Restarted activity in the 3C328 radio galaxy. (arXiv:2104.13183v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Marecki_A/0/1/0/all/0/1">A. Marecki</a>
As a rule, both lobes of Fanaroff-Riley (FR) type-II radio sources are
terminated with hotspots, but the 3C328 radio galaxy is a specimen of an FR
II-like object with a hotspot in only one lobe. A conceivable reason for such
asymmetry is that the nucleus of 3C328 was temporarily inactive. There was no
energy transfer from it to the lobes during the period of quiescence, and so
they began to fade out. However, under the assumption that the axis connecting
the two lobes makes an appreciable angle with the sky plane, and hence one is
considerably farther from the observer than the other, the lobes are observed
at two distinct stages of evolution due to the light-travel lag. While the
far-side lobe is still perceived as being of the FR II type with a hotspot,
decay of the near-side lobe is already apparent. No jets are visible in the VLA
images, but the VLBA observations of the inverted-spectrum core component of
3C328 have revealed that it has a jet of a sub-arcsecond length pointing
towards the lobe that shows evidence of decay. Since the jet always points to
the near side, its observed orientation is in line with the scenario proposed
here. The presence of the jet supports the inference that the nucleus of 3C328
is currently active; however, given the fact that the jet is short (approx. 200
pc in projection), the activity must have restarted very recently. The lower
and upper limits of the quiescent period length have been calculated.
As a rule, both lobes of Fanaroff-Riley (FR) type-II radio sources are
terminated with hotspots, but the 3C328 radio galaxy is a specimen of an FR
II-like object with a hotspot in only one lobe. A conceivable reason for such
asymmetry is that the nucleus of 3C328 was temporarily inactive. There was no
energy transfer from it to the lobes during the period of quiescence, and so
they began to fade out. However, under the assumption that the axis connecting
the two lobes makes an appreciable angle with the sky plane, and hence one is
considerably farther from the observer than the other, the lobes are observed
at two distinct stages of evolution due to the light-travel lag. While the
far-side lobe is still perceived as being of the FR II type with a hotspot,
decay of the near-side lobe is already apparent. No jets are visible in the VLA
images, but the VLBA observations of the inverted-spectrum core component of
3C328 have revealed that it has a jet of a sub-arcsecond length pointing
towards the lobe that shows evidence of decay. Since the jet always points to
the near side, its observed orientation is in line with the scenario proposed
here. The presence of the jet supports the inference that the nucleus of 3C328
is currently active; however, given the fact that the jet is short (approx. 200
pc in projection), the activity must have restarted very recently. The lower
and upper limits of the quiescent period length have been calculated.
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