2008/11/25 by R. Staubert, D. Klochkov, К. А. Постнов +5 · 34 citations
Earth and Planetary Sciences · Physics and Astronomy · #Accretion (finance) #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #High-pressure geophysics and materials #Intermediate polar #Neutron star #Physics #Precession #White dwarf #astro-ph
paper · pdf · doi:10.1051/0004-6361:200810743
published in Astronomy and Astrophysics 494(3), 1025-1030 (EDP Sciences) · 6 pages, 5 figures, accepted for publication by A&A
arxiv created 2008/11/25 · openalex publication_date 2008/12/22 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 <i>Turn-On<i/> cycles with two on- and two off-states and 2) in the changing <i>shape of the pulse profiles<i/> 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 <i>Anomalous Low<i/> (AL3), which Her X-1 experienced in 1999/2000, in the sense that there must have been one extra <i>Turn-On<i/> 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 “<i>Turn-On<i/> clock”) and free precession of the neutron star (the more stable “<i>Pulse profile<i/> 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 <i>Turn-On<i/> 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 <i>Turn-Ons<i/>, of the <i>Anomalous Lows<i/> 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 <i>activity cycle<i/> of HZ Her or a <i>natural ringing<i/> 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.