Jet Physics Across the Multimessenger Spectrum

• Applicant: Professorin Sara Buson, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443220636

The sources of high-energy cosmic rays remain largely unknown, despite decades of research. Because cosmic rays are deflected by magnetic fields, tracing them back to their origin is challenging. High-energy neutrinos are produced through interactions of cosmic rays with ambient matter or photon fields, resulting in the decay of charged and neutral pions into neutrinos and γ rays, respectively. Unlike cosmic rays, neutrinos travel vast distances without deflection or significant absorption, making them powerful messengers for unraveling the sources of cosmic rays. Among the leading candidates for high-energy neutrino production are active galactic nuclei (AGN), particularly a subclass known as blazars. Blazars are supermassive black holes at the centers of galaxies that launch powerful relativistic jets pointed nearly directly towards Earth. These jets are capable of accelerating particles to extremely high energies, potentially producing both γ rays and neutrinos through hadronic processes. Blazars are the overwhelming population of sources detected at γ rays with the Fermi-LAT. This project aims to leverage the synergy between neutrino observatories and the Fermi-LAT follow-up capabilities, while also leveraging the complementary perspectives offered by IceCube and KM3NeT. It involves the use of both archival data and newly reported high-energy neutrino events detected in real time by IceCube and KM3NeT. The initial phase of the project envisages familiarization with the research field, methodologies, and relevant tools. This is followed by leading contributions to the Fermi-LAT real-time multi-messenger activities. Upon receiving a neutrino alert, a targeted γ-ray analysis is performed to search for emission from both known and transient sources within the neutrino localization region. The electromagnetic properties of candidate astrophysical counterparts to the neutrino are investigated. In the final phase, the project investigates the sample of blazars spatially coincident with high-energy neutrino events, comparing their properties to the general γ-ray blazar population observed by Fermi-LAT. Furthermore, blazar sub-classes, such as BL Lac objects and flat-spectrum radio quasars, will be analyzed separately to investigate potential patterns between their γ-ray and neutrino properties.

• DFG Programme: Research Units
• Subproject of: FOR 5195: Relativistic Jets in Active Galaxies
• Co-Investigator: Professor Dr. Karl Mannheim, Ph.D.