Colloquium
High-energy blazar emission through multi-wavelength polarimetry and synergies with VHE observations

Dr. Jorge Otero Santos
See the live streaming of this talk on Thursday May 28, 10:30 GMT+1).

Abstract

Blazars, active galactic nuclei with a relativistic jet pointing towards the Earth, are some of the brightest objects in the Universe. Their emission, extending from radio to gamma rays, is intrinsically polarized due to the emission processes involved. In fact, polarimetry has been key for studying these jets and their magnetic fields. The recent launch of the novel NASA/ASI IXPE X-ray polarimeter has opened a new window of observation thanks to its high-energy polarimetric capabilities. During its first years of operation, multi-wavelength polarimetry has proven to be a powerful tool for identifying the structure of blazar jets and the dominant particle acceleration mechanisms in them.

In this talk I will present the capabilities of multi-wavelength and high-energy polarimetry towards the understanding of AGN physics through the practical example of the recent results obtained during a campaign on blazar BL Lacertae (BL Lac) by IXPE. This campaign was complemented with multi-spectral-range observations with large millimeter, radio and optical polarimeters, resulting in the detection of the most polarized blazar ever observed. More interestingly, the combination of radio, optical and X-ray polarimetry has allowed us to identify, for the first time, the dominant process responsible for the X-ray emission of a blazar, ruling out hadronic processes as the main drivers of X-ray radiation from BL Lac. These results open the way to future multi-wavelength polarimetric studies with upcoming instruments for high-energy polarimetry such as NASA’s COSI satellite, and have strong synergies with VHE gamma-ray instruments, that we are using to extend this analysis to the gamma-ray regime. This synergy is particularly relevant at the moment thanks to the construction of the Cherenkov Telescope Array Observatory (CTAO), that will be the best ground-based gamma-ray observatory for the next 3 decades.

About the talk

High-energy blazar emission through multi-wavelength polarimetry and synergies with VHE observations
Dr. Jorge Otero Santos
INFN, Padova, Italy
Thursday May 28, 2026 - 10:30 GMT+1  (Aula)
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About the speaker

After completing a Bachelor’s degree in Physics at Universidade de Santiago de Compostela, Jorge Otero went on to study a Master’s and PhD in Astrophysics at Universidad de La Laguna and Instituto de Astrofísica de Canarias, respectively, specialising in multi-wavelength and high-energy astrophysics, and gamma rays within the MAGIC Cherenkov telescopes collaboration. His research is focused on the multi-frequency variability of blazars — active galactic nuclei with relativistic jets pointing towards Earth — known for their emission up to gamma-ray energies.

After his PhD, he developed a first postdoctoral period at Instituto de Astrofísica de Andalucía (Granada), continuing this research line as part of the Cherenkov Telescope Array Observatory (CTAO) collaboration — the world’s future most powerful very high-energy gamma-ray telescope — and the LST collaboration, responsible for operating the LST-1 telescope, the first CTAO telescope, currently operational on La Palma. Within the LST collaboration he has acted as coordinator of the extragalactic physics group for the past 2 years. During this time, he also participated in the IXPE collaboration in charge of the design and development of the NASA satellite mission Imaging X-ray Polarimeter Explorer (IXPE) observing polarised emission at high energies in the X-ray band; and in NASA’s Compton Spectrometer and Imager (COSI) mission, aimed at detecting polarised gamma-ray emission for the first time, scheduled for launch in 2027.

Currently, he works as a postdoctoral fellow at the Padova section of Istituto Nazionale di Fisica Nucleare (INFN) in Italy, where he is also one of the coordinators of the extragalactic physics working group of the MAGIC Collaboration. Starting in October, he will start a new postdoctoral stage as a CTAO postdoctoral fellow at the high-energy astrophysics group of the Instituto for Cosmic Ray Research (ICRR) in Kashiwa, Tokyo.

 

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