Two ~35 day clocks in Hercules X-1: evidence for neutron star free precession
Rüdiger Staubert,D. Klochkov,Konstantin Postnov,N. I. Shakura,Jörn Wilms,Richard E. Rothschild +5 more
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In this article, the authors present evidence for the existence of two ∼35 day clocks in the Her X-1/HZ Her binary system, both with a period of about ∼35 days: the less stable Turn-On clock and the more stable Pulse profile clock.Abstract:
We present evidence for the existence of two ∼35 day clocks in the Her X-1/HZ Her binary system. ∼35 day modulations are observed 1) in the Turn-On cycles with two on- and two off-states and 2) in the changing shape of the pulse profiles which re-appears regularly. The two ways of counting the 35 day cycles are generally in synchronization. This synchronization did apparently break down temporarily during the long Anomalous Low (AL3), which Her X-1 experienced in 1999/2000, in the sense that there must have been one extra Turn-On cycle. Our working hypothesis is that there are two clocks in the system, both with a period of about ∼35 days: precession of the accretion disk (the less stable “Turn-On clock”) and free precession of the neutron star (the more stable “Pulse profile clock”). We suggest that free precession of the neutron star is the master clock and that the precession of the accretion disk is basically synchronized to that of the neutron star through a feedback mechanism in the binary system. However, the Turn-On clock can slip against its master when the accretion disk has a very low inclination, as is observed to be the case during AL3. We take the apparent correlation between the histories of the Turn-Ons ,o f theAnomalous Lows and of the pulse period evolution, with a 5 yr quasi-periodicity, as evidence for strong physical interaction and feedback between the major components in the system. We speculate that the 5 yr (10 yr) period is due either to a corresponding activity cycle of HZ Her or a natural ringing period of the physical system of coupled components. The question of whether free precession really exists in neutron stars is very important for understanding matter with supra-nuclear density.read more
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Cyclotron lines in highly magnetized neutron stars
Ruediger Staubert,Joachim Trümper,Eckhard Kendziorra,D. Klochkov,Konstantin Postnov,Peter Kretschmar,Katja Pottschmidt,Katja Pottschmidt,Frank Haberl,Richard E. Rothschild,Andrea Santangelo,Jörn Wilms,Ingo Kreykenbohm,Felix Fürst +13 more
TL;DR: In this article, an updated list of X-ray binary pulsars with magnetic fields on the order of several 1012 Gauss is presented, along with a discussion of the underlying physics of accretion onto highly magnetized neutron stars.
Journal ArticleDOI
Possible evidence for free precession of a strongly magnetized neutron star in the magnetar 4U 0142+61.
Kazuo Makishima,Teruaki Enoto,J. Hiraga,Toshio Nakano,Koji Nakazawa,Soki Sakurai,Masaki Sasano,Hiroshi Murakami +7 more
TL;DR: The magnetar 4 U 0142+61, one of the prototypes of this class, was studied in broadband x rays with the Suzaku observatory and suggests a strong toroidal magnetic field, ∼ 10(12) T, residing inside the object.
Journal ArticleDOI
Cyclotron lines in highly magnetized neutron stars
Ruediger Staubert,Joachim Trümper,Eckhard Kendziorra,D. Klochkov,Konstantin Postnov,Peter Kretschmar,Katja Pottschmidt,Katja Pottschmidt,Frank Haberl,Richard E. Rothschild,Andrea Santangelo,Jörn Wilms,Ingo Kreykenbohm,Felix Fürst +13 more
TL;DR: In this paper, the cyclotron resonant scattering features (CRSF) were used to measure the magnetic field strength of a binary pulsar with magnetic fields on the order of several 1012 Gauss.
Journal ArticleDOI
Updating the orbital ephemeris of Hercules X-1; rate of decay and eccentricity of the orbit
TL;DR: In this paper, an update of the orbital ephemeris of the binary X-ray pulsar Her X-1 and an improved value for the rate of orbital decay were reported.
Journal ArticleDOI
A new model for the X-ray continuum of the magnetized accreting pulsars
TL;DR: In this article, a detailed spectral study of the X-ray emission recorded from the high-mass Xray binary pulsars Cen X-3, 4U 0115+63, and Her X-1 is carried out by using Beppo SAX and NuStar data, together with an advanced version of the compmag model, which provides a physical description of the high energy emission from accreting pulsars, including the thermal and bulk Comptonization of cyclotron and bremsstrahlung seed photons along the neutron star accretion column.
References
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TL;DR: In this article, a new pulsating X-ray source with a 1.24-sec period in the constellation Hercules was discovered, which was interpreted as due to an occulting binary system, with the intensity changes due to occultation of the Xray source by its companion.
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D. Gerend,P.E. Boynton +1 more
TL;DR: In this article, a simple model based on a tilted, precessing accretion disk was proposed to simulate the 1d/sub./7 optical light curve of Her X-1/HZ Her.
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Further x-ray observations of Hercules X-1 from Uhuru
TL;DR: The 1.24-sec period is observed to decrease with time, with an overall change of 4.5 microsec between January and July 1972 as discussed by the authors, and the X-ray intensity shows regular on states lasting 11 or 12 days followed by 24-day off states.