  We have recently studied LS 5039, a gamma-ray binary, with Giant Meterwave
Radio Telescope (GMRT) during its periastron and apastron passage. The results
presented here show that the spectra are inverted at the low frequency and the
flux densities do not differ significantly for two different orbital phases.
Assuming that the free-free absorption of radio in stellar wind environment is
responsible for the optically thick radio emission we calculated the free-free
absorption optical depth and constrained the height of the radio emitting
region from the orbital plane. The height is found to be around 1.6 AU for a
spherical stellar wind geometry. This estimate may change if the stellar wind
is focussed or the radio absorption is due to synchrotron self-absorption.

High Energy Astrophysical Phenomena