeV, and IC scattering dominates higher energy gamma-ray emission. In this wart. radiation codex are developed to calculate broadband synchrotron and IC spectra Sor relativistic astrophysical surces: Pubar Wind Nebulae (PAWNe) and Gamma-Ray Bursts (GRBs). Our colmst cadia- tion code takes into account varying intrinsic plasma propesties (€.9.. magnetic fiekd volition}, various inverse Compton processes (synchrotron self-Compton and exter- nal Campton} while accounting for Kiein-Nishina effects. ax well as cedativixtic bulk inution of the emitting plasmin.First, we develop a tarbulent model of the most important higher cuergy astro. physical snurve, the Crab Nebula. The model rims to cesotve several long-standing problems of (PY 'Ne): (i) the sigma problem: (ii) the hard spectrum of radio electrons: (iii the high peak energy of guinma-cay Aares: (ix) and the spatial evolution of the infrared (1R) esnission. The Nebula contains two populations of injected particies: Companent-1 accelerated at the wind termination shock via Fermi-? mechanise. and Component-II accelerated ia reconnecting turbulence in highty magnetized (sigma 2 1) plasmas in the central past of the Crmb Nebula. The reconnecting turbulence ‘(Component-II extends fram radio to gamma rays. In emence. it aceclerates radio eles. trons with a hard spectrum. destroving in the provess the large scale magnetic flux (and thas resolves the signe-problem), and accnsionally prodnces gamens-my flares (rom the largest scale reconnection events). The model reproduces the broadband spectrum of the Crab Nebula, from low-frequency synchrotron emission in radio to inverse-Compton emission at TeY energies, as well as spatially resolved evolution of the spectral indices in IR and optical bands.Second, we study the afterglows of GRBs, concentrating on the unusual temporal features observed in some GRBs (¢.g.. GRB 070110): flares. plateaus, and sudden drops in intensity. These variations are hard to explain with the standard madel that amociates the afterglow emission with the forward shock. We advance the model of afterglows of GRBs with a dominant contribution from the reverse shock propagating in an ultra-relativistic, highly-magnetized long-lasting wind produced by the central engine, presumably a powerful pulsar. We demonstrate that mild variations in the wind luminosity can produce afterglow flares, while sudden steep decay is due to the sudden termination of wind (e.g., due to the collapse of the central object into the black hole}. Finally, we study the finit gravitational wave observation accompanied by the elec- tromagnetic signal, GW/GRB 170817. In this event, the LIGO and Virgo detectors observed a gravitational wave signal followed by a short gamma-ray bunit. We caleu- lated the afterglow emission within a cocoon-jet paradigm and predicted the second bump in the afterglow of GRB 170817.

Degree

Ph.D.

Advisors

Lyutikov, Purdue University.

Subject Area

Energy|Atomic physics|Electromagnetics|Physics

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