Soft X-ray excess in Seyfert galaxies
The soft excess is a ubiquitous feature in the X-ray spectra of Seyfert galaxies, a radio-quiet type of AGNs. It is observed as an excess over the low energy extrapolation of the 2-10 keV power-law. Its origin is an open question in AGN physics: it can be associated with reflection on the accretion disk, with a second Comptonization region, or with an absorption effect.
During my master thesis and part of the PhD I analyzed observations by the Suzaku X-ray satellite of two bright Seyferts: Markarian 509 and Markarian 841.
For further details see Cerruti, M., et al., “Suzaku broad-band observations of the Seyfert 1 galaxies Mrk 509 and Mrk 841“, A&A, 2011, 535, 113
Quasi-periodic oscillations in AGN light curves
The discovery of periodicities in the light curves of AGNs is of paramount importance. They could represent the sign of super-massive black-hole binaries, putting constraints on their evolution throughout the history of the Universe.
The Fermi satellite surveys the gamma-ray sky since 2009, collecting for the first time uninterrupted light curves of hundreds of AGNs. I supervised the work of Helena Ren, who uses wavelet analysis to identify quasi-periodicities in gamma-ray AGNs.
For further details see Ren, H.X., Cerruti, M., Sahakyan, N., “Quasi-periodic oscillations in the γ-ray light curves of bright active galactic nuclei“, A&A, 2023, 672, 86
Characterization and classification of gamma-ray bursts from blazars
Blazars are characterized by bright flaring episodes at all wavelengths. Despite extensive studies of individual events, there was not yet in the literature a systematic study of all flares to characterize their properties. I conducted the first comprehensive analysis of all blazar flares in the gamma-ray band (or, gamma-ray bursts from blazars, GRBBLs, or gerbils).
This first study shows that the GRBBL population is remarkably homogeneous. Unsupervised classification algorithms split the population into chromatic and achromatic GRBBLs with an evidence for a secondary classification on the basis of the peak luminosity.
For further details see Cerruti, M., “Characterization and classification of gamma-ray bursts from blazars“, A&A, 2025, 698, 101
Matteo Cerruti 