Probing Very Early Stage of Radio Source Evolution in NGC 1275 with VERA

TL;DR

This study uses VLBI observations to investigate the early evolution of a radio source in NGC 1275, revealing a new hot spot or radio lobe forming on sub-parsec scales that could influence gamma-ray emission.

Contribution

First detailed VLBI monitoring of a very young radio component in NGC 1275, identifying it as a nascent hot spot or radio lobe at an early evolutionary stage.

Findings

C3 is a newly formed hot spot or radio lobe.

C3's apparent velocity is consistent with young radio sources.

Radio flux and size of C3 increased while maintaining optically-thin spectra.

Abstract

We report on VLBI observations of NGC 1275 with VLBI Exploration of Radio Astrometry (VERA) and Very Long Baseline Array (VLBA) during 2008 and 2013 at 15, 22 and 43 GHz. Our observations provide long-term variations in the radio flux and structure of the inner jet in NGC 1275 on sub-parsec scales, particularly at C3 which is a new radio component accountable for the recent active state in radio regime since early-2000s. We found the apparent velocity of C3 was $\beta_{\rm{app}} = 0.267 \pm 0.007 $, which was consistent with typical velocities of the hot spot and/or radio lobes in the young radio sources. Furthermore, the radio flux and size of C3 had simultaneously increased during September 2007 and May 2012 with keeping optically-thin spectra, suggesting that the particle acceleration occurred inside C3 as generally seen in the hot spots of the radio lobes. Our new observations suggest that C3 is a new-born hot spot and/or radio lobe at a very early stage of its evolution. Our results imply the radio lobes in the radio galaxies might be already formed on sub-parsec scales from the central SMBH and might play an important role to produce $\rm \gamma$-ray emission in the young radio sources.