- Related item:
- Pulsar Astrophysics (IAU S337) The Next 50 Years Part of Proceedings of the International Astronomical Union Symposia and Colloquia
- Description:
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Ever since their discovery in 1967, pulsars and neutron stars have provided an unprecedented opportunity to study the extremes of physics. This started with the very rapid identification of pulsars as rotating neutron stars with extremely strong magnetic fields and, selecting just a few highlights from the following decades, was followed by the discovery of the Hulse–Taylor binary, millisecond pulsars, the first pulsars in globular clusters, the pulsar planets and the double pulsar. In the last decade alone, we have made some amazing discoveries and observations with an impact across all areas of astronomy. With these proceedings of IAU Symposium 337, the 50th anniversary of the discovery of pulsars is celebrated by reflecting on what we have learned from these remarkable physical laboratories and by casting our eyes forward to the exciting opportunities they will provide for physical and astrophysical studies in the coming decades.
- Related item:
- Scattering analysis of LOFAR pulsar observations
- Description:
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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.
- Related item:
- The frequency dependence of scattering imprints on pulsar observations
- Description:
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Observations of pulsars across the radio spectrum are revealing a dependence of the characteristic
scattering time (τ) on frequency, which is more complex than the simple power law
with a theoretically predicted power-law index. In this paper, we investigate these effects using
simulated pulsar data at frequencies below 300 MHz. We investigate different scattering mechanisms,
namely isotropic and anisotropic scattering, by thin screens along the line of sight,
and the particular frequency-dependent impact on pulsar profiles and scattering time-scales
of each. We also consider how the screen shape, location and offset along the line of sight
lead to specific observable effects. We evaluate how well forward fitting techniques perform in
determining τ . We investigate the systematic errors in τ associated with the use of an incorrect
fitting method and with the determination of an off-pulse baseline. Our simulations provide
examples of average pulse profiles at various frequencies. Using these, we compute spectra of
τ and mean flux for different scattering setups. We identify setups that lead to deviations from
the simple theoretical picture. This work provides a framework for interpretation of upcoming
low-frequency data, both in terms of modelling the interstellar medium and understanding
intrinsic emission properties of pulsars.
