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19 April 2024 |
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X-ray observations during a Her X-1 anomalous low-state | | A.N. Parmar
; T. Oosterbroek
; D. Dal Fiume
; M. Orlandini
; A. Santangelo
; A. Segreto
; S. Del Sordo
; | | Date: |
2 Sep 1999 | | Subject: | astro-ph | | Affiliation: | ESA/ESTEC, ITESRE/Bologna, IFCAI/Palermo | | Abstract: | Results of a 1999 July 8-10 BeppoSAX observation during an anomalous low-state of Her X-1 are presented. The standard on-state power-law and blackbody continuum model is excluded at high confidence unless partial covering is included. This gives a power-law photon index of 0.63 +/- 0.02 and implies that 0.28 +/- 0.03 of the flux undergoes additional absorption of (27 +/- 7) 10^22 atom/cm2. 11% of the observed 0.1-10 keV flux is from the 0.068 +/- 0.015 keV blackbody. 1.237747(2) s pulses with a semi-amplitude of 2.1 +/- 0.8% are detected at >99.5% confidence and confirmed by RXTE measurements. This implies that Her X-1 underwent substantial spin-down close to the start of the anomalous low-state. The spectral and temporal changes are similar to those recently reported from 4U1626-67. These may result from a strongly warped disk that produces a spin-down torque. The X-ray source is then mostly viewed through the inner regions of the accretion disk. A similar mechanism could be responsible for the Her X-1 anomalous low-states. Shadowing by such an unusually warped disk could produce observable effects in the optical and UV emission from the companion star. | | Source: | arXiv, astro-ph/9909039 | | Services: | Forum | Review | PDF | Favorites | |
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