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. 
G. Macario, T. Venturi, D. Dallacasa, S. Giacintucci, G. Brunetti, R.   Cassano, C. H. Ishwara-Chandra, R. Athreya
astro-ph.CO