Narrow iron K line and warm iron K edge in pulse phase spectra of Hercules X-1

Abstract

Spectra of the accreting neutron star Hercules X-1 observed with the EXOSAT GSPC detector on days 61,65,92 and 96 1984 were analysed for iron line features. A broad gaussian emission line with a FWHM of 1.32±0.13 keV was found during on, turn-off and short-on states in the 35-day-cycle at an energy of ~ 6.55keV in the pulse phase averaged spectra. In an observation on day 160 1984 a pulse phase dependent spectral analysis was performed. A warm Kα iron edge was introduced in the fit. A narrow line (FWHM ~ 0.4keV) and an edge (EK = 8.43±0.13keV) of warm iron FeXIX to FeXXII within the 99% confidence level were found. This is expected if the iron line flux originates in the magnetospause 1.8 108 cm distant from the neutron star. An electron temperature Te = 4.106K, an electron density ne = 7.3 1018 cm−3, a shell thickness δ = 1.2 105 cm and a source luminosity L ~ 1037 erg sec−1 (4.5 kpc) are in agreement with the observed iron line and soft X-ray flux.