# Intra-day variability of three Seyfert Galaxies measured with XMM-Newton

## TL;DR

This study analyzes intra-day X-ray variability in three Seyfert galaxies using XMM-Newton data, revealing characteristic timescales, spectral softening during flares, and providing new black hole mass estimates.

## Contribution

It offers a uniform analysis of long XMM-Newton observations, identifying variability timescales and spectral behavior, and estimates black hole masses supporting the small black hole hypothesis for NLS1 galaxies.

## Key findings

- Characteristic variability timescales between 2.9 ks and 45.3 ks.
- Hard and soft X-ray bands are well correlated.
- Sources soften during flares.

## Abstract

We present and analyze the variability of three Seyfert galaxies on intra-day timescales. We have analyzed in a uniform manner the 38 longest ( $>30$ ks) observations made for NGC 4051, MCG$-06-30-15$ and NGC 4151 by XMM-Newton between 2000 and 2015. The nuclei were quite active during essentially all of these observations and the overall X-ray fluxes (0.3-10 keV) varied by an order of magnitude. Most of the observations do appear to show characteristic timescales, estimated through their auto-correlation functions, ranging between $\sim 2.9$ ks and $\sim 45.3$ ks. The hard (2-10 keV) and soft (0.3-02 keV) bands are very well correlated but consideration of their hardness ratios show that the sources typically soften during flares. We also provide new estimates of the central black hole masses for these three AGN that support the hypothesis that Narrow Line Seyfert 1 galaxies have relatively small central black holes.