GRB 090426 is a short duration burst detected by Swift ( T _ { 90 } \sim 1.28 s in the observer frame , and T _ { 90 } \sim 0.33 s in the burst frame at z = 2.609 ) .
Its host galaxy properties and some \gamma -ray related correlations are analogous to those seen in long duration GRBs , which are believed to be of a massive-star origin ( so-called Type II GRBs ) .
We present the results of its early optical observations with the 0.8-m TNT telescope at Xinglong observatory , and the 1-m LOAO telescope at Mt .
Lemmon Optical Astronomy Observatory in Arizona .
Our well-sampled optical afterglow lightcurve covers from \sim 90 seconds to \sim 10 ^ { 4 } seconds post the GRB trigger .
It shows two shallow decay episodes that are likely due to energy injection , which end at \sim 230 seconds and \sim 7100 seconds , respectively .
The decay slopes post the injection phases are consistent with each other ( \alpha \simeq 1.22 ) .
The X-ray afterglow lightcurve appears to trace the optical , although the second energy injection phase was missed due to visibility constraints introduced by the Swift orbit .
The X-ray spectral index is \beta _ { X } \sim 1.0 without temporal evolution .
Its decay slope is consistent with the prediction of the forward shock model .
Both X-ray and optical emission is consistent with being in the same spectral regime above the cooling frequency ( \nu _ { c } ) .
The fact that \nu _ { c } is below the optical band from the very early epoch of the observation provides a constraint on the burst environment , which is similar to that seen in classical long duration GRBs .
We therefore suggest that death of a massive star is the possible progenitor of this short burst .