  Systematic variations of average observational characteristics and
correlation properties between different parameters of gamma-ray bursts (GRBs)
with time from 1991 April to 1994 September are revealed. It is hard to explain
the observed long-term variability by variations of experimental conditions.
The variability of GRB properties with the time scale of months to years,
together with the similarity between GRBs, solar hard X-ray flares and
terrestrial gamma-ray flashes, may indicate an origin of GRBs, at least partly,
within the heliosphere. Large-voltage and high-temperature pinch plasma columns
produced by disruptive electrical discharges in the outer heliosphere can
generate hard X-ray and gamma-ray flashes with energy spectra and spectral
evolution characters consistent with that observed in GRBs.
