EUVE observations of Hercules X-1 during a short high-state turn-on

Observations of Hercules X-l by the Extreme Ultraviolet Explorer (EUVE) cov ering low state and the early part of the short high state are reported her e. This is the first EUV observation of this part of the 35 day cycle of He r X-l. The low-state portion of the EUV light curve (prior to the start of the short high state) has similar properties as that following the end of t he short high state : This is evidence that the low-state EW emission is pr imarily due to EUV reflection from the companion star HZ Her. The EUV light curve during the short high state is pulsed and closely resembles the aver age 2-12 keV X-ray short high-state light curve, indicating that the EUV em ission, like the X-ray emission, originates near the neutron star. The shor t high-state EUV spectrum is consistent with a blackbody of temperature sim ilar or equal to0.13 keV and radius similar or equal to 230 km, The short h igh-state EUV spectrum and pulse shape are similar to that in the soft X-ra ys (0.1-1 keV). The most likely origin of the EUV emission is reprocessed X -rays from the inner edge of the accretion disk, and the radius of the inne r edge of the accretion disk is likely to be small, consistent with that de termined from analysis of the X-ray pulse shape evolution.