The 1999 Hercules X-1 Anomalous Low State

W. Coburn; W. A. Heindl; J. Wilms; D. E. Gruber; R. Staubert; R. E. Rothschild; K. A. Postnov; N. Shakura; P. Risse; I. Kreykenbohm; M. R. Pelling

doi:10.1086/317081

arXiv · astro-ph/9911533

The 1999 Hercules X-1 Anomalous Low State

W. Coburn·W. A. Heindl·J. Wilms·D. E. Gruber·R. Staubert·R. E. Rothschild·K. A. Postnov·N. Shakura·P. Risse·I. Kreykenbohm·M. R. Pelling

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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.

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W. Coburn, W. A. Heindl, J. Wilms, D. E. Gruber, R. Staubert, R. E. Rothschild, K. A. Postnov, N. Shakura, P. Risse, I. Kreykenbohm, M. R. Pelling. 2000-06-16. The 1999 Hercules X-1 Anomalous Low State. https://doi.org/10.1086/317081

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