Optical observational biases in the GRB redshift
  The measured redshifts of gamma-ray bursts (GRBs), which were first detected
by the Swift satellite, seem to be bigger on average than the redshifts of GRBs
detected by other satellites. We analyzed the redshift distribution of GRBs
triggered and observed by different satellites (Swift, HETE2, BeppoSax,
Ulyssses). After considering the possible biases {significant difference was
found at the p=95.70% level in the redshift distributions of GRBs measured by
HETE and the Swift.
