The latest puzzle in narrow-line Seyfert 1 galaxies: invisible jets?

Main Colloquium
Dr. Marco Berton
European Southern Observatory, Santiago, Chile

Narrow-line Seyfert 1 (NLS1) galaxies are a subclass of active galactic nuclei (AGN) identified more than 30 years ago, but still not entirely understood. These objects are likely characterized by rapidly growing low-mass black holes. Interestingly enough, some of them have been detected in gamma-rays, a sign that they can harbor powerful relativistic jets. In my talk I will review their properties, showing how the true nature of NLS1s is that of early-stage AGN in a recently triggered activity phase, and how they are connected to other classes of kinematically young jetted AGN. I will also report on the discovery, in a handful of NLS1s, of relativistic jets remarkably faint at low radio frequency, but extremely bright and variable at high radio frequency. New observations of these sources are revealing an increasingly complicated picture, and I will outline the different scenarios we are developing to explain this new, unexpected phenomenon.

The Renaissance of Astrophysics: a landscape of opportunities in the era of Time Domain Multi-Messenger investigations

Special Colloquium
Prof. Raffaella Margutti
Northwestern University, Evanston, Illinois, USA

Astronomical transients are signposts of catastrophic events in space, including the most extreme stellar deaths, stellar tidal disruptions by supermassive black holes, and mergers of compact objects. Thanks to new and improved observational facilities we can now sample the night sky with unprecedented temporal cadence and sensitivity across the electromagnetic spectrum and beyond. This effort has led to the discovery of new types of astronomical transients, revolutionized our understanding of phenomena that we thought we already knew, and enabled the first insights into the physics of neutron star mergers with gravitational waves and light. In this talk I will review some very recent developments that resulted from our capability to acquire a truly panchromatic view of transient astrophysical phenomena. I will focus on two key areas of ignorance in the field: (i) What are the progenitors of stellar explosions and what happens in the last centuries before death? (ii) What is the nature of the compact objects produced by these explosions and what happens when compact objects merge? The unique combination of Discovery Power (guaranteed by planned transient surveys across the electromagnetic spectrum, combined with efforts in the realm of artificial intelligence) and Understanding (enabled by multi-messenger observations) is what positions time-domain astrophysics for major advances in the near future.