[Paper Review] On the conversion of blast wave energy into radiation in active galactic nuclei and gamma-ray bursts

M. Pohl, R. Schlickeiser|arXiv (Cornell University)|Nov 24, 1999

Gamma-ray bursts and supernovae4 citations

TL;DR

This paper proposes that relativistic blast waves in active galactic nuclei (AGN) and gamma-ray bursts (GRBs) convert kinetic energy into radiation via a relativistic two-stream instability that rapidly isotropizes swept-up ambient matter in the blast wave frame, producing relativistic particles without requiring additional acceleration mechanisms. The model successfully reproduces multiwavelength AGN data using only initial conditions, demonstrating that spectral evolution and energy conversion are governed by these parameters alone.

ABSTRACT

It has been suggested that relativistic blast waves may power the jets of AGN and gamma-ray bursts (GRB). We address the important issue how the kinetic energy of collimated blast waves is converted into radiation. It is shown that swept-up ambient matter is quickly isotropised in the blast wave frame by a relativistic two-stream instability, which provides relativistic particles in the jet without invoking any acceleration process. The fate of the blast wave and the spectral evolution of the emission of the energetic particles is therefore solely determined by the initial conditions. We compare our model with existing multiwavelength data of AGN and find remarkable agreement.

Motivation & Objective

• To investigate how kinetic energy in relativistic blast waves is converted into observable radiation in AGN and GRBs.
• To determine whether the formation of relativistic particles in jets can occur without invoking traditional particle acceleration mechanisms.
• To assess whether initial conditions alone can govern the spectral evolution and fate of blast waves in these systems.
• To compare the model's predictions with existing multiwavelength observational data from AGN.

Proposed method

• The study models the dynamics of relativistic blast waves in the context of AGN and GRBs, focusing on energy conversion to radiation.
• It employs the relativistic two-stream instability as the primary mechanism for isotropizing swept-up ambient matter in the blast wave frame.
• The model assumes that particle energization arises intrinsically from the instability, eliminating the need for separate acceleration processes.
• The spectral evolution of emitted radiation is derived from the initial energy distribution and Lorentz factors of the particles generated by the instability.
• The model's predictions are tested against multiwavelength observational data from AGN, including X-ray and radio emissions.
• The analysis focuses on the role of initial conditions—such as shock Lorentz factor and ambient density—in determining the final radiation spectrum.

Experimental results

Research questions

• RQ1 How is kinetic energy in relativistic blast waves efficiently converted into radiation in AGN and GRBs?
• RQ2 Can the formation of relativistic particles in jets occur without invoking standard particle acceleration mechanisms?
• RQ3 To what extent can the spectral evolution of emission be predicted from initial blast wave conditions alone?
• RQ4 How well does the model reproduce observed multiwavelength emission from AGN?

Key findings

• The relativistic two-stream instability efficiently isotropizes swept-up ambient matter in the blast wave frame, generating relativistic particles without requiring external acceleration.
• The model shows that the spectral evolution and radiation output are fully determined by initial conditions, such as shock Lorentz factor and ambient density.
• The predicted emission spectra from the model show remarkable agreement with multiwavelength observations of AGN, particularly in X-ray and radio bands.
• The absence of an external acceleration process simplifies the energy conversion mechanism, making it self-consistent and observationally viable.
• The model successfully explains the broadband emission from AGN jets using only the physics of the blast wave and its interaction with ambient matter.