Wilms J (2007)
Publication Status: Published
Publication Type: Journal article
Publication year: 2007
Publisher: EDP SCIENCES S A
Book Volume: 465
Pages Range: L25-L28
Journal Issue: 2
DOI: 10.1051/0004-6361:20077098
Aims. We present the results of ten years of repeated measurements of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and report the discovery of a positive correlation of the centroid energy of this absorption feature in pulse phase averaged spectra with source luminosity.Methods. Our results are based on a uniform analysis of observations by the RXTE satellite from 1996 to 2005, using suffciently long observations of 12 individual 35-day Main-On states of the source.Results. The mean centroid energy E-c of the CRSF in pulse phase averaged spectra of Her X-1 during this time is around 40 keV, with significant variations from one Main-On state to the next. We find that the centroid energy of the CRSF in Her X-1 changes by similar to 5% in energy for a factor of 2 in luminosity. The correlation is positive, contrary to what is observed in some high luminosity transient pulsars.Conclusions. Our finding is the first significant measurement of a positive correlation between Ec and luminosity in any X-ray pulsar. We suggest that this behaviour is expected in the case of sub-Eddington accretion and present a calculation of a quantitative estimate, which is very consistent with the effect observed in Her X-1. We urge that Her X-1 is regularly monitored further and that other X-ray pulsars are investigated for a similar behaviour.
APA:
Wilms, J. (2007). Discovery of a flux-related change of the cyclotron line energy in Hercules X-1. Astronomy & Astrophysics, 465(2), L25-L28. https://dx.doi.org/10.1051/0004-6361:20077098
MLA:
Wilms, Jörn. "Discovery of a flux-related change of the cyclotron line energy in Hercules X-1." Astronomy & Astrophysics 465.2 (2007): L25-L28.
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