A Radio Quasi-periodic Oscillation of 176 day in the Radio-loud Narrow-line Seyfert 1 Galaxy J0849+5108

TL;DR

This study reports a 176-day quasi-periodic oscillation in the radio light curve of the radio-loud NLSy1 galaxy J0849+5108, observed over 11 years, with implications for jet or accretion disk dynamics.

Contribution

First detection of a long-term radio QPO in a NLSy1 galaxy, providing insights into jet or accretion disk mechanisms in AGN.

Findings

Radio QPO detected at >5σ significance

QPO lasted for 21 cycles, disappearing after Jan 2019

No corresponding gamma-ray QPO observed

Abstract

We analyze the 11-year long-term light curve of the Radio-loud Narrow-line Seyfert 1 (NLSy1) galaxy J0849+5108 and the nearly simultaneous $\gamma$-ray data of the source. The data were obtained with the Owens Valley Radio Observatory 40-m telescope at 15~GHz and with the Large Area Telescope onboard Fermi Gamma-ray Space Telescope, respectively. A quasi-periodic oscillation (QPO) signal at a significance of $>$5$\sigma$ is found in the radio light curve, but no similar modulation is seen in the $\gamma$-ray light curve. The QPO signal was present for 21 cycles, the longest among the reported radio QPOs, and likely disappeared after 2019 January 16. Different mechanisms proposed to explain the observed QPOs in Active Galactic Nuclei (AGN) are discussed for this QPO case. Either a secular instability in the inner accretion disk or a helical structure in the jet of J0849+5108 may explain the radio QPO, while for the latter scenario the jet has to be collimated up to $\sim$200~pc, similar to that seen in the nearby AGN M87. It will be of interests to keep monitoring the source at radio frequencies, seeing if similar QPO signals would appear again or not.