HEAO 1 observations of the long-term variability of Hercules X-1

Gorecki, A.; Levine, A. M.; Bautz, M. W.; Lang, F. L.; Primini, F. A.; Lewin, W. H. G.; Baity, W. A.; Gruber, D.; Rothschild, R. E.

doi:10.1086/159900

Cited by 13 publications

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“…It shows a 35 day period on-off cycle in which a main-on and a short-on are present. The flux from the source varies roughly a factor of three between the main-on and the short-on [6]. Low flux level emission was also detected between the two on of the 35 day cycle.…”

Section: Introductionmentioning

confidence: 86%

The pulsed light curves of Her X–1 as observed by BeppoSAX

Fiume¹,

Orlandini²,

Cusumano³

et al. 1997

AIP Conference Proceedings

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Abstract. We report on the timing analysis of the observation of the X-ray binary pulsar Her X-1 performed during the BeppoSAX Science Verification Phase. The observation covered more that two full orbital cycles near the maximum of the mainon in the 35 day cycle of Her X-1. We present the pulse profiles from 0.1 to 100 keV. Major changes are present below 1 keV, where the appearance of a broad peak is interpreted as re-processing from the inner part of the accretion disk, and above 10 keV, where the pulse profile is less structured and the main peak is appreciably harder. The hardness ratios show complex changes with pulse phase at different energies.

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Section: Introductionmentioning

confidence: 86%

The pulsed light curves of Her X–1 as observed by BeppoSAX

Fiume¹,

Orlandini²,

Cusumano³

et al. 1997

AIP Conference Proceedings

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“…Note that the best-studied cycles, in Her X-1 and SS433, deviate from perfect periodicity. Long-term cyclic behavior in Her X-1 (from Gorecki et al, 1982), LMC X-4 (from Lang et al, 1981), Cyg X-1 (from Priedhorsky et al, 1983), SMC X-1 (from Gruber and Rothschild, 1984), and Cen X-3 (from Priedhorsky and Terrell, 1983).…”

Section: Superorbital Cycles In Massive X-ray Binariesmentioning

confidence: 99%

Long-term cycles in cosmic X-ray sources

Priedhorsky

Holt

1987

Space Sci Rev

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Most of what we know about galactic X-ray binaries comes from their time variation, particularly periodic variations corresponding to neutron star rotation, and binary motion. Longer cycles or quasi-cycles are much harder to observe because of the shortage of instrumentation suitable for long-term monitoring. Nonetheless, cycle with periods up to a few years have been seen in several galactic binaries.Cycles of ~ 30-300 days have been confirmed for four high-mass systems, LMC X-4, Her X-l, SS433, and Cyg X-l, and are suspected in several others. These cycles are observed in both the X-ray and optical bands, and represent cyclic variations in both the inner and outer parts of the accretion disk. Some component of these systems is precessing, but we are not certain which. It could be a misaligned companion star; the outer rim of the accretion disk, driven by radiative feedback; or the neutron star.Several low-mass X-ray binaries have quasi-periodic cycles, with periods ranging from 89 to 2 years. The amplitude of modulation ranges between ~ 50 and 100 ~o, i.e., both 'persistent' and 'transient' objects fall into this class. This activity is reminiscent of the superoutburst cycles of the SU UMa cataclysmic variables, and may be caused by similar mass-transfer instabilities.Periodic outbursts in the Be/neutron star systems seem to result from variable mass transfer in a wide, eccentric orbit. The relationship between the orbital cycle and the flux outbursts, however, is not well understood, and even the equivalence of the outburst and binary cycles remains hypothetical for most objects. Most likely, the periodic outbursts result from enhanced mass transfer at periastron.Compared to other aspects of X-ray astronomy, long-term activity has been much less intensively studied by both observers and theoreticians. A simple all-sky monitor in permanent operation could provide for the X-ray sky the same kind of data base provided to optical observers by the Harvard plates.

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“…In X-rays, the 35d cycle is characterized by a rapid turn-on, a "main-on" state which varies in intensity greatly from cycle to cycle, and then decays back to an "off" state at ∼ 1% of the peak main-on flux. This is followed by a rise to a weaker "short-on" state and then another low (Tananbaum et al 1972;Gorecki et al 1982). Superimposed on this cycle are eclipses of the neutron star by the companion once per orbit and dips that occur almost on the beat period between orbit and precession (Giacconi et al 1973), which are believed to be due to localized structure in the disk, generated by the impact of the ballistic gas stream from the L 1 point (Crosa & Bonton 1980;Schandl 1996).…”

Section: Introductionmentioning

confidence: 99%

Fine-Tuning the Accretion Disk Clock in Hercules X-1

Still

Boyd

2004

ApJ

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RXTE ASM count rates from the X-ray pulsar Her X-1 began falling consistently during the late months of 2003. The source is undergoing another state transition similar to the anomalous low state of 1999. This new event has triggered observations from both space-and ground-based observatories. In order to aid data interpretation and telescope scheduling, and to facilitate the phase-connection of cycles before and after the state transition, we have re-calculated the precession ephemeris using cycles over the last 3.5 years. We report that the source has displayed a different precession period since the last anomalous event. Additional archival data from CGRO suggests that each low state is accompanied by a change in precession period and that the subsequent period is correlated with accretion flux. Consequently our analysis reveals long-term accretion disk behaviour which is predicted by theoretical models of radiation-driven warping.

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HEAO 1 observations of the long-term variability of Hercules X-1

Cited by 13 publications

References 0 publications

The pulsed light curves of Her X–1 as observed by BeppoSAX

The pulsed light curves of Her X–1 as observed by BeppoSAX

Long-term cycles in cosmic X-ray sources

Fine-Tuning the Accretion Disk Clock in Hercules X-1

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