Abstract :
Accretion onto compact objects powers some of the most luminous and energetic phenomena in the Universe, from ultra-luminous X-ray sources (ULXs) and transient X-ray binaries to relativistic jets in blazars. Despite the vastly different mass scales and environments, these systems share a common challenge: interpreting their multiwavelength emission requires radiative models that are computationally expensive, often prohibitively so at the volumes demanded by modern surveys and Bayesian inference. In this talk I will present a coherent program addressing this challenge from both observational and methodological angles. I will first discuss recent results on super-Eddington accretion in ULXs and the role of magnetized neutron stars in this population. I will then turn to transient accretors in the Local Group — BeXRBs and transient ULXs — where time-domain monitoring with NICER, XMM-Newton, and NuSTAR allows direct probes of accretion physics through torque and pulse-profile modeling. Finally, I will describe ongoing work on neural-network emulators for lepto-hadronic blazar SED modeling (LeHaMoC, AM3), developed in collaboration with teams at NKUA, DESY, and APC, and outline how these methods can be extended to accreting pulsars, GRBs, and non-jetted AGN in preparation for NewAthena, eXTP, and the 2030s.
Short Bio: Georgios Vasilopoulos is a postdoctoral researcher at the Institute of Accelerating Systems and Applications (IASA) and the National and Kapodistrian University of Athens (NKUA), working on observational high-energy astrophysics with an emphasis on X-ray pulsars, ultra-luminous X-ray sources, and accretion under extreme conditions. He completed his PhD in 2018 at the Max Planck Institute for Extraterrestrial Physics and the Technical University of Munich, and subsequently held postdoctoral appointments at Yale University (2018–2021) and the Strasbourg Observatory/ CNRS (2021–2023), where he contributed to the XMM-Newton Survey Science Centre. Since 2023 he has been based in Athens, leading project ASTRAPE under a ELIDEK grant. He has contributed to more than 80 refereed publications, and has actively supervised and mentored students from the undergraduate to the PhD level. For his research he has secured observing time on most major modern X-ray observatories, including NICER, XMM-Newton, NuSTAR, Swift, and Chandra, which he routinely combines with multiwavelength data from ground- and space-based facilities. He has been a member of the science working groups for current and proposed missions like NewAthena, AXIS, HEX-P, SVOM, and STROBE-X, and contributes to public scientific tools including AMORA, LeHaMoC and BlazarML.
