Hercules X- 1 has been observed in the extreme ultra-violet (EUV), during a short "on" state, using the wide field camera (WFC) on the ROSAT mission. Emission spanning two separate orbital periods of this source is clearly visible, allowing the time of the eclipse to be established as 2448 113.1±0.4 Julian day (JD), in agreement with the predicted value of 2448 113.1605±0.0084 JD. The shape of the orbital light curve is consistent with existing models of the source. A search for emission from the pulsar during the "on" time has yielded no positive result. Measurement of the fluxes through two different filters puts the hydrogen column density to the source in the range 2 1019 to 2 1020. If, as deduced by McCray et al. (1982), the primary spectrum is that of a black body with kT about 0.1 keV, then a hydrogen column density in the range 1.2 1020 < NH < 2.0 1020 cm-2 is consistent with all available data.
Astronomy and Astrophysics
- Pub Date:
- March 1994
- stars: individual: Her X-1 - binaries: eclipsing - X-ray: stars