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

Abstract

Recent observations of the Vela pulsar have revealed a peculiar connection of its emission in the soft X-ray and radio ranges. We suggest the model of the radio pulse formation in the Vela pulsar, develop the theory of the radio photon reprocessing to high energies, and on this basis interpret the observed X-ray-radio connection. The processes of spontaneous and induced scattering of radio waves off the spiralling particles and their observational consequences are examined. The particles are assumed to acquire relativistic gyration energies due to resonant absorption of the radio emission in the outer magnetosphere of a pulsar. The spectral and angular distributions of the spontaneously scattered power are analysed and compared with the characteristics of the particle synchrotron emission. The consequences of intensity transfer from the radio beam to the background in the course of induced scattering are studied as well. It is demonstrated that the induced scattering can account for the basic features of the Vela's radio profile and its pulse-to-pulse fluctuations. In particular, it can explain a greater role of the leading component and its earlier arrival in stronger pulses. The studies of the radio photon reprocessing to high energies in application to the Vela pulsar show that the scattered and synchrotron spectra peak at ∼0.8 and 0.2 keV, respectively, with the corresponding luminosities of 10 29 and 10 31 erg s -1 . The reprocessing inside the light cylinder results in the profile component, which stretches from the radio pulse position to ∼30° earlier in pulse phase. The synchrotron emission beyond the light cylinder presumably contributes to the component that lags the radio pulse by ∼90°. Within the framework of our model, the observed X-ray-radio connection is explained in terms of the interplay between the processes of induced and spontaneous scattering of the radio pulse.