  We apply relativistic equipartition synchrotron arguments to the radio data
of the tidal disruption event candidate Sw 1644+57. We find that, regardless of
the details of the equipartition scenario considered, the energy required to
produce the observed radio (i.e., energy in magnetic field and radio emitting
electrons) must increase by a factor of ~20 during the first 200 days. It then
saturates. This energy increase cannot be alleviated by a varying geometry of
the system. The radio data can be explained by: (i) An afterglow like emission
of the X-ray emitting narrow relativistic jet. The additional energy can arise
here from a slower moving material ejected in the first few days that gradually
catches up with the slowing down blast wave (Berger et al. 2012). However, this
requires at least ~4x10^{53} erg in the slower moving outflow. This is much
more than the energy of the fast moving outflow that produced the early X-rays
and it severely constrains the overall energy budget. (ii) Alternatively, the
radio may arise from a mildly relativistic quasi-spherical outflow. Here, the
energy for the radio emission increases with time to at least ~10^{51} erg
after 200 days. This scenario requires, however, a second X-ray emitting
collimated relativistic component. Given these results, it is worthwhile to
consider models in which the energy of the magnetic field and/or of the radio
emitting electrons increases with time without a continuous energy supply to
the blast wave. This can happen, for example, if the energy is injected
initially mostly in one form (Poynting flux or baryonic) and it is gradually
converted to the other form, leading to a deviation from equipartition. Another
intriguing possibility is that a gradually decreasing Inverse Compton cooling
modifies the synchrotron emission and leads to an increase of the available
energy in the radio emitting electrons (Kumar et al. 2013).
