Variable pulse profiles of Hercules X-1 repeating with the same irregular 35 d clock as the turn-ons
Staubert R, Klochkov D, Vasco D, Postnov K, Shakura N, Wilms J, Rothschild RE (2013)
Publication Status: Published
Publication Type: Journal article
Publication year: 2013
Journal
Publisher: EDP SCIENCES S A
Book Volume: 550
Article Number: ARTN A110
DOI: 10.1051/0004-6361/201220316
Abstract
The accreting X-ray pulsar Her X-1 shows two types of long-term variations, both with periods of similar to 35 days: 1) turn-on cycles, a modulation of the flux, with a ten-day long main-on and a five-day long short-on, separated by two off-states, and 2) a systematic variation in the shape of the 1.24 s pulse profile. While there is general consensus that the flux modulation is due to variable shading of the X-ray emitting regions on the surface of the neutron star by the precessing accretion disk, the physical reason for the variation in the pulse profiles has remained controversial. Following the suggestion that free precession of the neutron star may be responsible for the variation in the pulse profiles, we developed a physical model of strong feedback interaction between the neutron star and the accretion disk in order to explain the seemingly identical values for the periods of the two types of variations, which were found to be in basic synchronization. In a deep analysis of pulse profiles observed by several different satellites over the last three decades we now find that the clock behind the pulse profile variations shows exactly the same erratic behavior as the turn-on clock, even on short time scales (a few 35 d cycles), suggesting that there may in fact be only one 35 d clock in the system. If this is true, it raises serious questions with respect to the idea of free precession of the neutron star, namely how the neutron star can change its precessional period every few years by up to 2.5% and how the feedback can be so strong, such that these changes can be transmitted to the accretion disk on rather short time scales.
Authors with CRIS profile
Involved external institutions
Eberhard Karls Universität Tübingen
Germany (DE)
Sternberg Astronomical Institute
Russian Federation (RU)
University of California, San Diego
United States (USA) (US)
Germany (DE)
Sternberg Astronomical Institute
Russian Federation (RU)
University of California, San Diego
United States (USA) (US)
How to cite
APA:
Staubert, R., Klochkov, D., Vasco, D., Postnov, K., Shakura, N., Wilms, J., & Rothschild, R.E. (2013). Variable pulse profiles of Hercules X-1 repeating with the same irregular 35 d clock as the turn-ons. Astronomy & Astrophysics, 550. https://doi.org/10.1051/0004-6361/201220316
MLA:
Staubert, R., et al. "Variable pulse profiles of Hercules X-1 repeating with the same irregular 35 d clock as the turn-ons." Astronomy & Astrophysics 550 (2013).
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