Cosmic ray tracers from gas-rich active galaxies
Final Report Abstract
The identification of the origin of cosmic rays (CRs) is one of the most challenging and most interesting questions in the field of astrophysics today. Neutral cosmic ray secondaries produced at the CR production site are well-suited for studies of the origin of cosmic rays, in particular when different wavelengths are combined to search for correlated signals. In this project, high-energy-signatures from cosmic ray interactions in active galaxies were investigated. Active galaxies are one of the few candidates that fulfill the mandatory criteria for the acceleration of cosmic rays up to the highest energies, i.e. up to E ~ 10^21 eV. This makes them one of the prime candidates to be responsible for the recently detected signal of astrophysical high-energy neutrinos by the IceCube experiment. Here, different AGN sub-classes were investigated with respect to their potential contribution to the observed diffuse neutrino flux as well as their potential to become visible as point sources. The most promising point source candidate is the nearby Galaxy Centaurus A. A flattening of the gamma-ray spectrum is detected, and thus, the expected flux at higher energies does not decrease significantly. The expected flux is about a factor of 6 below current limits from IceCube and ANTARES and is difficult to detect. KM3NeT and IceCube-Gen2, on the other hand, reach sensitivities about a factor of a few below the expected flux and would be able to detect Centaurus A. The measured diffuse flux is also well-explained by the sub-class of FR-I galaxies to which Cen A belongs. FR-II galaxies, which are more powerful but less frequent, cannot explain the signal. An alternative scenario would be hadronic interactions in blazars. Future measurements in combination with theoretical calculations of the signal expectations from different source environments in active galaxies will lead the way to identifying the sources of high-energy neutrino emission and by that pin-point the .sources of ultra high-energy cosmic rays. The central and most important development in astroparticle physics was the publication of the detection of a diffuse signal of astrophysical high-energy neutrinos, with a first official announcement in May 2013. We therefore changed the course of this project slightly to investigate which sources can be responsible for such a signal, rather than using IceCube limits. This meant that a much more focused investigation was possible, as both spectral shape and intensity can be estimated from the signal. The main change in the work program was to focus on proton-proton interactions rather than including a detailed investigation of proton-photon interactions. Jun 07, 2013: interview WDR 5 Radio - Leonardo, on potential neutrino sources detected with IceCube (www.wdr5.de/sendungen/leonardo/s/d/07.06.2013-16.05/b/mission-eiswuerfel-reloaded-130607.html) Dec 21, 2011: interview WDR 5 Radio - Leonardo, on IceCube completion and potential physics with IceCube (www.wdr5.de/sendungen/leonardo/s/d/21.12.2011-16.05/b/zur-neutrino-jagd-am-suedpol.html)
Publications
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Limits on the source properties of FR-I galaxies from high-energy neutrino and gamma observations, Astrop.Phys. 48:30 (2013)
I . Saba, J. Becker Tjus, F. Balzen
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Neutrinos from astrophysical sources, Acta Physica Pol. B Proc. Suppl., Vol. 6 (2013)
I. Saba, .J. Becker Tjus, F. Balzen
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Calculating column densities for FR-I and FR-II galaxies. (2014) Proceedings, pp.483-486, Conference: C14-03-15.1
S.M. Saba, J. Becker Tjus,B. Eichmann
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High-energy neutrinos from radio galaxies, PRD 89(12):123005 (2014)
J. Becker Tjus, B. Eichmann, F. Balzen, A. Kheirandish, S.M. Saba
