Localization of the Type III and Type II Radio Sources Using the Multiple Spacecraft Observations

G. Thejappa1, R. J. MacDowall2

1Department of Astronomy, University of Maryland, College Park MD 20742, USA
2NASA/GSFC, Greenbelt MD 20771, USA

We present a technique to determine the positions of type III and type II radio burst sources based on the difference in their arrival times at multiple spacecraft separated from each other by a wide range of angles and distances. The time of arrival differences at a pair of spacecraft locate the radio source on a hyperboloid of revolution with foci at the spacecraft. The time of arrival differences at three spacecraft place the radio source on the curve of intersection of two such hyperboloids. To fix the position at a point on this curve of intersection requires additional information. Some examples for such information are the surface of the sphere with radius corresponding to the fundamental or second harmonic of the electron plasma frequency (plasma emission mechanism is assumed), or observations from an another spacecraft providing additional signal time of arrival differences. The source locations found in this way at the intersections of hyperboloids and other surfaces can be called hyperboloic position fixes. The computation of these hyperboloic position fixes can be reduced to the solution of a quadratic or a quartic equation. However, in actual situations the low frequency signals experience delays as they propagate through the solar atmosphere. The refraction of the radio waves in the smoothly varying background plasma and the scattering by random density fluctuations are the two main propagation effects. Unless the measured arrival times at spacecraft are corrected for the propagation effects, the multi-spacecraft data can not be used to extract the positional information of the radio source. In this study, we also describe a method to compute the delays in the arrival times of the radio emissions at spacecraft located at different distances due to refraction and scattering by random density fluctuations using the Monte Carlo simulations.