The Identification of Infrared Synchrotron Radiation from Cassiopeia A

Jones, T. J.; Rudnick, Lawrence; DeLaney, Tracey; Bowden, James H.

doi:10.1086/368149

Cited by 40 publications

(44 citation statements)

References 52 publications

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“…The cut-off energy ǫ, the normalization of the spectrum and the value of an interstellar absorption column were allowed to be free parameters. We froze the curvature parameter to a value of 0.06 based on fits to radio and infrared synchrotron data for selected regions of Cas A [38]. A value 5 of a = 0.05 was obtained by our group in fits to SN1006 [39].…”

Section: Creating a Cut-off Frequency Mapmentioning

confidence: 99%

Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant

et al. 2006

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Supernova remnants(SNRs) are believed to be the primary location of the acceleration of Galactic cosmic rays, via diffusive shock (Fermi) acceleration. Despite considerable theoretical work the precise details are still unknown, in part because of the difficulty in directly observing nucleons that are accelerated to TeV energies in, and affect the structure of, the SNR shocks. However, for the last ten years, X-ray observatories ASCA, and more recently Chandra, XMM-Newton, and Suzaku have made it possible to image the synchrotron emission at keV energies produced by cosmic-ray electrons accelerated in the SNR shocks. In this article, we describe a spatially-resolved spectroscopic analysis of Chandra observations of the Galactic SNR Cassiopeia A to map the cutoff frequencies of electrons accelerated in the forward shock. We set upper limits on the diffusion coefficient and find locations where particles appear to be accelerated nearly as fast as theoretically possible (the Bohm limit).Supernova remnants (SNRs) have been established as the leading candidate for the acceleration of cosmic rays. [1][2] It has been shown that the mechanism of diffusive shock acceleration in SNR shocks coupled with some understanding of Galactic transport effects can in theory produce the observed power-law spectrum of cosmic rays. [3]-[10]. This model works at least up to the "knee" of the cosmic ray spectrum near 5 × 10 15 eV, and possibly 1 all the way to the "ankle" near 3×10 18 eV.[11] The charged particles scatter off of irregularities in the magnetic field, increasing their momentum by a fraction of the shock velocity v/c with each round-trip shock crossing. [11] Theoretical work in the last several years has suggested that the process is significantly nonlinear.[10]-[15] Higher energy particles have larger diffusion lengths and therefore sample a greater change in velocity and compression ratio across the shock than lower energy particles. This effect introduces a decrease in the particle distribution's spectral index and a flattening of the spectrum with increasing energy.[10] A smoothing effect on the structure of the shock results, predominantly caused by the ions; electrons are almost "test particles." At high energies the electron spectrum is expected to have the same (curved) spectral shape as the proton spectrum. [10] This correspondence of electron and proton spectra is significant because it is extremely difficult to directly observe the acceleration of cosmic-ray protons in SNR shocks. Their presence is inferred indirectly by detecting π 0 decay γ-rays produced from collisions of the cosmic rays with gas particles in the ambient medium. . Current technology limits the spatial resolution of these instruments to arcminutes and remnants the size of Cas A may appear pointlike. In addition, TeV gamma rays can also be produced by inverse-Compton scattering of cosmic microwave background photons with the accelerated cosmic-ray electrons in SNRs. Consequently, it is difficult to precisely and unambiguously image proton and i...

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Section: Creating a Cut-off Frequency Mapmentioning

confidence: 99%

Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant

et al. 2006

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“…This theory has been tested and confirmed for the Tycho and Kepler SNRs by Reynolds & Ellison (1992). Very recently Jones et al (2003) reported that infrared observations of Cas A also indicate a flattening of the synchrotron spectrum at high frequencies.…”

Section: Cosmic Ray Acceleration and X-ray Synchrotron Emission From mentioning

confidence: 71%

Shocks and particle acceleration in supernova remnants: observational features

Vink

2004

Advances in Space Research

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The last ten years a number of observational advances have substantially increased our knowledge of shock phenomena in supernova remnants. This progress has mainly been made possible by the recent improvements in X-ray and γ-ray instrumentation. It has become clear that some shell-type supernova remnants, e.g. SN 1006, have X-ray emission dominated by synchrotron radiation, proving that electrons are accelerated up to 100 TeV. This is still an order of magnitude below 3 × 10 15 eV, at which energy the ion cosmic ray spectrum at earth shows a spectral break. So one of the major goals is to prove that supernova remnants are capable of accelerating ions at least up that energy. Here I review the evidence that ions and electrons are accelerated up to energies ∼ 100 TeV in supernova remnants, and, in addition, the recent progress that has been made in understanding the physics of collisionless shock fronts and the magnetic fields inside supernova remnants.

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“…A concavity in the spectrum of the radiation generated by relativistic electrons appears to be one of the possible evidences for shock acceleration in the non-linear regime. In the case of supernova remnants, there are hints that this concavity might have been observed [32].…”

Section: Discussion and General Remarksmentioning

confidence: 99%

Particle Acceleration at shocks: some modern aspects of an old problem

Blasi

2004

Nuclear Physics B - Proceedings Supplements

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The acceleration of charged particles at astrophysical collisionless shock waves is one of the best studied processes for the energization of particles to ultrarelativistic energies, required by multifrequency observations in a variety of astrophysical situations. In this paper we discuss some work aimed at describing one of the main progresses made in the theory of shock acceleration, namely the introduction of the non-linear backreaction of the accelerated particles onto the shocked fluid. The implications for the investigation of the origin of ultra high energy cosmic rays will be discussed

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The Identification of Infrared Synchrotron Radiation from Cassiopeia A

Cited by 40 publications

References 52 publications

Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant

Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant

Shocks and particle acceleration in supernova remnants: observational features

Particle Acceleration at shocks: some modern aspects of an old problem

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