Superluminal Motion in CTA 102

Extract

Sholomitskii (1965) discovered that the flux density of the quasar CTA 102 varies at low frequencies on a timescale of a few months. Low-frequency variability can be explained by “superluminal flux variation” (Romney et al. 1984): If the intrinsic brightness of a component moving in a relativistically beamed source varies by only a few percent, the observer sees its flux density change by a much larger factor δ^3-α when the optically thin blob moves almost directly toward the observer. Such a relativistically beamed source is likely to exhibit superluminal motion if studied with sufficient resolution and sensitivity. Superluminal motion in CTA 102 was discovered by Bååth (1987) who concluded on the basis of maps made at three epochs at a frequency of 932 MHz that two components were separating at a rate of 0.65 milliarcseconds (mas) per year. Using a redshift z = 1.037 and H₀ = 100 km s⁻¹ Mpc⁻¹, q₀ = 0.5, this expansion speed corresponds to (18 ± 4)h⁻¹c. The extraordinarily high speed led us to make VLBI images of the source at a higher frequency in order to increase the resolution and make a more precise determination of the speed.