RXTE Observations of Hercules X-1 During the July 1998 Short-high State

Abstract

We present RXTE monitoring of the eclipsing X-ray binary Hercules X-1 conducted over the short-high state of July 1998. This was one of the last major short-high states before the source entered an anomalous low-state of activity. A comparison with previous epochs finds no evidence for special behavior during these observations. We determine orbital and pulsar spin periods to facilitate measurements period derivatives during the subsequent anomalous low state and during the next epoch of high-state activity. Spectrally, the decay of the short-high state and concurrent pre-eclipse dips are consistent with obscuration of a central X-ray source by a cloud of non-uniform column density. The standard model of a warped accretion disk of finite vertical scale height fits the characteristics of this absorber well. Pre-eclipse dips have durations a factor of a few longer than the characteristic durations of dips during main-high states. Pulse profile structure increases in complexity towards the tail of the short-high state suggesting changes in accretion curtain geometry.

arXiv comment19 pages, 10 figures. ApJ, in press

References in corpus (6)

• First Results from the All-Sky Monitor on the Rossi X-ray Timing Explorer
• The 35-Day Evolution of the Hercules X-1 Pulse Profile: Evidence For A Resolved Inner Disk Occultation of the Neutron Star
• Warped Disks as a Possible Origin of Torque Reversals in Accretion-Powered Pulsars
• RXTE highlights of 34.85-day cycle of Her X-1
• Discovery of mHz UV Quasiperiodic Oscillations in Hercules X-1
• Hercules X-1: Empirical Models of UV Emission Lines

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• Suzaku Observations of Hercules X-1 : Measurements of the Two Cyclotron Harmonics
• Accretion disc viscosity: what do warped discs tell us?
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• XMM-Newton EPIC & OM observations of Her X-1 over the 35 day beat period
• Inversion of the decay of the cyclotron line energy in Her X-1
• X-ray Spectral Evolution of Her X-1 in a Low State and the Following Short High State
• A broad-band X-ray view of the precessing accretion disk and pre-eclipse dip in the pulsar Her X-1 with NuSTAR and XMM-Newton