ALEXIS Observations of the Diffuse Cosmic Background in the Extreme Ultraviolet

Abstract

Abstract.We present preliminary results of ALEXIS satellite observations of the extreme ultraviolet diffuse sky. ALEXIS was designed to be a half-sky monitor in three narrow wavelength bands between 13.0 and 19.0 nm. In our band centered at 172 Å we find a clear signal from the diffuse sky that is about 20 counts per second above the signal when looking at the dark earth from the same part of an orbit. This difference corresponds to an upper limit on the true cosmic diffuse background signal in this narrow band. When estimates of the geocoronal contributions, both in and out of band, are removed, our upper limit is reduced.