• Observation of ultra low hard X-ray flux from Cyg X-1 —A possible partial occulation of the X-ray source

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      https://www.ias.ac.in/article/fulltext/joaa/022/01/0009-0020

    • Keywords

       

      Accretion, accretion disks; X-rays: stars; black hole candidate: individual; Cyg X-1

    • Abstract

       

      The black hole candidate Cyg X-1 was observed in ultra low state on march 30, 1997 using Large Area Scintillation counter Experiment (LASE) in the hard X-ray energy region of 20–180 keV. During the 30 minute exposure a combined signal of 68 sigma was obtained, however, the measured flux at 50 keV was lower by a factor of 2 than the minimum flux reported so far. Using the recent orbital ephemeris of the source, our snap-shot observations were made at ϕ5.6 = 0.915, which corresponds to the binary minimum revealed by the ASM light curves. The daily average data from the BATSE detectors give the source intensity level to be higher by a factor of 5. Very low flux values measured in the present experiment suggest that the hard X-ray source may have been partially occulted by the primary companion during its transit near the X-ray minimum.

    • Author Affiliations

       

      R. K. Manchanda1

      1. Tata Institute of Fundamental Research, Colaba, Mumbai - 400 005, India
    • Dates

       
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