Observational manifestations of the change in the tilt of the accretion disk to the orbital plane in her X-1/HZ her with phase of its 35-day period

Klochkov, D.; Шакура, Н. И.; Постнов, К. А.; Staubert, R.; Wilms, J.; Ketsaris, N. A.

doi:10.1134/s1063773706120024

Cited by 35 publications

(35 citation statements)

References 29 publications

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“…After that, a second, substantially lower maximum, the Short-On, emerges for a few days, after which a second minimum concludes the cycle (see Klochkov et al 2006). It is generally assumed that the modulation is due to shading by the precessing accretion disk (Gerend & Boynton 1976).…”

Section: Turn-on Cycle Countingmentioning

confidence: 99%

Two ~35 day clocks in Hercules X-1: evidence for neutron star free precession

Staubert¹,

Klochkov²,

Постнов³

et al. 2008

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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, of the Anomalous 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.

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Section: Turn-on Cycle Countingmentioning

confidence: 99%

Two ~35 day clocks in Hercules X-1: evidence for neutron star free precession

Staubert¹,

Klochkov²,

Постнов³

et al. 2008

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“…The periodicity is believed to be caused by the warped accretion disk precessing with a ∼35 d period (e.g., Klochkov et al 2006, and references therein). In most cases, only the data from mainons have sufficient quality for the analysis of the cyclotron line.…”

Section: Introductionmentioning

confidence: 99%

Swift/BAT measurements of the cyclotron line energy decay in the accreting neutron star Hercules X-1: indication of an evolution of the magnetic field?

Klochkov

Staubert

Постнов

et al. 2015

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Context. The magnetic field is a crucial ingredient of neutron stars. It governs the physics of accretion and of the resulting highenergy emission in accreting pulsars. Studies of the cyclotron resonant scattering features (CRSFs) seen as absorption lines in the X-ray spectra of the pulsars permit direct measurements of the field strength. Aims. From an analysis of a number of pointed observations with different instruments, the energy of CRSF, E cyc , has recently been found to decay in Her X-1 , which is one of the best-studied accreting pulsars. We present our analysis of a homogeneous and almost uninterrupted monitoring of the line energy with Swift/BAT. Methods. We analyzed the archival Swift/BAT observations of Her X-1 from 2005 to 2014. The data were used to measure the CRSF energy averaged over several months. Results. The analysis confirms the long-term decay of the line energy. The downward trend is highly significant and consistent with the trend measured with the pointed observations: dE cyc /dt ∼ −0.3 keV per year. Conclusions. The decay of E cyc either indicates a local evolution of the magnetic field structure in the polar regions of the neutron star or a geometrical displacement of the line-forming region due to long-term changes in the structure of the X-ray emitting region. The shortness of the observed timescale of the decay, −E cyc /Ė cyc ∼ 100 yr, suggests that trend reversals and/or jumps of the line energy might be observed in the future.

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“…Since the discovery of Her X-1 as an accreting binary X-ray pulsar by UHURU in 1972 (Tananbaum et al 1972), it has been known that the flux varies strongly on three different time scales (in addition to the 1.237 s pulsation): the ∼35 d on-off period, the 1.70 d binary eclipses (of ∼6 h duration) and the 1.62 d period with similarly long "dips". For details on these modulations and the underlying physics, see e.g., Klochkov et al (2006) and Staubert et al (2013). Figure A .1 (upper panel) shows the Her X-1 light curve of the Main-On of 35 d cycle 462, as measured (in orbital averages) by Swift/BAT.…”

Section: A1 Determination Of X-ray Fluxmentioning

confidence: 99%

Continued decay in the cyclotron line energy in Hercules X-1

Staubert

Klochkov

Vybornov

et al. 2016

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The centroid energy E cyc of the cyclotron line in the spectrum of the binary X-ray pulsar Her X-1 has been found to decrease with time on a time scale of a few tens of years -surprisingly short in astrophysical terms. This was found for the pulse phase-averaged line centroid energy using observational data from various X-ray satellites over the time period 1996 to 2012, establishing a reduction of ∼4 keV. Here we report on the result of a new observation by NuSTAR performed in August 2015. The earlier results are confirmed and strengthened with respect to both the dependence of E cyc on flux (it is still present after 2006) and the dependence on time: the long-term decay continued with the same rate, corresponding to a reduction of ∼5 keV in 20 yr.

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Observational manifestations of the change in the tilt of the accretion disk to the orbital plane in her X-1/HZ her with phase of its 35-day period

Cited by 35 publications

References 29 publications

Two ~35 day clocks in Hercules X-1: evidence for neutron star free precession

Two ~35 day clocks in Hercules X-1: evidence for neutron star free precession

Swift/BAT measurements of the cyclotron line energy decay in the accreting neutron star Hercules X-1: indication of an evolution of the magnetic field?

Continued decay in the cyclotron line energy in Hercules X-1

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