The afterglow of GRB 090426 (thick blue line) in comparison with the afterglows of type II (thing gray lines) and type I (red symbols and lines; squares connected by splines are detections, downward triangles connected by thin dashed lines are upper limits) GRBs from the sample of Kann et al. (2011, 2010). These afterglows have been corrected for Galactic extinction, and the host galaxy contribution has been subtracted where possible (also in the case of GRB 090426). The afterglow of GRB 090426 is seen to be among the faint type II GRB afterglows, but it is brighter than most type I GRB afterglows or limits thereon.

The afterglow of GRB 090426 after it has been shifted to the z = 1 system, again in comparison with the samples (shifted using the same method) of Kann et al. (2011, 2010). The labelling is identical to that in Fig. A.1. It can now clearly be seen that the afterglow of GRB 090426 is readily comparable to the afterglow of type II GRBs (collapsar events), while it is much brighter than any type I GRB afterglow (merging compact objects), with the exception of GRB 060121, which is a controversial case.

X-ray to optical spectral energy distribution of the afterglow of GRB 090426 at t = 8 ks after the burst, calculated based on the fitted light curve (Fig. 4). The fit uses   ×  10²² cm^-2 and corresponds to a negligible host extinction, a gas column density of   ×  10²² cm^-2, and a spectral slope of β_OX = 0.90  ±  0.03 (χ² = 10.85 with 7 d.o.f., χ_ν = 1.55).