Electrons accelerated in relativistic collisionless shocks are usually assumed to follow a power-law energy distribution with an index of p .
Observationally , although most gamma-ray bursts ( GRBs ) have afterglows that are consistent with p > 2 , there are still a few GRBs suggestive of a hard ( p < 2 ) electron energy spectrum .
Our previous work showed that GRB 091127 gave strong evidence for a double power-law hard electron energy ( DPLH ) spectrum with 1 < p _ { 1 } < 2 , p _ { 2 } > 2 and an “ injection break ” assumed as \gamma _ { b } \propto \gamma ^ { q } in the highly relativistic regime , where \gamma is the bulk Lorentz factor of the jet .
In this paper , we show that GRB 060614 and GRB 060908 provide further evidence for such a DPLH spectrum .
We interpret the multi-band afterglow of GRB 060614 with the DPLH model in an homogeneous interstellar medium by taking into account a continuous energy injection process , while for GRB 060908 , a wind-like circumburst density profile is used .
The two bursts , along with GRB 091127 , suggest a similar behavior in the evolution of the injection break , with q \sim 0.5 .
Whether this represents a universal law of the injection break remains uncertain and more such afterglow observations are needed to test this conjecture .