HI gas in rejuvenated radio galaxies: GMRT observations of the DDRG   J1247+6723
  We report the detection of HI absorption towards the inner double of the double-double radio galaxy (DDRG) J1247+6723 with the Giant Metrewave Radio Telescope (GMRT). The inner double is a Giga-hertz peaked spectrum (GPS) source with a linear size of 14 pc while the overall size defined by the outer double is 1195 kpc, making it a giant radio source. The absorption profile is well resolved and consists of a number of components on either side of the optical systemic velocity. The neutral hydrogen column density is estimated to be N(HI)=6.73*10^{20}(T_s/100)(f_c/1.0) cm^{-2}, where T_s and f_c are the spin temperature and covering factor of the background source respectively. We explore any correlation between the occurrence of HI absorption and rejuvenation of radio activity and suggest that there could be a strong relationship between them. 
D.J. Saikia, Neeraj Gupta, C. Konar (NCRA-TIFR)