Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-11-25
Astronomy and Astrophysics
Astrophysics
6 pages, 5 figures, accepted for publication by A&A
Scientific paper
10.1051/0004-6361:200810743
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 feed-back 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, of the Anomalous Lows and of the pulse period evolution, with a 5 yr quasi-periodicity, as evidence for strong physical interaction and feed-back between the major components in the system. We speculate that the 5 yr (10 yr) period is either due to a corresponding activity cycle of HZ Her or a natural ringing period of the physical system of coupled components. The question whether free precession really exists in neutron stars is of great importance for the understanding of matter with supra-nuclear density.
Klochkov Dmitry
Postnov Konstantin
Rothschild Richard E.
Shakura Nikolai
Staubert Rüdiger
No associations
LandOfFree
Two ~35 day clocks in Her X-1: evidence for neutron star free precession does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Two ~35 day clocks in Her X-1: evidence for neutron star free precession, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two ~35 day clocks in Her X-1: evidence for neutron star free precession will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-304243