Discovery of Optical Emission in the Hot Spots of Three 3CR Quasars: High-Energy Particle Acceleration in Powerful Radio Hot Spots

Archival Hubble Space Telescope WFPC2 images were used to search for optical emission associated with the radio jets of a number of luminous quasars. From this search, we report new optical hot spot detections in the well-known blazar 3C 454.3 and the lobe-dominated quasars 3C 275.1 and 3C 336. We also find optical emission in the vicinity of the hot spot in 3C 208 but believe this is a chance alignment. Optical emission from the arcsecond-scale jet in 3C 454.3 is also detected. Multifrequency archival radio data from the VLA and MERLIN are analyzed, and the synchrotron spectra of these high-power hot spots are presented. We estimate that their break frequencies are in the range of 10 super(10)-10 super(11) Hz, with large uncertainties due to the wide gap in frequency coverage between the radio and optical bands. We also calculate their equipartition magnetic fields and find that the anticorrelation between break frequency and magnetic field found by Brunetti et al. for lower power hot spots extends to these high-power hot spots. This supports their model of hot spots based on shock acceleration and synchrotron losses.