Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 0704.3572

The subpulse modulation properties of pulsars at 92 cm and the frequency dependence of subpulse modulation

P. Weltevrede·B. W. Stappers·R. T. Edwards
View original source ↗Read source document ↗Export metadata ↓

Abstract

A large sample of pulsars has been observed to study their subpulse modulation at an observing wavelength (when achievable) of both 21 and 92 cm using the Westerbork Synthesis Radio Telescope. In this paper we present the 92-cm data and a comparison is made with the already published 21-cm results. We analysed 191 pulsars at 92 cm using fluctuation spectra. The sample of pulsars is as unbiased as possible towards any particular pulsar characteristics. For 15 pulsars drifting subpulses are discovered for the first time and 26 of the new drifters found in the 21-cm data are confirmed. We discovered nulling for 8 sources and 8 pulsars are found to intermittently emit single pulses that have pulse energies similar to giant pulses. It is estimated that at least half of the total population of pulsars have drifting subpulses when observations with a high enough signal-to-noise ratio would be available. It could well be that the drifting subpulse mechanism is an intrinsic property of the emission mechanism itself, although for some pulsars it is difficult or impossible to detect. Drifting subpulses are in general found at both frequencies, although the chance of detecting drifting subpulses is possibly slightly higher at 92 cm. It appears that the youngest pulsars have the most disordered subpulses and the subpulses become more and more organized into drifting subpulses as the pulsar ages. The correlations with the modulation indices are argued to be consistent with the picture in which the radio emission can be divided in a drifting subpulse signal plus a quasi-steady signal which becomes, on average, stronger at high observing frequencies. The measured values of P3 at the two frequencies are highly correlated, but there is no evidence for a correlation with other pulsar parameters.

Explore related subjects

astro-ph

Keep this discovery

BibTeXRIS

P. Weltevrede, B. W. Stappers, R. T. Edwards. 2007-04-26. The subpulse modulation properties of pulsars at 92 cm and the frequency dependence of subpulse modulation. https://doi.org/10.1051/0004-6361:20066855

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2009

Cosmology from very high energy $γ$-rays

In this work we study how the cosmological parameter, the Hubble constant $H_0$, can be constrained by observation of very high energy (VHE) $γ$-rays at the TeV scale. The VHE $γ$-rays experience attenuation by background radiation field through $e^+e^-$ pair production during the propagation in the intergalactic space. This effect is proportional to the distance that the VHE $γ$-rays go through. Therefore the absorption of TeV $γ$-rays can be taken as cosmological distance indicator to constrain the cosmological parameters. Two blazars Mrk 501 and 1ES 1101-232, which have relatively good spectra measurements by the atmospheric Cerenkov telescope, are studied to constrain $H_0$. The mechanism constraining the Hubble constant adopted here is very different from the previous methods such as the observations of type Ia supernovae and the cosmic microwave background. However, at $2σ$ level, our result is consistent with other methods.

astro-ph↗
arXiv2009

Improved optical mass tracer for galaxy clusters calibrated using weak lensing measurements

We develop an improved mass tracer for clusters of galaxies from optically observed parameters, and calibrate the mass relation using weak gravitational lensing measurements. We employ a sample of ~ 13,000 optically-selected clusters from the Sloan Digital Sky Survey (SDSS) maxBCG catalog, with photometric redshifts in the range 0.1-0.3. The optical tracers we consider are cluster richness, cluster luminosity, luminosity of the brightest cluster galaxy (BCG), and combinations of these parameters. We measure the weak lensing signal around stacked clusters as a function of the various tracers, and use it to determine the tracer with the least amount of scatter. We further use the weak lensing data to calibrate the mass normalization. We find that the best mass estimator for massive clusters is a combination of cluster richness, N_{200}, and the luminosity of the brightest cluster galaxy, L_{BCG}: M_{200\barρ} = (1.27 +/- 0.08) (N_{200}/20)^{1.20 +/- 0.09} (L_{BCG}/\bar{L}_{BCG}(N_{200}))^{0.71 +/- 0.14} \times 10^{14} h^{-1} M_sun, where $\bar{L}_{BCG}(N_{200})$ is the observed mean BCG luminosity at a given richness. This improved mass tracer will enable the use of galaxy clusters as a more powerful tool for constraining cosmological parameters.

astro-ph↗
arXiv2009

Bayesian reconstruction of the cosmological large-scale structure: methodology, inverse algorithms and numerical optimization

We address the inverse problem of cosmic large-scale structure reconstruction from a Bayesian perspective. For a linear data model, a number of known and novel reconstruction schemes, which differ in terms of the underlying signal prior, data likelihood, and numerical inverse extra-regularization schemes are derived and classified. The Bayesian methodology presented in this paper tries to unify and extend the following methods: Wiener-filtering, Tikhonov regularization, Ridge regression, Maximum Entropy, and inverse regularization techniques. The inverse techniques considered here are the asymptotic regularization, the Jacobi, Steepest Descent, Newton-Raphson, Landweber-Fridman, and both linear and non-linear Krylov methods based on Fletcher-Reeves, Polak-Ribiere, and Hestenes-Stiefel Conjugate Gradients. The structures of the up-to-date highest-performing algorithms are presented, based on an operator scheme, which permits one to exploit the power of fast Fourier transforms. Using such an implementation of the generalized Wiener-filter in the novel ARGO-software package, the different numerical schemes are benchmarked with 1-, 2-, and 3-dimensional problems including structured white and Poissonian noise, data windowing and blurring effects. A novel numerical Krylov scheme is shown to be superior in terms of performance and fidelity. These fast inverse methods ultimately will enable the application of sampling techniques to explore complex joint posterior distributions. We outline how the space of the dark-matter density field, the peculiar velocity field, and the power spectrum can jointly be investigated by a Gibbs-sampling process. Such a method can be applied for the redshift distortions correction of the observed galaxies and for time-reversal reconstructions of the initial density field.

astro-ph↗