The 1999 Hercules X-1 anomalous low state

A failed main-on in the 35 day cycle of Her X-l was observed with the Rossi X-Ray Timing Explorer on 1999 April 26. Exceptions to the normal 35 day cycle have been seen only twice before-in 1983 and again in 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 = 5.0 x 10(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 35 day cycle.