On October 9, 2022, the Earth was flashed for ten minutes by GRB221009A, the brightest and one of the longest gamma-ray bursts yet observed since the birth of gamma-ray astronomy 50 years ago. The gamma-ray (keV to MeV energy band) flux was so intense that it saturated almost all of the detectors aboard a number of space missions. Remarkably, it caused a sudden ionospheric disturbance in the lower layers of the Earth's sunlit ionosphere (60-100 km in altitude). The exceptional nature of this event was the result of two rare properties: (i) among the most luminous and energetic ever, and (ii) at redshift z=0.151, so relatively close to us (among the 4% nearest ones out of ~600 events with measured distance).
The unparalleled quality of the data sets collected from numerous space and ground based observatories, encompassing the gamma-ray prompt as well as the afterglow emission (from radio all the way up to the record-breaking value 18 TeV), represents an unprecedented challenge to modelling. As a consequence, no  consensus was obtained on some of the key aspects, such as the jet opening angle: was it a truly energetic event with a typical opening angle, or a more ordinary energy release collimated into an exceptionally narrow jet? Can the afterglow theory account for the radio-to-hard energy data set in a self-consistent way? How could a 18-TeV photon escape pair creation along the way due to extra-background light and what are the possible implications?
In this talk I will discuss some of the challenges posed by a truly unique event, which will presumably stay in the spotlight for many years to come.

Breve CV del Prof. Dr. Cristiano Guidorzi:

After carrying out the PhD at the University of Ferrara on the GRBs detected with the former game changer Italian BeppoSAX mission, a few months before the launch of Swift he got a Marie Curie fellowship at the Astrophysical Research Institute of the Liverpool John Moores University (UK), where he contributed to the GRB pipeline of the 2-m robotic Liverpool Telescope and its data analysis, and interpretation. Among the numerous GRB early afterglow light curves (LC), this project harvested the first early multi-colour data sets and the first early optical polarimetric measurements, which constrained the nature of the relativistic outflows in GRB jets. A few years later he joined the Italian Swift team at the Brera Observatory in Milan as a research associate and kept working on the broadband modelling of GRBs. In 2009 he moved to the University of Ferrara, where he is currently associate professor and chair of "Astrophysical Processes" and "Multimessenger Astrophysics" courses for the Master's Degree. Recently, he developed an interest in the quest for high-energy emission associated with elusive fast radio burst sources and joined an on-going multi-wavelength campaign with several INAF research staff. Member of different international collaborations, in 2019 he joined the GRB group of the first Chinese X-ray mission Insight-HXMT (launched 2017) and contributed to the first GRB catalogue of this mission as well as to the analysis and interpretation of the unique data set collected on GRB221009A.