  Recently, magnetic reconnection during collisionless, stressed, X-point
collapse was studied using kinetic, 2.5D, fully electromagnetic, relativistic
Particle-in-Cell numerical code [D. Tsiklauri and T. Haruki, Phys. Plasmas, 14,
112905 (2007)]. Here we finalise the investigation of this topic by addressing
key outstanding physical questions. It has been established here that: (i)
reconnection out-of-plane electric field at the magnetic null is generated by
the electron pressure tensor off-diagonal terms, resembling to the case of
tearing unstable Harris current sheet studied by the GEM reconnection
challenge; (ii) For m_i / m_e >> 1 the time evolution of the reconnected flux
is independent of ion-electron mass ratio; also, in the case of m_i / m_e = 1
we show that reconnection proceeds slowly as the Hall term is zero; when m_i /
m_e >> 1 (i.e. the Hall term is non-zero) reconnection is fast and we
conjecture that this is due to magnetic field being frozen into electron fluid,
which moves significantly faster than ion fluid; (iii) within one Alfven time,
somewhat less than half (40%) of the initial total (roughly magnetic) energy is
converted into the kinetic energy of electrons, and somewhat more than half
(60%) into kinetic energy of ions (similar to solar flare observations); (iv)
in the strongly stressed X-point case, in about one Alfven time, a full
isotropy in all three spatial directions of the velocity distribution is seen
for super-thermal electrons (also commensurate to solar flare observations).

Astrophysics;Plasma Physics;Space Physics