Simultaneous hard X-ray and optical observations of Sco X-1 and a model of semi-opaque X-ray sources |
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Authors: | Izumi Kasahara |
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Institution: | (1) Dept. of Physics, Nagoya University, Nagoya, Japan |
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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 es 10 for the quiescent bright phase. The flare is explained by an increase of the plasma mass by about 30% and an increase of es by es 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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