GMRT 150 MHz follow up of diffuse steep spectrum radio emission in
  galaxy clusters
  It has been recently found that a few galaxy clusters host diffuse radio halo
emission with very steep synchrotron spectra ($\alpha$ > 1.6), which may be
classified as Ultra Steep Spectrum Radio Halos (USSRHs). USSRHs are expected in
the turbulence re-acceleration model for the origin of cluster radio halos, and
are best discovered and studied at low frequencies. We performed GMRT follow up
observations of three galaxy clusters at 150MHz, selected from the GMRT radio
halo survey, which are known to host an USSRH or candidate very steep spectrum
diffuse emission. This project is aimed to characterize the low frequency
spectrum of USSRHs for a detailed study of their origin and connection with
cluster mergers. We present preliminary results at 150 MHz of the cluster A697.
