Calendario Dottorato

Dottorato in Fisica

Journal Club Seminari 2025

16/10/2025  
aula 72

ore: 16:00	Lai Alessandro Leonardo DOTTORATO IN FISICA	Probing the Variable Soft Excess in Luminous Quasars: A Two-Corona Approach to PG 1407+265 and RBS 229
		Active Galactic Nuclei (AGN) are among the brightest objects in the Universe and provide a unique environment to study accretion onto supermassive black holes. Quasars, in particular, stand out for their high luminosities and cosmological reach, making them powerful probes of both astrophysical processes and the distant Universe. A key but still poorly understood feature of many AGN is the Soft Excess (SE), an excess of low-energy X-ray emission whose physical origin remains debated. PG 1407+265 represents a particularly intriguing case, as it shows a strongly variable SE extending up to ~3 keV. Together with RBS 229, it has been analyzed using a two-corona Comptonization model, combining optical/UV and X-ray data to disentangle the physical components responsible for the emission. This approach allows us to characterize the warm and hot coronae and to investigate their evolution across different epochs. These properties make PG 1407+265 and RBS 229 valuable laboratories for understanding AGN emission and for exploring the behavior of αOX, a key parameter linking the UV and X-ray emission in quasars and their potential use as cosmological tools.

ore: 16:30	Ferretti Federico DOTTORATO IN FISICA	Tracing the Inner Flow: Variability and QPOs in Black-Hole X-ray Binaries
		Black-hole X-ray binaries (BHXRBs) represent ideal laboratories to study accretion and ejection processes under extreme gravity. Their emission, variable over a wide range of timescales, reveals a tight connection between the accretion flow and relativistic outflows. X-ray timing studies have shown that quasi-periodic oscillations (QPOs) are a key signature of the inner accretion flow dynamics. These features, observed across different spectral states, provide crucial constraints on the geometry and physical mechanisms at play close to the event horizon. In this presentation I will review the main phenomenology of QPOs in BHXRBs, discussing their classification, observational properties, and the leading models proposed to explain their origin