Resonances as a Diagnostic Tool from the Earth's Ionosphere/Magnetosphere to Neutron Stars and Black Holes
Dr. Vladimir A. Osherovich
EITI, NASA Goddard Space Flight Center
Sounder-stimulated plasma resonances and natural narrow-band emissions have been observed for decades by spacecraft in the Earth's ionosphere and magnetospheres of the Earth and other planets (like Jupiter). Particularly useful in plasma physics is the concept of the upper-hybrid frequency fuh^2= fpe^2 + fce^2, where fpe is the electron plasma frequency and fce is the electron gyro-frequency. Using fuh and the observed harmonics of fce or magnetometer data, one can infer the electron density which is difficult to measure directly in magnetospheric plasmas. The level of confidence of identification of fuh or fpe depends on the presence of other resonances in the spectra above fpe and below fpe. We show that the upper-hybrid frequency relation is also true for some resonances with frequencies below fpe. Such resonances, called diffuse resonances (Dn) in the ionosphere, happen to be a dominant feature in the URAP spectra collected in the Io torus during the close flyby by Ulysses. In the absence of fce harmonics Dn resonances were used to find the electron density and the magnetic field intensity which compared well with later calibrated magnetometer data. Most recently, Dn resonances have been identified in IMAGE/RPI sounder data. We will compare plasmagrams obtained by RPI during a quiet day with plasmagrams during a magnetic storm induced by a magnetic cloud on March 31, 2001. We use the change in the electron density and the magnetic field inferred from these plasmagrams to quantify the impact of the magnetic cloud on the magnetosphere.
Recently, the upper hybrid frequency concept was successfully applied to quasi-periodic oscillations (QPOs) in low-mass binary systems. Twin-peak kHz QPOs are observed in soft x-rays of 20 compact objects, presumably neutron star binaries. The Two Oscillator Model (TOM) interprets the lower kHz frequency as Keplerian and the higher one as the upper-hybrid frequency which depends on differential rotation of the star's magnetosphere. In this way TOM utilizes the well-known analogy between the Lorentz force in electro-dynamics and the Coriolis force in mechanics. We will illustrate this new model by spectra for the neutron-star binary Sco X-1 and the black-hole candidate GX 17+2 and compare TOM with other models.