65 research outputs found
The Fate of Dead Radio-loud Active Galactic Nuclei: A New Prediction of Long-lived Shell Emission
We examine the fate of a dead radio source in which jet injection from the
central engine has stopped at an early stage of its evolution ( yr). To this aim, we theoretically evaluate the evolution of the
emission from both the lobe and the shell, which are composed of shocked jet
matter and a shocked ambient medium, respectively. Based on a simple dynamical
model of expanding lobe and shell, we clarify how the broadband spectrum of
each component evolves before and after the cessation of the jet activity. It
is shown that the spectrum is strongly dominated by the lobe emission while the
jet is active (). On the other hand, once the jet activity has
ceased (), the lobe emission fades out rapidly, since fresh electrons
are no longer supplied from the jet. Meanwhile, shell emission only shows a
gradual decrease, since accelerated electrons are continuously supplied from
the bow shock that is propagating into the ambient medium. As a result, overall
emission from the shell overwhelms that from the lobe at wide range of
frequencies from radio up to gamma-ray soon after the jet activity has ceased.
Our result predicts a new class of dead radio sources that are dominated by
shell emission. We suggest that the emission from the shell can be probed in
particular at a radio wavelengths with the Square Kilometer Array (SKA) phase
1.Comment: 9 pages, 3 figures, accepted for publication in Ap
The young radio lobe of 3C 84: inferred gas properties in the central 10 parsec
We analyse the environment of the supermassive black hole (SMBH) in the
centre of a massive elliptical galaxy NGC 1275 in the Perseus cluster, hosting
the radio source 3C 84. We focus on the young radio lobe observed inside the
estimated Bondi accretion radius. We discuss the momentum balance between the
jet associated with the lobe and the surrounding gas. The results are compared
with the proper motion of the radio lobe obtained with the very long baseline
interferometry. We find that under assumption of a high-density environment >~
100 cm^-3), the jet power must be comparable to the Eddington luminosity ---
this is clearly inconsistent with the current moderate activity of 3C 84, which
indicates instead that the jet is expanding in a very low density region (<~1
cm^-3), along the rotation axis of the accretion flow. The power required for
the jet to expand in the low-density environment is comparable to the past
average jet power estimated from the X-ray observations. We estimate the
classical Bondi accretion rate, assuming that (1) gas accretion is spherically
symmetric, (2) accretion is associated with the jet environment, and (3) the
medium surrounding the jet is representative of the properties of the dominant
accreting gas. We find that Bondi accretion is inconsistent with the estimated
jet power. This means that either accretion of the cold gas in the NGC 1275 is
more efficient than that of the hot gas, or the jets are powered by the SMBH
spin.Comment: Replaced with published versio
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