The 1982 September radio outburst of Cygnus X-3 - Evidence for jetlike emission expanding at not less than about 0.35 C

Abstract

The angular size of Cyg X-3 was measured at 20, 6, 2, and 1.3 cm, 10 and 21 days after a strong outburst occurred within one day of September 28, 1982. From the 1.3 and 2 cm source sizes and the date of the outburst, the expansion velocity was found to be 0.010 + or - 0.002 arcsec per day along a position angle of approximately 0 deg. The energy transport mechanism in Cyg X-3 may be similar to that in SS 433 since the ratio of major to minor axes at 1.3 and 2 cm is 4:1. If the source is at a distance in excess of 11.6 kpc, the inferred expansion speed is not less than about 0.35 c. At wavelengths longer than 6 cm, the source size varies as lambda-squared, suggesting scattering due to local thermal plasma inhomogeneities.