The prospects of observing a pulsed neutron flux at very high energies from pulsars are discussed. Most likely candidates are the Vela pulsar at 2 × 1016 eV and the Crab Pulsar at 1017 eV.

The magnetic field and the relativistic electrons in the Crab Nebula cannot have originated at the time of the supernova explosion. The energy density in the magnetic field is so large that it must have been generated using the energy supply in the pulsar. The energies of the electrons are so high, and their lifetimes correspondingly are so short, that they must have been accelerated, again using the pulsar energy. The efficiency of these processes must be high, but there is an adequate energy supply.

Dr. Ostriker suggested that the main features of the Crab Nebula, in particular the value of its magnetic field and the energy of the particles, could be derived very simply and directly from the known characteristics of the pulsar. The link was through the radiation from a spinning dipole. The following summary was prepared by the Editors.

The Crab Nebula pulsar conforms to the model of a rotating magnetised neutron star in the rate of energy generation and the exponent of the rotation law.

It is suggested that the main pulse is due to electrons and the precursor to protons. Both must radiate in coherent bunches. Optical and X-ray radiation is by the synchrotron process.

The wisps observed in the Nebula may represent the release of an instability storing about 1043 erg and 1047–48 particles.

Finally, some considerations are made about the general relation between supernova remnants and rotating neutron stars.

The continuum emission from the Crab Nebula may be radiation from relativistic electrons moving in the electromagnetic wave field radiated by the rotating magnetic dipole of the pulsar. This radiation, called Synchro-Compton radiation, would show ordering over the whole nebula, as is observed in measurements of polarisation. The properties of this radiation are described in an Appendix.

In this paper we present an account of a theory of pulsar radio emission. The emission mechanism is via a maser amplification process. This theory avoids the difficulty of coherent plasma emission, that the bandwidth of radiation must be less than 1/2 λ. The high brightness radio temperature and the insensitivity of pulsar radio flux to pulsar periods can be easily accounted for.

The properties of the radio pulses from pulsars are described. The formation of pulses seems to be a geometric phenomenon, for which the beaming due to relativistic motion of the source is the only candidate at present. Values of the volume emissivity and surface flux density indicate that all the particles near the source must have relativistic energies.

Dr. Radhakrishnan outlined a geometrical theory of a rotating pattern of field lines, which would account for the pattern of polarisation observed in the integrated radio pulses from pulsars.

The radio pulses from pulsars are considered to be formed from the beamed radiation from relativistic electrons. This radiation is in low order harmonics of the gyro frequency, giving pulse shapes and polarisations which agree with observation.

A possible connection between the shapes of radio pulses and the emission of optical pulses, via the electron energy, leads to a suggested means of searching for visible pulsars with improved sensitivity.

We suggest that an oscillating interface, carrying a steady current between a rotating, radiating, magnetic dipole and an external plasma is the source of pulsar radiation produced over a broad band of high frequencies (108–1018 Hz). The efficiency of the radiation mechanism is so high that the oscillation energy goes mainly into radiation in each cycle of the oscillation.

It is usually considered that the beaming of the radiation coming out of a pulsar has to be strictly connected with the mechanism producing the radiation itself. We want to show that even when the emitting mechanism gives rise to an isotropically distributed radiation, the presence of a strong magnetic field will automatically beam the radiation preferentially along the magnetic field line rather than in any other direction. We have computed the Compton scattering and from that the opacity KH (K0 is the opacity for zero field). In Figure 1 the ratio KH/K0 is given vs. θ, the angle between the propagation vector and the magnetic field axis. Hq is a critical magnetic field numerically equal to 4.41 × 1013 G; Ne is the electron density. For the ordinary wave the opacity is reduced at θ = 0, while it is unaffected at θ = π/2 where KH → K0. Even at θ = π/4 the ratio KH/K0 is still ≃ 10−2, and a good beaming is still present. The values of the parameters are proper for a neutron star surface. It is to be noticed that the ratio KH/K0 is of the order of (ω/ωH)2 or [(kT/mc2)/(H/Hq]2. One therefore can conclude that the presence of a magnetic field itself assures the beaming of radiation along the field lines.

We point out the existence of a natural low-frequency cutoff in the spectrum of a synchrotron source. The turnover frequency is eB/mc 〈sin Ψ〉, where Ψ is the pitch angle for the electron motion. The spectrum below the turnover goes as vn, where n is the index in the electron energy distribution. For the Crab pulsar, a model with B ~ 106–107G and 〈sin Ψ〉 ~ 10-3–10-2 provides a plausible explanation for the turnover observed in the infrared.

We propose nonthermal plasma mechanisms to account for the most evident physical characteristics of pulsar emission, including the production of X- and γ-rays and the acceleration of high-energy particles. Special reference to the Crab Nebula pulsar (NP 0532) is made and an application of the same model to other non-thermal X-ray sources is suggested.