Origin of the ring structures in Hercules A, sub-arcsecond 144 MHz to 7 GHz observations

Monday 2 May 2022, 13:30 → 13:50 Europe/Rome

0/0-1 - Aula A (Dipartimento di Fisica e Astronomia - Edificio ex-Rizzato)

Speakers: Silvio Di Rosa (Università degli Studi di Padova)

The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensivelystudied sources in the radio sky, the origin of the ring structures in the Hercules A radio lobes remains an open question. We presentthe first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFARTelescope. With the addition of data from theKarl G. JanskyVery Large Array, we mapped the structure of the lobes from 144 MHzto 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described bya shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the ringsare formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of thedifferent ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shapeof the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from thedeposition of material from past periods of intermittent core activity.

aa40880-21.pdf

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