  In collision-poor plasmas from space, e.g., solar wind, terrestrial
magnetospheres, kinetic instabilities are expected to play a major role in
constraining the temperature anisotropy of plasma particles, but a definitive
answer can be given only after ascertaining their properties in these
environments. Present study describes the full spectrum of electron firehose
instabilities in the presence of suprathermal electron populations which are
ubiquitous in space plasmas. Suprathermal electrons stimulate both the periodic
and aperiodic branches, remarkable being the effects shown by the aperiodic
mode propagating obliquely to the ambient magnetic field which markedly exceeds
the growth rates of the parallel (periodic) branch reported recently in Lazar
et al., (2017a, MNRAS 464, 564). Derived exclusively in terms of the plasma
parameters, the anisotropy thresholds of this instability are also lowered in
the presence of suprathermal electrons, predicting an enhanced effectiveness in
the solar wind conditions. These results may also be relevant in various other
astrophysical contexts where the firehose instabilities involve, e.g., solar
flares, sites of magnetic field reconnection, accretion flows or plasma jets
leading to shocks and co-rotating interactions in heliosphere, interstellar
medium and galaxy clusters.
