Hot Spots



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Hot Spots

Hot spots are the supposed termination regions of jets and may be sites of extranuclear particle reacceleration in radio sources. There have recently been reports of systematic side-to-side differences between jetted and counterjetted hot spots, particularly in 3CR quasars, including differences in compactness and placement in the lobes, and, most surprisingly, extended regions of somewhat flatter high-frequency spectra around the jetted hot spots. These studies suggest that whatever induces the asymmetry between the brighter and fainter jets in such sources extends at least as far as the hot spots, and perhaps beyond them. If the relativistic-jet model is correct, this implies that some bulk relativistic flow persists into the radio lobes. This greatly increases interest in detailed imaging and continuum spectroscopy of jetted and counterjetted hot spots at high frequencies. The only hot spot structures that have been fully resolved by the current VLA are in nearby radio galaxies such as Cygnus A and Pictor A. To resolve the physically-interesting structures in the hot spots of distant radio galaxies or quasars we must increase the angular resolution beyond that obtainable now with the VLA by increasing the u-v baselines, not by going to higher observing frequencies. Ideally, we need scaled-array capability at resolutions of order from 0.6 to 40 GHz, with enough sensitivity at the higher frequencies to determine the spectra of the more emission associated with the hot spots. This requires high bandwidth at the high frequencies, and the A+ configuration (plus cross-linking to the VLBA) at the low frequencies.



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