The frequency dependence of scattering imprints on pulsar observations

Geyer, M.; Karastergiou, A.

doi:10.1093/mnras/stw1724

Cited by 29 publications

(28 citation statements)

References 51 publications

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“…A turnover in the flux spectrum (unrelated to a long scattering tail) is seen for PSR J1935+1616. However, as shown in Geyer & Karastergiou (2016), such a scenario would involve an observable change in the pulse profile shapes at low frequencies, which is not evident in the data. Soft edges of the screen, multiple screens and low S/N profiles can render these particular effects difficult to discern.…”

Section: Psr J0040+5716mentioning

confidence: 77%

Scattering analysis of LOFAR pulsar observations

Geyer

Karastergiou

Kondratiev

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We measure the effects of interstellar scattering on average pulse profiles from 13 radio pulsars with simple pulse shapes. We use data from the LOFAR High Band Antennas, at frequencies between 110 and 190 MHz. We apply a forward fitting technique, and simultaneously determine the intrinsic pulse shape, assuming single Gaussian component profiles. We find that the constant τ , associated with scattering by a single thin screen, has a power-law dependence on frequency τ ∝ ν −α , with indices ranging from α = 1.50 to 4.0, despite simplest theoretical models predicting α = 4.0 or 4.4. Modelling the screen as an isotropic or extremely anisotropic scatterer, we find anisotropic scattering fits lead to larger power-law indices, often in better agreement with theoretically expected values. We compare the scattering models based on the inferred, frequency dependent parameters of the intrinsic pulse, and the resulting correction to the dispersion measure (DM). We highlight the cases in which fits of extreme anisotropic scattering are appealing, while stressing that the data do not strictly favour either model for any of the 13 pulsars. The pulsars show anomalous scattering properties that are consistent with finite scattering screens and/or anisotropy, but these data alone do not provide the means for an unambiguous characterization of the screens. We revisit the empirical τ versus DM relation and consider how our results support a frequency dependence of α. Very long baseline interferometry, and observations of the scattering and scintillation properties of these sources at higher frequencies, will provide further evidence.

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Section: Psr J0040+5716mentioning

confidence: 77%

Scattering analysis of LOFAR pulsar observations

Geyer

Karastergiou

Kondratiev

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…As we mentioned in the Introduction, and also discussed previously in Kijak et al (2011b) and Dembska et al (2015a) that may lead to severe underestimation of the received flux density, when measured by a standard pulse profile based method 2 . The theoretical aspects of the influence of interstellar scattering on the observed pulsar flux were also recently discussed by Geyer & Karastergiou (2016). This calls for caution when using archival (or catalog) flux density measurements, especially at low frequencies, where the effects of scattering-induced flux underestimation will be strongest.…”

Section: Resultsmentioning

confidence: 99%

Gigahertz-peaked Spectra Pulsars and Thermal Absorption Model

Kijak

Basu

Lewandowski

et al. 2017

ApJ

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We present the results of our radio interferometric observations of pulsars at 325 MHz and 610 MHz using the Giant Metrewave Radio Telescope (GMRT). We used the imaging method to estimate the flux densities of several pulsars at these radio frequencies. The analysis of the shapes of the pulsar spectra allowed us to identify five new gigahertz-peaked spectra (GPS) pulsars. Using the hypothesis that the spectral turnovers are caused by thermal free-free absorption in the interstellar medium, we modeled the spectra of all known objects of this kind. Using the model, we were able to put some observational constrains on the physical parameters of the absorbing matter, which allows us to distinguish between the possible sources of absorption. We also discuss the possible effects of the existence of GPS pulsars on future search surveys, showing that the optimal frequency range for finding such objects would be from a few GHz (for regular GPS sources) to possibly 10 GHz for pulsars and radio-magnetars exhibiting very strong absorption.

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“…They also see α values below 2.61 but discarded them due to poor data quality. Geyer & Karastergiou (2016) simulated anisotropicaly scattered data and fit it with the isotropic model which results in α values less than the theoretically predicted values as well as the effect of non-circular scattering screens leading to low α values (∼ 2.9). Scattering spectra with α < 4 have been interpreted as a limitation of assumptions underlying the thin scattering model.…”

Section: Introductionmentioning

confidence: 97%

Scattering Study of Pulsars below 100 MHz Using LWA1

Bansal

Taylor

Stovall

et al. 2019

ApJ

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Interstellar scattering causes pulsar profiles to grow asymmetrically, thus affecting the pulsar timing residuals, and is strongest at lower frequencies. Different Interstellar medium models predict different frequency (ν) and dispersion measure (DM) dependencies for the scattering time-scale τ sc . For Gaussian inhomogeneity the expected scaling relation is τ sc ∝ ν −4 DM 2 , while for a Kolmogorov distribution of irregularities, the expected relation is τ sc ∝ ν −4.4 DM 2.2 . Previous scattering studies show a wide range of scattering index across all ranges of DM. A scattering index below 4 is believed to be either due to limitations of the underlying assumptions of the thin screen model or an anisotropic scattering mechanism. We present a study of scattering for seven nearby pulsars (DM < 50 pc cm −3 ) observed at low frequencies (10 − 88 MHz), using the first station of the Long Wavelength Array (LWA1). We examine the scattering spectral index and DM variation over a period of about three years. The results yield insights into the small-scale structure of ISM as well as the applicability of the thin screen model for low DM pulsars.Assuming that the scattering occurs due to a thin screen between the observer and the source, the pulse broadening function can be expressed in terms of an exponential function ∼ exp(−t/τ sc ) with scattering parameter τ sc (Scheuer 1968). This is also known as the thin-screen model where different ISM models of electron density fluctuations predict different frequency dependencies for the scattering parameter given by τ sc ∝ ν −α , where α is the scattering time spectral index.

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The frequency dependence of scattering imprints on pulsar observations

Cited by 29 publications

References 51 publications

Scattering analysis of LOFAR pulsar observations

Scattering analysis of LOFAR pulsar observations

Gigahertz-peaked Spectra Pulsars and Thermal Absorption Model

Scattering Study of Pulsars below 100 MHz Using LWA1

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