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Title: On the Radio-emitting Particles of the Crab Nebula: Stochastic Acceleration Model

Abstract

The broadband emission of pulsar wind nebulae (PWNe) is well described by non-thermal emissions from accelerated electrons and positrons. However, the standard shock acceleration model of PWNe does not account for the hard spectrum in radio wavelengths. The origin of the radio-emitting particles is also important to determine the pair production efficiency in the pulsar magnetosphere. Here, we propose a possible resolution for the particle energy distribution in PWNe; the radio-emitting particles are not accelerated at the pulsar wind termination shock but are stochastically accelerated by turbulence inside PWNe. We upgrade our past one-zone spectral evolution model to include the energy diffusion, i.e., the stochastic acceleration, and apply the model to the Crab Nebula. A fairly simple form of the energy diffusion coefficient is assumed for this demonstrative study. For a particle injection to the stochastic acceleration process, we consider the continuous injection from the supernova ejecta or the impulsive injection associated with supernova explosion. The observed broadband spectrum and the decay of the radio flux are reproduced by tuning the amount of the particle injected to the stochastic acceleration process. The acceleration timescale and the duration of the acceleration are required to be a few decades and a fewmore » hundred years, respectively. Our results imply that some unveiled mechanisms, such as back reaction to the turbulence, are required to make the energies of stochastically and shock-accelerated particles comparable.« less

Authors:
 [1];  [2]
  1. Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo 658-8501 (Japan)
  2. Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa City, Chiba, 277-8582 (Japan)
Publication Date:
OSTI Identifier:
22663566
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 841; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COMPARATIVE EVALUATIONS; CRAB NEBULA; DECAY; DIFFUSION; EFFICIENCY; ELECTRONS; EMISSION; ENERGY SPECTRA; EVOLUTION; EXPLOSIONS; INJECTION; PAIR PRODUCTION; POSITRONS; PULSARS; RESOLUTION; STELLAR WINDS; STOCHASTIC PROCESSES; TURBULENCE; WAVELENGTHS

Citation Formats

Tanaka, Shuta J., and Asano, Katsuaki, E-mail: sjtanaka@center.konan-u.ac.jp. On the Radio-emitting Particles of the Crab Nebula: Stochastic Acceleration Model. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6F13.
Tanaka, Shuta J., & Asano, Katsuaki, E-mail: sjtanaka@center.konan-u.ac.jp. On the Radio-emitting Particles of the Crab Nebula: Stochastic Acceleration Model. United States. doi:10.3847/1538-4357/AA6F13.
Tanaka, Shuta J., and Asano, Katsuaki, E-mail: sjtanaka@center.konan-u.ac.jp. Thu . "On the Radio-emitting Particles of the Crab Nebula: Stochastic Acceleration Model". United States. doi:10.3847/1538-4357/AA6F13.
@article{osti_22663566,
title = {On the Radio-emitting Particles of the Crab Nebula: Stochastic Acceleration Model},
author = {Tanaka, Shuta J. and Asano, Katsuaki, E-mail: sjtanaka@center.konan-u.ac.jp},
abstractNote = {The broadband emission of pulsar wind nebulae (PWNe) is well described by non-thermal emissions from accelerated electrons and positrons. However, the standard shock acceleration model of PWNe does not account for the hard spectrum in radio wavelengths. The origin of the radio-emitting particles is also important to determine the pair production efficiency in the pulsar magnetosphere. Here, we propose a possible resolution for the particle energy distribution in PWNe; the radio-emitting particles are not accelerated at the pulsar wind termination shock but are stochastically accelerated by turbulence inside PWNe. We upgrade our past one-zone spectral evolution model to include the energy diffusion, i.e., the stochastic acceleration, and apply the model to the Crab Nebula. A fairly simple form of the energy diffusion coefficient is assumed for this demonstrative study. For a particle injection to the stochastic acceleration process, we consider the continuous injection from the supernova ejecta or the impulsive injection associated with supernova explosion. The observed broadband spectrum and the decay of the radio flux are reproduced by tuning the amount of the particle injected to the stochastic acceleration process. The acceleration timescale and the duration of the acceleration are required to be a few decades and a few hundred years, respectively. Our results imply that some unveiled mechanisms, such as back reaction to the turbulence, are required to make the energies of stochastically and shock-accelerated particles comparable.},
doi = {10.3847/1538-4357/AA6F13},
journal = {Astrophysical Journal},
number = 2,
volume = 841,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}