The 1999 Hercules X-1 Anomalous Low State

Abstract

A failed main-on in the 35d cycle of Her X-1 was observed with the Rossi X-Ray Timing Explorer (RXTE) on 1999 April 26. Exceptions to the normal 35d cycle have been seen only twice before; in 1983 and again 1993. We present timing and spectral results of this latest Anomalous Low State (ALS) along with comparisons to the main-on and normal low states. Pulsations were observed in the 3-18 keV band with a fractional RMS variation of (0.037+-0.003). Spectral analysis indicates that the ALS spectrum has the same shape as the main-on but is modified by heavy absorption and scattering. We find that 70% of the observed emission has passed through a cold absorber (N_H=5.0x10^{23}cm^{-2}). This partially absorbing spectral fit can be applied to the normal low state with similar results. We find that the ALS observations may be interpreted as a decrease in inclination of the accretion disk causing the central X-Ray source to be obscured over the entire 35d cycle.

revised text, 6 revised figures, accepted for publication in ApJ

References in corpus (4)

• Observations of Accreting Pulsars
• In-flight Performance of the High Energy X-ray Timing Experiment 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
• RXTE highlights of 34.85-day cycle of Her X-1

Cited by in corpus (22)

• Origin of the Soft Excess in X-ray Pulsars
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• Variable neutron star free precession in Hercules X-1 from evolution of RXTE X-ray pulse profiles with phase of the 35-day cycle
• Accretion disc viscosity: what do warped discs tell us?
• XMM-Newton EPIC observations of Her X-1
• Probing the outer edge of an accretion disk: A Her X-1 turn-on observed with RXTE
• Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545
• XMM-Newton EPIC & OM observations of Her X-1 over the 35 day beat period
• Fine-tuning the accretion disk clock in Hercules X-1
• Continued decay in the cyclotron line energy in Hercules X-1
• A BeppoSAX observation of Her X-1 during the first main-on after an anomalous low-state: evidence for rapid spin-down
• Inversion of the decay of the cyclotron line energy in Her X-1
• Analysis of RXTE-PCA Observations of SMC X-1
• Atmospheric reflection during an anomalous low-state of Hercules X-1
• Discovery of Coupling between Periodic and Aperiodic Variability and X-ray Quasi-periodic Oscillations from Her X-1
• Spectral Signature of Atmospheric Reflection in Hercules X-1/HZ Hercules During Low and Short-High States
• Timing and X-ray Spectral Features of Swift J1626.6-5156
• 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
• Swift/BAT and RXTE/ASM Observations of the 35-day X-ray Cycle of Hercules X-1
• Evidence for neutron star triaxial free precession in Her X-1 from Fermi/GBM pulse period measurements
• Modeling of 35-day superorbital cycle of $B$ and $V$ light curves of IMXB HZ Her/Her X-1