IMPROVING PULSAR DISTANCES BY MODELING INTERSTELLAR SCATTERING

We present here a method to study the distribution of electron density fluctuations in pulsar directions as well as to estimate pulsar dista nces. The method, based on a simple two-component model of the scatter ing medium discussed by Gwinn, Bartel & Cordes, uses scintillation and proper motion data in addition to the measurements of angular broaden ing and temporal broadening to solve for the model parameters, namely, the fractional distance to a discrete scatterer and the associated re lative scattering strength. We show how this method can be used to est imate pulsar distances reliably, when the location of a discrete scatt erer (e.g. an H II region), if any, is known. Considering the specific example of PSR B0736-40, we illustrate how a simple characterization of the Gum nebula region (using the data on the Vela pulsar) is possib le and can be used along with the temporal broadening measurements to estimate pulsar distances.