High Observed Brightnesses in Radio Jets
arXiv:astro-ph/9808207 · doi:10.1086/306679
Abstract
We study the variability properties at radio frequencies of the jets thought to be typical of Active Galactic Nuclei, i.e. bulk Lorentz factor Γ~ 10, and incoherent synchrotron emission. We assume that the radiating electrons are accelerated at shocks within the jet, and that these shocks have a suitable (conical) geometry. In our framework, we can reproduce the variability pattern of Intra Day Variables (20% in less than 1 day) as long as the observed brightness temperature is T_B < 3x10^{17} K. The only stringent condition is an injection timescale of the perturbation shorter than the variability timescale; the geometric condition on the viewing direction is not especially severe, and agrees with the observed occurrence of the phenomenon. For higher values of T_B coherent processes are probably necessary.
12 pages, aaspp4 style, accepted ApJ Part 1
References in corpus (5)
Cited by in corpus (13)
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