Filaments in the southern giant lobe of Centaurus A: constraints on
  nature and origin from modelling and GMRT observations
  We present results from imaging of the radio filaments in the southern giant
lobe of Centaurus A using data from GMRT observations at 325 and 235 MHz, and
outcomes from filament modelling. The observations reveal a rich filamentary
structure, largely matching the morphology at 1.4 GHz. We find no clear
connection of the filaments to the jet. We seek to constrain the nature and
origin of the vertex and vortex filaments associated with the lobe and their
role in high-energy particle acceleration. We deduce that these filaments are
at most mildly overpressured with respect to the global lobe plasma showing no
evidence of large-scale efficient Fermi I-type particle acceleration, and
persist for ~ 2-3 Myr. We demonstrate that the dwarf galaxy KK 196 (AM
1318-444) cannot account for the features, and that surface plasma
instabilities, the internal sausage mode and radiative instabilities are highly
unlikely. An internal tearing instability and the kink mode are allowed within
the observational and growth time constraints and could develop in parallel on
different physical scales. We interpret the origin of the vertex and vortex
filaments in terms of weak shocks from transonic MHD turbulence or from a
moderately recent jet activity of the parent AGN, or an interplay of both.
