The EUV variability of the luminous QSO HS 1700+6416

We report on the first observations of variations in UV (intrinsic EUV 330 angstrom) flux of the luminous QSO HS 1700+6416 (z = 2.72) over a decade. The amplitude of variations increases from +/- 0.1 mag in the optical (R) to up to a factor of 3 at 1250 angstrom. This is apparently an extension of the increase in amplitude of variations towards shorter wavelengths observed with IUE in low z AGN (Paltani & Courvoisier 1996) to the EUV. The time-scale for variations with the largest amplitudes is 1/2 yr to years. We briefly discuss the consequences of the observed variations on the ionizing metagalactic UV background.