Correlation between X‐Ray Light‐Curve Shape and Radio Arrival Time in the Vela Pulsar

Abstract

We report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania. We sought correlations between Vela's X-ray emission and radio arrival times on a pulse-by-pulse basis. At a confidence level of 99.8% we have found significantly higher flux density in Vela's main X-ray peak during radio pulses that arrived early. This excess flux shifts to the ''trough'' following the second X-ray peak during radio pulses that arrive later. Our results suggest that the mechanism producing the radio pulses is intimately connected to the mechanism producing X-rays. Current models using resonant absorption of radio emission in the outer magnetosphere as a cause of the X-ray emission are explored as a possible explanation for the correlation.

Towards explanation of the X-ray-radio correlation in the Vela pulsar

“…If the main pulse is less suppressed by the induced scattering to the precursor, it is more efficiently scattered to high energies. This is consistent with the observations: weaker radio pulses with less pronounced precursors are accompanied by the high‐energy pulses with stronger emission in the trough (Lommen et al 2007). Given that the variations of the scattering efficiencies are determined by the fluctuations of γ 0 , larger γ 0 imply less efficient induced scattering and simultaneously stronger high‐energy luminosities.…”

“…At the same time, smaller γ 0 imply more efficient induced scattering, a more pronounced radio precursor and stronger resultant radio pulses. All this is in line with the observed trends (Krishnamohan & Downs 1983; Lommen et al 2007). Thus, our model explains the salient features of the radio profile formation of the Vela pulsar, the peculiarities of its soft X‐ray profile as well as the observed X‐ray–radio connection.…”

“…In this case, the main pulse can more efficiently participate in the spontaneous scattering, and the resultant high‐energy component should be more pronounced. This is in line with the observed trend: in the Vela pulsar, weaker radio pulses are accompanied by stronger high‐energy emission at the position of peaks 3 and 4 (Lommen et al 2007). One can speculate that the fluctuations of the effective value of γ 0 make the dominant contribution to the variations of the efficiencies of the spontaneous and induced scatterings.…”

“…Resonant absorption of giant radio pulses should lead to a more pronounced momentum evolution of the particles and, correspondingly, to the larger synchrotron power emitted. At the same time, the intensity redistribution in the high-energy profile of the Vela pulsar and its dependence on the radio pulse intensity (Lommen et al 2007) still remains puzzling. This problem is addressed in the present paper.…”

Radio Pulsars

“…These fundamental observables show both deterministic and random properties, with random properties in particular showing variations over all timescales. At radio wavelengths, pulsar spectra are nearly power-law, but comparisons of pulse shape and structure among wavelength ranges yields great insight into emission geometry and processes (see, for example, Shearer et al 2003;Lommen et al 2007;Harding et al 2008;Strader et al 2013).…”