General Seminar

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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).

8 April 2025 – TUESDAY

“Novel approaches for understanding the multi-wavelength picture of blazars”

dr Lea Heckmann ( Université Paris Cité, CNRS, Astroparticule et Cosmologie, Paris, France and Max-Planck-Institut für Physik, Garching, Germany)

Abstract:
Blazars are prime objects to investigate in the current multi-messenger era. However, even though they have been studied for decades, we are still deciphering their underlying emission and acceleration mechanisms. In this talk, I will present my research focusing on understanding our brightest TeV blazars in a multi-wavelength (MWL) context. I will focus on two main approaches:
The first approach explores the possibilities opened by the newly available X-ray polarization measurements of blazars by IXPE and combines them with the MWL picture. While the first studies involving data up to the very-high-energy (VHE) gamma-rays cover moderate emission states, a flaring event of Mrk 421 occurred simultaneous to IXPE observations in December 2023. In our study, we manage to explain the observed VHE flare simultaneous to stochastic fluctuations observed in the X-ray polarization and a counter-clockwise hysteresis in the X-rays with highly turbulent electron-ion plasma crossing a shock front inside the blazar jet.
The second approach is exploiting novel analysis methods to investigate blazar data. One the one hand, we use an unsupervised learning technique to identify emission states of blazars in a more unbiased way as done to date. Applied to a long-term MWL data set of the blazar Mrk 501, it allows to identify various high- to low activity-emissions states and finds a distinctive pattern between radio and X-ray fluxes indicating multiple emission zones. On the other hand, we are developing a framework to enable the theoretical interpretation of multi-messenger datasets using the open-source Python package Gammapy. It allows to perform minimization directly on instrumental counts instead of flux points reducing biases coming from the flux point generation, and allowing a simpler treatment of systematics between different instruments and datasets. The goal is to provide an open framework to the community, which can be used to fit any iterable leptonic and hadronic model to MWL datasets.