Electron density power spectrum in the local interstellar medium

Armstrong, J. W.; Rickett, B. J.; Spangler, S. R.

doi:10.1086/175515

Cited by 909 publications

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“…We derived this estimate based on the Goodman & Narayan (2006) fitting formula for ISS, assuming fiducial values of the scattering screen distance (500 pc), scattering screen velocity (30 km s −1 ), and transition frequency between weak and strong scattering (5 GHz). We also assume that the power spectrum of the electron density fluctuations in the ISM follow a power law consistent with Kolmogorov turbulence; this is observationally motivated (Armstrong et al 1995). At the mean redshift of z ∼ 1 for our M ∩ R sample, sources exhibiting ISS at amplitudes of m5 ≥ 0.02 are thus expected to have components with linear sizes of 1 pc.…”

Section: Interpretation As Interdependence Between Iss and Intrinsic mentioning

confidence: 99%

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

Koay

Macquart

Jauncey

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate the relationship between 5 GHz interstellar scintillation (ISS) and 15 GHz intrinsic variability of compact, radio-selected AGNs drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory (OVRO) blazar monitoring program. We discover that the strongest scintillators at 5 GHz (modulation index, m 5 ≥ 0.02) all exhibit strong 15 GHz intrinsic variability (m 15 ≥ 0.1). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at ∼ 100 µas scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5 GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15 GHz variability amplitudes, most likely due to jet opacity effects.

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Section: Interpretation As Interdependence Between Iss and Intrinsic mentioning

confidence: 99%

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

Koay

Macquart

Jauncey

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Studies of power spectra resulted in substantial progress of our understanding of interstellar turbulence. For instance, the Big Power Law in the Sky (Armstrong et al 1995;Chepurnov & Lazarian 2010), as well as studies of random densities (see Elmegreen & Scalo 2004, for a review) and velocities (see Lazarian 2009 for a review; Chepurnov et al 2015), provided convincing evidence for the existence and importance of turbulence in the interstellar media.…”

Section: Discussionmentioning

confidence: 99%

The Phase Coherence of Interstellar Density Fluctuations

Burkhart

Lazarían

2016

ApJ

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Studies of MHD turbulence often investigate the Fourier power spectrum to provide information on the nature of the turbulence cascade. However, the Fourier power spectrum only contains the Fourier amplitudes and rejects all information regarding the Fourier phases. Here, we investigate the utility of two statistical diagnostics for recovering information on Fourier phases in ISM column density maps: the averaged amplitudes of the bispectrum and the phase coherence index (PCI), a new phase technique for the ISM. We create three-dimensional density and two-dimensional column density maps using a set of simulations of isothermal ideal MHD turbulence with a wide range of sonic and Alfvénic Mach numbers. We find that the bispectrum averaged along different angles with respect to either the k 1 or k 2 axis is primarily sensitive to the sonic Mach number while averaging the bispectral amplitudes over different annuli is sensitive to both the sonic and Alfvénic Mach numbers. The PCI of density suggests that the most correlated phases occur in supersonic sub-Alfvénic turbulence and near the shock scale. This suggests that nonlinear interactions with correlated phases are strongest in shock-dominated regions, in agreement with findings from the solar wind. Our results suggest that the phase information contained in the bispectrum and PCI can be used to find the turbulence parameters in column density maps.

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“…Compilations of pulsar scattering observations reveal that, in some average sense, the power spectrum of electron density fluctuations in the ISM follows a power law on scales from ∼ 10 6 m up to 10 14−18 m, with a power-law index close to 11/3, the value expected from Kolmogorov turbulence (Armstrong, Rickett & Spangler 1995). In the Kolmogorov view of turbulence, mechanical and magnetic energy from macroscopic processes, such as stellar winds and explosions, cascades to smaller scales via a succession of self-similar kinetic-energy conserving turbulent eddies.…”

Section: Why Bother About Turbulence?mentioning

confidence: 93%

Interstellar scattering — New diagnostics of pulsars and the ISM

Macquart¹

2012

Proc. IAU

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Abstract. Extreme Scattering Events and pulsar secondary spectra have highlighted fundamental problems in our understanding of the dynamics of interstellar turbulence. We describe some of these problems in detail and present the theory behind the technique of speckle imaging, which offers a prospect of revealing fundamental properties of the turbulence. It also offers the prospect of resolving pulsar magnetospheres on ∼ 10 nas scales.

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Electron density power spectrum in the local interstellar medium

Cited by 909 publications

References 0 publications

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

The Phase Coherence of Interstellar Density Fluctuations

Interstellar scattering — New diagnostics of pulsars and the ISM

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