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Simultaneous hard X-ray and optical observations of Sco X-1 and a model of semi-opaque X-ray sources

Abstract

Simultaneous observations of hard X-ray and optical emission from Sco X-1 were carried out at Hyderabad, India, on April 16 and 19, 1972. During the first and the second observations Sco X-1 was on the average in a bright phase ofB=12.5 mag. and a slightly darker phase ofB=12.7 mag. respectively. During the first observation the X-ray intensity in the energy range 20–40 keV measured with balloon borne scintillation counters showed an enhancement of a factor of about two in coincidence with an optical flare ofB≅0.2 mag., whereas the apparent temperature derived from the X-ray spectrum observed in the energy range 20–35 keV showed no appreciable change. Both the X-ray intensity and the apparent temperature observed on April 19 are considerably lower than those observed on April 16. Taking into account the effect of radiative transfer in a hot plasma, the electron density and the optical depth for electron scattering of the plasma cloud are derived asn e ≈3×1016 cm−3 and τes ≈ 10 for the quiescent bright phase. The flare is explained by an increase of the plasma mass by about 30% and an increase of τes by τes ≈ 1 without appreciable change of the plasma temperature. The results on April 19 is interpreted as indicating that the quiescent dark phase may be characterized by a decrease of the plasma mass, its contraction and lower temperature.

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Kasahara, I. Simultaneous hard X-ray and optical observations of Sco X-1 and a model of semi-opaque X-ray sources. Astrophys Space Sci 29, 191–210 (1974). https://doi.org/10.1007/BF00642723

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Keywords

  • Flare
  • Energy Range
  • Radiative Transfer
  • Optical Depth
  • Optical Emission