Some Possible Implications of the Radio Emission of Sco X-1

Abstract

Recent observations of radio emission from Sco X-1 at centimeter wavelengths by Andrew and Purton (1968) and by Ables (1969) have added an important new dimension to the study of galactic X-ray sources. We have considered two alternative interpretations of the radio emission from this object. First, we discuss whether it is possible to attribute the radio emission of Sco X-1 to thermal bremsstrahlung from an optically thin plasma at a temperature of 15 to 20 keV. This interpretation would have the merit of relating the radio properties to the existence of a hot, flaring plasma component whose presence has been invoked to explain the observations of hard X-rays (≳ 35 keV) from this object (Peterson and Jacobson, 1966, Buselli et al., 1968, Riegler et al., 1968, Riegler, 1969, Agrawal et al., 1969a, McCracken, 1969). That the 6-cm radio emission and the hard X-radiation should be found to vary by similar amounts over similar time scales lends this hypothesis a certain appeal. However, the measurement at 11 cm of flux density amounting to ≈0.07 flux units (1 flux unit ≡ ≡ 10−23 erg cm−2 sec−1 Hz−1) reported at this Symposium by McCracken makes it virtually untenable to regard the radio emission of Sco X-1 as arising from thermal origins. Excessive optical and infrared continuum radiation would be produced; moreover, the shape of the radio spectrum is inconsistent with any conceivable thermal model. An explanation for the radio emission of Sco X-1 must therefore be sought in terms of some non-thermal radiation mechanism.