ASCA OBSERVATIONS OF THE IRON LINE STRUCTURE IN CYGNUS X-1

摘要

The black hole candidate Cyg X-1 was observed with the ASCA satellite on multiple occasions in 1993 and 1994 for a total exposure of about 7 days. The energy resolution of the ASCA SIS (ΔE/E ≈ 2% at 6 keV) allows the spectral structure in the iron K band to be studied in greater detail than before. We detected an iron emission line at 6.4 keV in almost all the data with an intrinsic line width of approx < 0.2 keV (1 σ) and an equivalent width of 10-30 eV. The line parameters show no clear orbital phase dependence. A broad edge feature was observed at E approx > 7 keV in all the spectra. Both the narrow iron emission-line and broad edge features are consistent with disk reflection from the outer parts of an ionized accretion disk where the most populous iron ion species is Fe XI.