Pulsar Research at New Mexico Tech

Pulsars are a unique laboratory for studying physics under extreme conditions which cannot be duplicated on earth. Their magnetospheres contain highly relativistic electron-positron plasmas which are confined and channeled by teragauss magnetic fields. The extremely high precision which which their rotation rate can be measured has provided a new, and successful, test of Einstein's theory of general relativity. However, despite nearly thirty years of study, in which a wealth of high-precision radio data has been gathered on these objects, we still do not understand the basic mechanism by which these dense stars radiate.

We have, therefore, undertaken a program to combine new radio data with new theoretical work to attempt to determine how pulsars shine. On the observational side, we are using new technologies to develop new radio instrumentation. When used with the VLA, or other telescopes such as Arecibo or Parkes, our experiments sample the signal from several bright pulsars at rates up to several tens of million samples per second. Thus, we can measure fluctuations in the emission at a time resolution down to a few nanoseconds. This allows us to detect structures as smaller than 1 m in the pulsar's atmosphere, and to follow their evolution in time. We believe these small structures are intimately connected to the still-unknown radio emission mechanism.

On the theoretical side, we are studying the basic physics of the region which emits the radio signal. This region is believed to contain a relativistic plamsa streaming out from the star in two ``lighthouse beams'', one located over each magnetic pole of the starr. This is the region where the high particle energies, high plasma densities and strong magnetic fields make the physics interestingly complex. These plasma streams are thought to be very unstable, and to break up into turbulent clumps on their way out of the magnetosphere. These clumps are probably the source of the radio emission; we believe they are the tiny structures we are resolving in time. We are applying theoretical techniques developed in the study of terrestrial, laboratory plasmas with numerical methods, in order to study the growth and development of this streaming plasma. Comparison of our theoretical predictions with the high time resolution data will allow us to specify the physical conditions, and the emission mechanism, from these stars.

--- Tim Hankins, Jean Eilek; with J. Kern (NMT/NRAO),
J. Weatherall (FAA), J. Rankin (Vermont), A. Jessner (MPIfR)