Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996umd..reptr....v&link_type=abstract
Technical Report, Maryland Univ. College Park, MD United States
Astronomy and Astrophysics
Astronomy
Extreme Ultraviolet Radiation, X Ray Binaries, Ultraviolet Astronomy, Emission Spectra, Extreme Ultraviolet Explorer Satellite, X Rays, Time Dependence, Sky Surveys (Astronomy), Spaceborne Astronomy, Black Body Radiation
Scientific paper
EUVE made possible for the first time observations of Her X-1 in the lower energy range of the strong soft component. Several X-ray pulsars show this component, but owing to the high galactic latitude and correspondingly low interstellar absorption towards Her X-1, it is the only X-ray binary system that EUVE is able to study. Since the emission in this band is likely to be due to reprocessed higher energy X-rays and since Her X-1 has strong, highly variable emission over many wavelengths, it was thought essential to complement the EUVE observations with simultaneous coverage in several wavebands. Five satellites and four ground-based observatories were used presenting a comprehensive view of emission from ionized material in several different environments ranging from the inner edge of the accretion disk to the magnetosphere and corona. The EUVE observations took place over four days during the main-on state of the 35-day cycle. The EUVE count rates (taken from the Deep Survey which has greater sensitivity than the spectrometer observations) showed a time dependence similar to that of the soft X-rays. The unusual low state of Her X-1 during our observations resulted in spectra of very low signal-to-noise ratio from the EUVE Short Wavelength Spectrometer. Continuum emission was detected but no line emission. A blackbody fixed at a temperature of 0.1 keV (the ROSAT value) provides a good fit. Because of the weak signal, small systematic errors in the background severely affect the continuum modelling. We have only recently completed a recalibration of the EUVE effective area function which is needed for a proper interpretation of the off-axis spectral data. This new calibration was obtained from examining the off-axis and on-axis spectra of HZ 43, a hot, nonvariable white dwarf, and is being prepared separately for publication. The results will be applied to a paper doing more sophisticated background and continuum modelling is currently underway.
Marshall Herman
Raymond John
Vrtilek Saeqa Dil
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