Multiple Wavelength Variability and Quasi-Periodic Oscillation of PMN J0948+0022

TL;DR

This paper analyzes multi-wavelength data of the narrow-line Seyfert 1 galaxy PMN J0948+0022, revealing flux variability, correlations, and a quasi-periodic oscillation, and discusses potential mechanisms including gravitational waves.

Contribution

It provides the first comprehensive multi-wavelength analysis of PMN J0948+0022, identifying a QPO and exploring its possible origins, which advances understanding of such galaxies.

Findings

Significant flux variations across gamma-ray, X-ray, optical, and radio bands.

Detection of a ~490-day QPO in gamma-ray and optical lightcurves.

Gamma-ray flux correlates with V-band flux with a ~44-day lag.

Abstract

We present a comprehensive analysis of multiple wavelength observational data of the first GeV-selected narrow-line Seyfert 1 galaxy PMN J0948+0022. We derive its lightcurves in the \gamma-ray and X-ray bands from the data observed with Fermi/LAT and Swift/XRT, and make the optical and radio lightcurves by collecting the data from the literature. These lightcurves show significant flux variations. With the LAT data we show that this source is analogue to typical flat spectrum radio quasars in the $L_\gamma-\Gamma_\gamma$ plane, where $L_\gamma$ and $\Gamma_\gamma$ are the luminosity and spectral index in the LAT energy band. The gamma-ray flux is correlated with the V-band flux with a lag of ~44 days, and a moderate quasi-periodic oscillation (QPO) with a periodicity of ~490 days observed in the LAT lightcurve. A similar QPO signature is also found in the V-band lightcurve. The gamma-ray flux is not correlated with the radio flux in 15 GHz, and no similar QPO signature is found in a confidence level of 95%. Possible mechanisms of the QPO are discussed. We propose that gravitational wave observations in the future may clarify the current plausible models for the QPO.