The X-ray variability and the near-IR to X-ray spectral energy distribution of four low luminosity Seyfert 1 galaxies

TL;DR

This study investigates the X-ray variability and spectral energy distribution of four low-luminosity Seyfert 1 galaxies, finding their properties similar to more luminous AGN, suggesting similar accretion processes operate across luminosities.

Contribution

It provides new insights into the spectral and variability characteristics of low-luminosity Seyfert galaxies, indicating that efficient accretion mechanisms may persist at low accretion rates.

Findings

X-ray variability matches expectations based on black hole mass.

Near-IR to X-ray spectra resemble those of much more luminous quasars.

Low-luminosity Seyferts host unobscured, AGN-like nuclei.

Abstract

We present the results from a study of the X-ray variability and the near-IR to X-ray spectral energy distribution of four low-luminosity, Seyfert 1 galaxies. We compared their variability amplitude and broad band spectrum with those of more luminous AGN in order to investigate whether accretion in low-luminosity AGN operates as in their luminous counterparts. We used archival XMM-Newton and, in two cases, ASCA data to estimate their X-ray variability amplitude and determine their X-ray spectral shape and luminosity. We also used archival HST data to measure their optical nuclear luminosity, and near-IR measurements from the literature, in order to construct their near-IR to X-ray spectra. The X-ray variability amplitude of the four Seyferts is what one would expect, given their black hole masses. Their near-IR to X-ray spectrum has the same shape as the spectrum of quasars which are 10^2-10^5 times more luminous. The objects in our sample are optically classified as Seyfert 1-1.5. This implies that they host a relatively unobscured AGN-like nucleus. They are also of low luminosity and accrete at a low rate. They are therefore good candidates to detect radiation from an inefficient accretion process. However, our results suggest that they are similar to AGN which are 10^2-10^5 times more luminous. The combination of a "radiative efficient accretion disc plus an X-ray producing hot corona" may persist at low accretion rates as well.