Spectral signature of atmospheric reflection in Hercules X-1/HZ Hercules during low and short high states
Abstract
We analyse RXTE/PCA X-ray spectra of the binary X-ray pulsar Her X-1/HZ Her during short high state and one binary orbit in the preceding low state, just before short high turn-on. The spectrum is well described by two continuum components (absorbed and unabsorbed). The resulting spectral parameters are modulated with orbital phase. During low state, a significant component of the flux, and its spectrum, is consistent with X-ray reflection off the face of the companion star HZ Her. This component has a significantly harder X-ray spectrum than the rest of the flux from the Her X-1 system. A second component in low state is consistent with emission from the accretion disc corona. During short high, a third strong component is present with a softer spectrum, which is associated with the neutron star and accretion disc. Due to this direct emission from the neutron star and accretion disc, the reflected emission is less clear; however, parameters and fluxes modulations during short high state indicate its presence. In low state, the hard X-ray flux (hν > 10 keV) peaks at orbital phase φorb ≃ 0.55, which is expected from a simple model of atmospheric reflection from the companion star. The offset indicates an asymmetry in the X-ray illumination of the companion, which could be due to shadowing of the the inner face of HZ Her by the accretion disc and/or stream.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2015
- DOI:
- 10.1093/mnras/stv1886
- arXiv:
- arXiv:1508.03357
- Bibcode:
- 2015MNRAS.453.4222A
- Keywords:
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- stars: individual: HZ Her;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- doi:10.1093/mnras/stv1886