An optical perspective on early-stage AGN with extreme radio flares

TL;DR

This study analyzes optical spectra of radio-flaring NLS1 galaxies to identify common features, finding typical NLS1 properties but no direct optical indicators of their extreme radio activity, suggesting the need for multi-wavelength research.

Contribution

It provides the first optical emission line analysis of radio-flaring NLS1 galaxies, linking optical properties with radio behavior and highlighting the complexity of their phenomena.

Findings

Most sources have typical NLS1 properties.

Black hole masses are above 10^7 solar masses.

Optical spectra do not reveal the radio flaring phenomenon.

Abstract

In the last decade of Active Galactic Nuclei (AGN) monitoring programs, the Mets\"ahovi Radio Observatory detected multiple times seven powerful flaring narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz. Several hypotheses have been proposed, but the understanding of this unique phenomenon is still far. To look at the case from a different point of view, we performed an emission line analysis of the optical spectra, with the aim of identifying similarities among the sources, that can be in turn possibly tied with the radio behavior. Our data were obtained with the Gran Telescopio Canarias. The results we obtained show that six out of seven sources have typical properties for the NLS1 class, and one of them is an intermediate Seyfert galaxy. We found on average black hole masses above the median value for the class (> 10$^7$ M$_\odot$), and a strong Fe II emission, which could be a proxy for an intense ongoing accretion activity. Although interesting, the characteristics we found are not unusual for these kind of AGN: the optical spectra of our sources do not related with their unique radio properties. Therefore, further multi-wavelength studies will be necessary to narrow the field of hypotheses for this peculiar phenomenon.