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Re-assessment of the Accretion Disc Clock in Hercules X-1

Published online by Cambridge University Press:  05 December 2011

E. Jurua ,
M. Still ,
P. J. Meintjes ,
P. A. Charles  and
S. K Anguma
E. Jurua
Affiliation:
University of the Free State, P.O.Box 334, Bloemfontein 9300, South Africa Mbarara University of Science and Technology, P.O.Box 1410, Mbarara, Uganda
M. Still
Affiliation:
NASA Ames Research Center M/S 244-30, Moffett Field, CA 94035, USA
P. J. Meintjes
Affiliation:
University of the Free State, P.O.Box 334, Bloemfontein 9300, South Africa
P. A. Charles
Affiliation:
South African Astronomical Observatory, P.O. Box 9, Observatory 7935, South Africa, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa, and School of Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, JK
S. K Anguma
Affiliation:
University of the Free State, P.O.Box 334, Bloemfontein 9300, South Africa
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Abstract

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The Galactic neutron star X-ray binary Her X-1 shows a 35-day photometric modulation. Detected across a broad energy range, the modulation is prevalent in X-rays, cycling between low and high states. Since the discovery of the 35-day cycle of Her X-1, the X-ray source has entered and returned from an extended anomalous low state on at least seven occasions. Employing Rossi X-ray Timing Explorer All-Sky Monitor observations, prior predictions that Her X-1 would return from the 2003 - 2004 anomalous low state with a new precession period and accretion luminosity are verified. However, the precession has not been as coherent over recent years as predicted. Potentially there have been more minor anomalous low states between 2004 and the present day.

Keywords

accretion:accretion discs - binaries:eclipsing - star:individual (Hercules X-1) - stars:neutron
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S277: Tracing the Ancestry of Galaxies (on the land of our ancestors) , December 2010 , pp. 325 - 328
Copyright
Copyright © International Astronomical Union 2011

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