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Abstract

We have studied the iron line intensity variation of Her X-1 over its characteristic periodicities such as the pulse period of 1.24 s, the orbital period of 1.7 days, and the long-term period of 35 days, with Ginga observations made from 1989 April to June. From an analysis of the pulse phase-resolved spectra obtained from the MAIN HIGH state of Her X-1, we discover that the line flux modulates from (4.3 +/- 1.9) x 10-3 to (1.0 +/- 0.3) x 10-2 photons/sq cm/s (the average 7.5 x 10-3/sq/cm/s) during the pulse period. We also find that the line flux modulation is consistent with that of soft X-rays below 1 keV observed by previous authors. From the study of the orbital phase and the 35 day cycle dependences, we see the following facts: (1) the line flux observed during the high intensity state of Her X-1 does not depend significantly on the orbital phase of 0.2-0.9, while the flux is almost invisible during the eclipse, (2) the pattern of the iron line flux modulation along the 35 day cycle is very similar to that of the continuum X-ray flux. With the line pulsations and the solid angle required to explain the equivalent width of the line in the MAIN HIGH state, we deduce that the extent of reprocessing site is less than 1010 cm. Based on the similarity of the modulation pattern between the line flux and the continuum flux along the 35 day cycle, and the equivalent width change, we suggest that the line flux variation is mainly due to occultation of the reprocessing site by an accretion disk rather than to a change of reprocessing site; some line flux, very small compared with the MAIN HIGH line flux, from an additional site may be responsible for the equivalent width change.

Iron line intensity variations of Hercules X-1 over the pulse phase and the 35 day cycle

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