ar X iv : a st ro - p h / 99 11 53 3 v 1 3 0 N ov 1 99 9 The 1999 Hercules X - 1 Anomalous Low State

A failed main-on in the 35 d cycle of Her X-1 was observed with the Rossi X-ray Timing Explorer (RXTE ) on 1999 April 26. Exceptions to the normal 35 d 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 2.5-20 keV band with a pulsed fraction of (4.7 ± 0.2)%. 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 (nH = 5.6 × 10 23 cm). 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 d cycle.