  In the supersymmetric models with low scale supersymmetry (SUSY) breaking
where the gravitino mass is around keV, we show that the 3.5 keV $X-$ray lines
can be explained naturally through several different mechanisms: (I) A keV
scale dark gaugino plays the role of sterile neutrino in the presence of
bilinear $R-$partiy violation. Because the light dark gaugino obtains Majorana
mass only via gravity mediation, it is a decaying warm dark matter (DM)
candidate; (II) Compressed cold DM states, whose mass degeneracy is broken by
gavity mediated SUSY breaking, emit such a line via the heavier one decay into
the lighter one plus photon(s). A highly supersymmetric dark sector may readily
provide such kind of system; (III) Light axino, whose mass again is around the
gravitino mass, decays to neutrino plus gamma in the $R-$partiy violating SUSY.
Moreover, we comment on dark radiation from dark gaugino.
