arXiv subjects

J. Kuijpers

Publications and source records attributed to J. Kuijpers.

41 records · Page 3Linked to original sources

arXiv2005

Frequency dependence of the drifting subpulses of PSR B0031-07

The well known drifter PSR B0031-07 is known to exhibit drifting subpulses where the spacing between the drift bands (P_3) shows three distinct modes A, B and C corresponding to 12, 6 and 4 seconds respectively. We have investigated periodicities and polarisation properties of PSR B0031-07 for a sequence of 2700 single pulses taken simultaneously at 328 MHz and 4.85 GHz. We found that mode A occurs simultaneously at these frequencies, while modes B and C only occur at 328 MHz. However, when the pulsar is emitting in mode B at the lower frequency there is still emission at the higher frequency, hinting towards the presence of mode B emission at a weaker level. Further, we have established that modes A and B are associated with two orthogonal modes of polarisation, respectively. Based on these observations, we suggest a geometrical model where modes A and B at a given frequency are emitted in two concentric rings around the magnetic axis with mode B being nested inside mode A. Further, it is evident that this nested configuration is preserved across frequency with the higher frequency arising closer to the stellar surface compared to the lower one, consistent with the well known radius-to-frequency mapping operating in pulsars.

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arXiv2004

A Free-Electron Laser in the Pulsar Magnetosphere

We have studied systematically the free-electron laser in the context of high brightness pulsar radio emission. In this paper, we have numerically examined the case where a transverse electromagnetic wave is distorting the motion of a relativistic electron beam while travelling over one stellar radius ($ approx 10 :{km}$). For different sets of parameters, coherent emission is generated by bunches of beam electrons in the radio domain, with bandwidths of 3 GHz. Pulse power often reached $10^{13} :{W}$, which corresponds with brightness temperature of $10^{30} :{K}$. The duration of these pulses is of the order of nanoseconds. In the context of pulsar radio emission, our results indicate that the laser can produce elementary bursts of radiation which build up the observed microstructures of a few tens of microseconds duration. The process is sensitive mostly to the beam particles energy, number density and the background magnetic field, but much less so to the transverse wave parameters. We demonstrate that the operation of a free-electron laser with a transverse electromagnetic wiggler in the pulsar magnetosphere occurs preferably at moder ate Lorentz factors $ gamma geq 100$, high beam density $n gtrsim 0.1 n_{textrm{GJ}}(r_ ast)$ where $n_{textrm{GJ}}(r_ ast)$ is the Goldrei ch-Julian density at a stellar radius $r_ ast$, and finally, at large altitude where the background magnetic field is low $B_0 leq 10^{-2} textrm{T}$.

astro-ph↗

arXiv2003

LOFAR: A new radio telescope for low frequency radio observations: Science and project status

LOFAR, the Low Frequency Array, is a large radio telescope consisting about 100 soccer field sized antenna stations spread over a region of 400 km in diameter. It will operate in the frequency range from ~10 to 240 MHz, with a resolution at 240 MHz of better than an arcsecond. Its superb sensitivity will allow for a broad range of astrophysical studies. In this contribution we first discuss four major areas of astrophysical research in which LOFAR will undoubtedly make important contributions: reionisation, distant galaxies and AGNs, transient radio sources and cosmic rays. Subsequently, we will discuss the technical concept of the instrument and the status of the LOFAR project

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arXiv2003

On the Search for Coherent Radiation from Radio Pulsars

We have examined data from pulsars B0950+08 and B0329+54 for evidence of temporally coherent radiation using the modified coherence function (MCF) technique of Jenet et al. (2001). We consider the influence of both instrumental bandpass and interstellar propagation effects. Even after removal of the effects due to the instrumental bandpass, we detect a signature in the MCF of our PSR B0329+54 data which is consistent with the definition of a coherent signal. However, we model the effects due to interstellar scintillation for this pulsar and show that it reproduces the observed signature. In particular, the temporal coherence time is close to the reciprocal of the decorrelation bandwidth due to diffractive scintillation. Furthermore, comparison of the coherence times of three pulsars reported by Jenet et al. (2001) with their expected diffractive decorrelation bandwidths suggests that the detection of coherence in these pulsars is also likely a result of interstellar scintillation, and is not intrinsic to the pulsars.

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arXiv2001

Fast Magnetosonic Waves Driven by Gravitational Waves

The propagation of a gravitational wave (GW) through a magnetized plasma is considered. In particular, we study the excitation of fast magnetosonic waves (MSW) by a gravitational wave, using the linearized general-relativistic hydromagnetic equations. We derive the dispersion relation for the plasma, treating the gravitational wave as a perturbation in a Minkowski background space-time. We show that the presence of gravitational waves will drive magnetosonic waves in the plasma and discuss the potential astrophysical implications.

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