GMRT observations of IC 711 -- The longest head-tail radio galaxy known
  We present low-frequency, GMRT observations at 240, 610 and 1300 MHz of
IC~711, a narrow angle tail (NAT) radio galaxy. The total angular extent of the
radio emission, $\sim 22$ arcmin, corresponds to a projected linear size of
$\sim 900$ kpc, making it the longest among the known head-tail radio galaxies.
The objectives of the GMRT observations were to investigate the radio
morphology, especially of the long tail structure, at low frequencies. The
radio structure, especially initial $\sim 10$ arcmin of tail being a long
straight feature, does not seem to be consistent with a simple circular motion
around the cluster centre, as previously suggested in the literature. Two sharp
bends after the straight section of the tail cast doubt on the prevailing idea
in the literature that the long narrow tails represent trails left behind by
the fast moving parent optical galaxy with respect to the cluster medium, as
the optical galaxy could not have undergone such sharp bends in its path, under
any conceivable gravitational influence of some individual galaxy or of the
overall cluster gravitational potential. In fact the tail does not seem to have
been influenced by the gravitational field of any of the cluster-member
galaxies. The radio spectrum of the head, coinciding with the optical galaxy,
is flat ($\alpha \stackrel{<}{_{\sim}}0.4$ for $S \propto \nu ^{-\alpha}$), but
steadily steepens along the radio tail, with the end part of the tail showing
the steepest spectrum ($\alpha \, {\sim}$ 4 -- 5) ever seen in any diffuse
radio emission region.
