Low-frequency radio observations of Seyfert galaxies: A test to the
  unification scheme
  Aims. We present low-frequency radio imaging and spectral properties of a
well defined sample of Seyfert galaxies using GMRT 240/610 MHz dual frequency
observations. Radio spectra of Seyfert galaxies over 240 MHz to 5.0 GHz are
investigated using 240 MHz, 610 MHz flux densities derived from GMRT, and 1.4
GHz and 5.0 GHz flux densities mainly from published VLA data. We test the
predictions of Seyfert unification scheme by comparing the radio properties of
Seyfert type 1s and type 2s. Methods. We choose a sample such that the two
Seyfert subtypes have matched distributions in parameters that are independent
to the orientation of AGN, obscuring torus and the host galaxy. Our sample
selection criteria allow us to assume that the two Seyfert subtypes are
intrinsically similar within the framework of the unification scheme. Results.
The new observations at 240/610 MHz, together with archival observations at 1.4
GHz, 5.0 GHz show that type 1s and type 2s have statistically similar radio
luminosity distributions at 240 MHz, 610 MHz, 1.4 GHz and 5.0 GHz. The spectral
indices at selected frequency intervals as well as index measured over 240 MHz
to 5.0 GHz for the two Seyfert subtypes have similar distributions with median
spectral index $/sim$ -0.7, consistent with the synchrotron emission from
optically thin plasma. In our snap-shot 240/610 MHz GMRT observations, most of
the Seyfert galaxies show primarily an unresolved central radio component,
except a few sources in which faint kpc-scale extended emission is apparent at
610 MHz. Our results on the statistical comparison of the multifrequency radio
properties of our sample Seyfert galaxies are in agreement with the predictions
of the Seyfert unification scheme.
