Scattering analysis of LOFAR pulsar observations

Geyer, M.; Karastergiou, A.; Kondratiev, V. I.; Zagkouris, K.; Krämer, M.; Stappers, B. W.; Grießmeier, Jean-Mathias; Hessels, J. W. T.; Michilli, D.; Pilia, M.; Sobey, C.

doi:10.1093/mnras/stx1151

Cited by 82 publications

(90 citation statements)

References 63 publications

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“…Also shown are power law fits of the form τ ∝ ν α . For the thin screen model we obtain α = −2.5 ± 0.6, which is well in agreement with the measurements of Lewandowski et al (2015, α = −2.52 ± 0.3) but lower than those of Geyer et al (2017) who measure α = −3.8 ± 0.4. The use of the thick screen model, yields a slightly higher α = −2.9 ± 0.7, which agrees with the thin-screen-estimate within the uncertainties.…”

Section: Psr J0742−2822supporting

confidence: 92%

Probing Pulsar Scattering between 120 and 280 MHz with the MWA

Kirsten

Bhat

Meyers

et al. 2019

ApJ

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The high sensitivity and wide frequency coverage of the Murchison Widefield Array allow for the measurement of the spectral scaling of the pulsar scattering timescale, α, from a single observation. Here we present three case studies targeted at bright, strongly scattered pulsars J0534+2200 (the Crab pulsar), J0835−4510 (the Vela pulsar) and J0742−2822. We measure the scattering spectral indices to be −3.8 ± 0.2, −4.0 ± 1.5, and −2.5 ± 0.6 for the Crab, Vela, and J0742−2822, respectively. We find that the scattered profiles of both Vela and J0742−2822 are best described by a thin screen model where the Gum Nebula likely contributes most of the observed scattering delay. For the Crab pulsar we see characteristically different pulse shapes compared to higher frequencies, for which none of the scattering screen models we explore are found to be optimal. The presence of a finite inner scale to the turbulence can possibly explain some of the discrepancies.

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Section: Psr J0742−2822supporting

confidence: 92%

Probing Pulsar Scattering between 120 and 280 MHz with the MWA

Kirsten

Bhat

Meyers

et al. 2019

ApJ

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“…They are characterized by an asymmetric profile, with a sharp rise and a slower, typically exponential, decay; the asymmetry becomes larger as the exponential decay time becomes larger. Such temporal characteristics share many similarities with those of radio pulsars observed with, e.g., LOFAR (Geyer et al 2017). Since angular scattering of photons relative to the line of sight leads to different travel distances (Williamson 1972) and hence arrival times at the observer, this suggests that a common scattering process can explain both the angular size and the time profile of solar radio bursts.…”

Section: Introductionsupporting

confidence: 54%

A Fokker–Planck Framework for Studying the Diffusion of Radio Burst Waves in the Solar Corona

Bian

Emslie

Kontar

2019

ApJ

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Electromagnetic wave scattering off density inhomogeneities in the solar corona is an important process which determines both the apparent source size and the time profile of radio bursts observed at 1 AU. Here we model the scattering process using a Fokker-Planck equation and apply this formalism to several regimes of interest. In the first regime the density fluctuations are considered quasi-static and diffusion in wavevector space is dominated by angular diffusion on the surface of a constant energy sphere. In the small-angle ("pencil beam") approximation, this diffusion further occurs over a small solid angle in wavevector space. The second regime corresponds to a much later time, by which scattering has rendered the photon distribution near-isotropic resulting in a spatial diffusion of the radiation. The third regime involves time-dependent fluctuations and, therefore, Fermi acceleration of photons. Combined, these results provide a comprehensive theoretical framework within which to understand several important features of propagation of radio burst waves in the solar corona: emitted photons are accelerated in a relatively small inner region and then diffuse outwards to larger distances. En route, angular diffusion results both in source sizes which are substantially larger than the intrinsic source, and in observed intensity-versus-time profiles that are asymmetric, with a sharp rise and an exponential decay. Both of these features are consistent with observations of solar radio bursts.

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“…This observed limit is close to what one would expect from pulse profile broadening due to scattering. This is true when using either the Bhat et al (2004) or Geyer et al (2017) scattering versus DM relations. The cumulative histograms of the spin period distribution of the pulsars discovered and redetected in the survey (Fig.…”

Section: Discovery Parameter Spacementioning

confidence: 99%

The LOFAR Tied-Array All-Sky Survey (LOTAAS): Survey overview and initial pulsar discoveries

Sanidas

Cooper

Bassa

et al. 2019

A&A

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110

132

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We present an overview of the LOFAR Tied-Array All-Sky Survey (LOTAAS) for radio pulsars and fast transients. The survey uses the high-band antennas of the LOFAR Superterp, the dense inner part of the LOFAR core, to survey the northern sky (δ > 0 • ) at a central observing frequency of 135 MHz. A total of 219 tied-array beams (coherent summation of station signals, covering 12 square degrees), as well as three incoherent beams (covering 67 square degrees) are formed in each survey pointing. For each of the 222 beams, total intensity is recorded at 491.52 µs time resolution. Each observation integrates for 1 hr and covers 2592 channels from 119 to 151 MHz. This instrumental setup allows LOTAAS to reach a detection threshold of 1 to 5 mJy for periodic emission. Thus far, the LOTAAS survey has resulted in the discovery of 73 radio pulsars. Among these are two mildly recycled binary millisecond pulsars (P = 13 and 33 ms), as well as the slowest-spinning radio pulsar currently known (P = 23.5 s). The survey has thus far detected 311 known pulsars, with spin periods ranging from 4 ms to 5.0 s and dispersion measures from 3.0 to 217 pc cm −3 . Known pulsars are detected at flux densities consistent with literature values. We find that the LOTAAS pulsar discoveries have, on average, longer spin periods than the known pulsar population. This may reflect different selection biases between LOTAAS and previous surveys, though it is also possible that slower-spinning pulsars preferentially have steeper radio spectra. LOTAAS is the deepest all-sky pulsar survey using a digital aperture array; we discuss some of the lessons learned that can inform the approach for similar surveys using future radio telescopes such as the Square Kilometre Array.

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Scattering analysis of LOFAR pulsar observations

Cited by 82 publications

References 63 publications

Probing Pulsar Scattering between 120 and 280 MHz with the MWA

Probing Pulsar Scattering between 120 and 280 MHz with the MWA

A Fokker–Planck Framework for Studying the Diffusion of Radio Burst Waves in the Solar Corona

The LOFAR Tied-Array All-Sky Survey (LOTAAS): Survey overview and initial pulsar discoveries

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