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XMM-Newton EPIC & OM Observations of Her X-1 over the 35 d Beat Period and an Anomalous Low State

2005; American Institute of Physics; Linguagem: Inglês

10.1063/1.2130274

1935-0465

Silvia Zane,

Astronomical Observations and Instrumentation

We present the results of a series of XMM‐Newton EPIC and OM observations of Her X‐1, spread over a wide range of the 35 d precession period. We confirm that the spin modulation of the neutron star is weak or absent in the low state — in marked contrast to the main or short‐on states. The strong fluorescence emission line at ∼ 6.4 keV is detected in all observations (apart from one taken in the middle of eclipse), with higher line energy, width and normalisation during the main‐on state. In addition, we report the detection of a second line near 7 keV in 10 of the 15 observations taken during the low‐intensity states of the system. We discuss these observations in the context of previous observations, investigate the origin of the soft and hard X‐rays and consider the emission site of the 6.4keV and 7keV emission lines.