Density of warm ionized gas near the Galactic Center: Low radio
  frequency observations
  We have observed the Galactic Center (GC) region at 0.154 and 0.255 GHz with
the GMRT. A total of 62 compact likely extragalactic sources are detected.
Their scattering sizes go down linearly with increasing angular distance from
the GC up to about 1 deg. The apparent scattering sizes of sources are more
than an order of magnitude down than predicted earlier by the NE2001 model of
Galactic electron distribution within 359.5 deg < l < 0.5 deg and -0.5 deg <b
<0.5 deg (Hyperstrong scattering region) of the Galaxy. High free-free optical
depths are observed towards most of the extended nonthermal sources within 0.6
deg from the GC. Significant variation of optical depth indicate the absorbing
medium is patchy at an angular scale of 10' and electron density is ~10 per cc
that matches with the NE2001 model. This model predicts the extragalactic (EG)
sources to be resolved out from 1.4 GHz interferometric surveys. However, 8
likely EG sources out of 10 expected in the region are present in 1.4 GHz
catalog. Ionized interfaces of dense molecular clouds to the ambient medium are
most likely responsible for strong scattering and low radio frequency
absorption. However, dense GC clouds traced by CS $J=1-0$ emission are found to
have a narrow distribution of ~0.2 deg across the Galactic plane. Angular
distribution of most of the EG sources seen through the so called Hyperstrong
scattering region are random in $b$, and typically ~7 out of 10 sources will
not be seen through to the dense molecular clouds, and it explains why most of
them are not scatter broadened at 1.4 GHz.
