Bruce W. Wardropper 1919-2004

Sieber, Harry

doi:10.1353/mln.2004.0102

Cited by 6 publications

(6 citation statements)

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“…The behaviour at the other frequencies is very similar. It is apparent that the modulation index decreases with increasing DM in each case, as shown earlier for a much smaller number of pulsars by Sieber (1982); Stinebring et al (2000). We fit a power law of the form:…”

Section: Results From the Data Driven Approachmentioning

confidence: 72%

“…RISS is responsible for weak long-term fluctuations in observed flux density when the effect of DISS is accounted for. It occurs because of focussing and defocussing of the pulsar emission by the scattering medium and has a timescale of days to months (Sieber 1982;Romani et al 1986;Rickett 1990;Bhat et al 1999). Experimentally Stinebring et al (2000) showed that high dispersion measure (DM) pulsars at large distances have nearly constant observed flux densities over years, indicating that the pulsar emission is stable when individual pulses are integrated for at least a few hours, and diffractive scintillation has been accounted for.…”

Section: Introductionmentioning

confidence: 99%

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Spectral properties of 441 radio pulsars

Jankowski

Straten

Keane

et al. 2017

Monthly Notices of the Royal Astronomical Society

199

185

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We present a study of the spectral properties of 441 pulsars observed with the Parkes radio telescope near the centre frequencies of 728, 1382 and 3100 MHz. The observations at 728 and 3100 MHz were conducted simultaneously using the dual-band 10-50cm receiver. These high-sensitivity, multi-frequency observations provide a systematic and uniform sample of pulsar flux densities. We combine our measurements with spectral data from the literature in order to derive the spectral properties of these pulsars. Using techniques from robust regression and information theory we classify the observed spectra in an objective, robust and unbiased way into five morphological classes: simple or broken power law, power law with either low or high-frequency cutoff and log-parabolic spectrum. While about 79% of the pulsars that could be classified have simple power law spectra, we find significant deviations in 73 pulsars, 35 of which have curved spectra, 25 with a spectral break and 10 with a low-frequency turn-over. We identify 11 gigahertz-peaked spectrum (GPS) pulsars, with 3 newly identified in this work and 8 confirmations of known GPS pulsars; 3 others show tentative evidence of GPS, but require further low-frequency measurements to support this classification. The weighted mean spectral index of all pulsars with simple power law spectra is −1.60 ± 0.03. The observed spectral indices are well described by a shifted log-normal distribution. The strongest correlations of spectral index are with spin-down luminosity, magnetic field at the light-cylinder and spin-down rate. We also investigate the physical origin of the observed spectral features and determine emission altitudes for three pulsars.

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Section: Results From the Data Driven Approachmentioning

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Spectral properties of 441 radio pulsars

Jankowski

Straten

Keane

et al. 2017

Monthly Notices of the Royal Astronomical Society

199

185

View full text Add to dashboard Cite

show abstract

“…In the early days of pulsar observations, slow fluctuations of pulsar amplitudes were reported by Cole, Hesse & Page (1970) and Huguenin, Taylor & Helfand (1973). But it was not recognized that they were an interstellar propagation effect until a close correlation between the time-scale of the intensity fluctuations and the pulsar dispersion measure was pointed out by Sieber (1982). Subsequently, Rickett, Coles & Bourgois (1984) explained these slow fluctuations as refractive interstellar scintillations (RISS).…”

Section: Introductionmentioning

confidence: 99%

Daily observations of interstellar scintillation in PSR B0329+54

Wang

Yan

Manchester

et al. 2008

Monthly Notices RAS

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Quasi‐continuous observations of PSR B03239+54 over 20 d using the Nanshan 25‐m telescope at 1540 MHz have been used to study the effects of refractive scintillation on the pulsar flux density and diffractive scintillation properties. Dynamic spectra were obtained from data sets of 90 min duration and diffractive parameters derived from a two‐dimensional auto‐correlation analysis. Secondary spectra were also computed but these showed no significant evidence for arc structure. Cross‐correlations between variations in the derived parameters were much lower than predicted by thin‐screen models and in one case was of opposite sign to the prediction. Observed modulation indices were larger than predicted by thin‐screen models with a Kolmogorov fluctuation spectrum. Structure functions were computed for the flux density, diffractive time‐scale and decorrelation bandwidth. These indicated a refractive time‐scale of 8 ± 2 h, much shorter than predicted by the thin‐screen model. The measured structure function slope of 0.4 ± 0.2 is also inconsistent with scattering by a single thin screen for which a slope of 2.0 is expected. All observations are consistent with scattering by an extended medium having a Kolmogorov fluctuation spectrum which is concentrated towards the pulsar. This interpretation is also consistent with recent observations of multiple diffuse scintillation arcs for this pulsar.

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“…The typical timescale of RISS is typically days to weeks, increasing with pulsar distance (Sieber 1982;Rickett et al 1984;Hancock et al 2019). With just one epoch of observation, even spanning many hours, we are unlikely to have observed during a period of strong RISS for any pulsar when compared to many observations spanning multiple epochs.…”

Section: Maximum Likelihood Jitter Resultsmentioning

confidence: 99%

Analysis of Multi-hour Continuous Observations of Seven Millisecond Pulsars

Shapiro-Albert

McLaughlin

Lam

et al. 2020

ApJ

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Precision pulsar timing can be used for a variety of astrophysical tests from the detection of gravitational waves to probing the properties of the interstellar medium (ISM). Here we present analyses of the noise contributions to pulsar timing residuals from continuous multi-hour observations of seven millisecond pulsars (MSPs). We present scintillation bandwidth measurements for all MSPs in the sample, some for the first time, and scintillation timescale measurements and lower limits for all MSPs for the first time. In addition, we present upper limits on the contribution of pulse phase jitter to the timing residual error for all MSPs. These long observations also allow us to constrain variations in dispersion measures (DMs) on hour-long timescales for several millisecond pulsars. We find that there are no apparent DM variations in any of the MSPs studied on these timescales as expected. In light of new radio telescopes such as the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which will be able to time many pulsars for a short time each day, we search for differences in timing precisions from continuous TOAs and from equivalent length time-discontinuous TOAs. We find no differences in the precision for any MSP in our sample, as expected. We conclude that the TOA variations are consistent with the expected breakdown into template-fitting, jitter, and scintillation errors.

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Bruce W. Wardropper 1919-2004

Cited by 6 publications

References 0 publications

Spectral properties of 441 radio pulsars

Spectral properties of 441 radio pulsars

Daily observations of interstellar scintillation in PSR B0329+54

Analysis of Multi-hour Continuous Observations of Seven Millisecond Pulsars

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