EUVE Broadband Detection of the Diffuse Sky Background

We present measurements of the diffuse EUV sky background in the two Deep Survey Telescope bandpass filters during first light observations of the Extreme Ultraviolet Explorer (EUVE)\@. We analyzed 40 minutes of data in the band centered at 100 Angstroms and 25 minutes of data centered at 200 Angstroms which were selected for especially low background. All nonastrophysical contributions to the data, e.g., particles, geocoronal photons and detector background, were investigated and accounted for appropriately. An astronomical flux was detected in the 100 Angstroms band and an upper limit to this flux was obtained in the 200 Angstroms band. If the sky spectrum is assumed to be flat or a power law continuum, then the detected sky background intensity in the 100 Angstroms band is comparable to previous measurements, while our upper limit in the 200 Angstroms band is the lowest measurement by at least a factor of 2.5\@. Assuming the source spectrum consists of line emission from a thin thermal plasma, the emission code of Landini-Fossi was used to limit the emission measure of the interstellar medium at temperatures from 10(5) to 10(7) K\@. These limits are compared to limits derived from B band, Be band and ROSAT S1 bandpass observations. It is found that no single temperature plasma can explain all the data. This work has been supported by NASA contracts NAS5-30180 and NAS5-29298.