Description du sujet de thèse

The origin of cosmic rays is one of the great unsolved mysteries in our understanding of the Universe. The main challenge lies in the fact that, being charged, these particles are deflected on their way from their natural accelerator to the Earth. However, there is an indirect way of studying acceleration sites: wherever a cosmic ray is accelerated to high energy, it inevitably interacts with its surroundings, producing photons and neutrinos. These by-products travel along geodesics, making it possible to directly identify particle acceleration sites in the Universe. While observations of photons are often ambiguous, neutrinos represent a truly irrefutable signature of the acceleration of cosmic rays in astrophysical objects. This indirect window on natural particle accelerators has finally been opened thanks to the development of neutrino astronomy and the first multi-messenger observation campaigns. We have now accumulated several indications (at the level of 3 to 4 sigmas) of neutrino emission from active galactic nuclei, the observable manifestation of accretion onto supermassive black holes, but we still lack unambiguous detections beyond 5 sigmas.
The next-generation gamma-ray and neutrino telescopes are already under construction: they will considerably improve our observational capabilities, allowing us to fully enter the multi-messenger era.
The PhD student's activities will include :
* Development of multi-wavelength and multi-messenger data fitting algorithms
* Analysis of TeV data from CTAO telescopes
* Collaborative software development within Gammapy
* Numerical modelling of radiative emission
* Collaborative work within the CTAO Collaboration
* Participation in research trips, workshops and conferences
* Publication of research results.

Contexte de travail

The APC laboratory is a leading centre for multi-messenger astronomy located in Paris, France. The successful candidate will have the opportunity to collaborate with teams working on neutrinos (KM3NET), X-rays (SVOM), gravitational waves (VIRGO), as well as with groups in theory, cosmology and particle physics. There will also be opportunities for collaboration with other gamma-ray research groups in Paris, including the Observatoire de Paris.
The PhD student will join the COCOA-NuGETs research project, funded by
the ANR (COnstraints on COsmic-ray Acceleration by Neutrino and Gamma-ray
observations of Extragalactic TargetS, see https://anr.fr/fr/rechercher-sur-
anrfr/?q=COCOA+NuGETs&id=1817&L=0), which builds on these first multi-messenger results and prepares the early science of the CTAO observatory (Cherenkov Telescope Array Observatory). This thesis focuses on the development and application of innovative analysis methodologies exploiting the synergy of gamma-ray and neutrino observations to locate cosmic ray acceleration sites in the Universe. The PhD student will work on two complementary aspects: on the one hand, he/she will contribute to the implementation of advanced multi-wavelength and
multi-messenger fitting algorithms in the Gammapy software, enabling joint analysis and coherent modelling of gamma-ray and neutrino data. This will provide a robust basis for interpreting the observations within a unified astrophysical framework, and will produce statistically sound constraints on the parameters of the models, and hence on the physical properties of the cosmic ray accelerators; secondly, he/she will analyse the first data provided by the CTAO North antenna in order to identify and characterise the neutrino emitting black hole systems by applying the tools developed in the first part.

Contraintes et risques

No particular constraints or risks.
Short periods of travel in France and abroad may be necessary.