Unveiling the X-ray Secrets of Fermi-detected Narrow-Line Seyfert 1 Galaxies with XMM-Newton Observations

Abstract

In the innermost regions of active galactic nuclei, where the accretion disk, corona, and jet processes are closely coupled, X-ray observations offer a direct probe to study the physics of disk-jet coupling and the mechanisms driving relativistic outflows. We present a comprehensive analysis of the X-ray timing and spectral variability of 16 Narrow Line Seyfert 1 galaxies detected by Fermi-LAT, based on 29 epochs of XMM-Newton observations. A moderate intraday flux variability is observed throughout the sample, with fractional variability ranging from 5 to 16\%. The temporal study of 1H\,0323+342 reveals a distinctive turnover timescale in structure functions, along with notable variations in flux and power spectral density slopes. The hardness ratio in some epochs demonstrates a clear trend of softer-when-brighter. The X-ray spectra of 1H 0323+342, PMN J0948+0022, RGB J1644+263, PKS 1502+036, and J1246+0238 are well fitted by a power-law + blackbody model, suggesting a bright disk along with a jet, and J1222+0413 is fitted by broken power-law, while the remaining sources are well fitted by a power-law model revealing the non-thermal domination. The X-ray luminosity exhibits a strong correlation with $γ$-ray and disk luminosity, and a strong correlation with the jet power, suggesting a close coupling of disk and jet. Additionally, we have found an anti-correlation between the X-ray spectral index and the X-ray luminosity, as well as with the FWHM of H$β$ line, indicating a complex interaction between the central engine, jet activity, and the accretion disk in these sources.