Beitrag Aktiver Galaxienkerne zur extragalaktischen Neutrinohintergrundstrahlung
Zusammenfassung der Projektergebnisse
The origin of cosmic-rays is still under great debate. After the recent discovery by the AUGER experiment on a possible coincidence of the ultrahigh energy events with some active galactic nuclei (AGN) in the super-galactic plane the class of AGN is one promising candidate. Because of the cosmological distance of these sources, information about the direction of cosmic rays are lost due to magnetic fields. Thus, high energy photons or weak interacting particles like neutrinos are needed to learn more about the origin of high and ultrahigh energy cosmic rays. The new generation of neutrino telescopes like IceCube will be able to test theoretical predictions for the extragalactic Neutrinobackground. It is therefore one of the key subjects to learn about the production mechanisms in cosmic accelerators. In this project the topic of high energy neutrino emission from AGN and Starburst Galaxies has been addressed. In the first part the total neutrino emission from blazars and BL Lacs which are subclasses of AGN has been studied by modeling their contribution to the extragalactic gamma-ray background detected by the EGRET gamma-ray satelite. For the first time the effect of the Compton-pair cascade which develops when the photons travel from the gamma-ray source to earth has been taken into account using an existing model by the applicant. Once the diffuse gamma-ray emission from AGN was calculated the neutrino emission was estimated assuming that the two AGN classes are purely hadronic. The results were able to confirm already published calculations on the neutrino flux from blazars. To give a better estimate possible other contribution to the extragalactic gamma-ray background have been calculated. As a result the extended jet emission from Fanaroff-Riley Galaxies is only 1% and can be ignored, while the gamma-ray emission from Starburst Galaxies (or ultra-luminous infrared galaxies) is still uncertain. Therefore in the second part of the project the gamma-ray and neutrino emission from Starburst Galaxies has been studied in greater detail. A model has been developed including detailed calculation for the interaction processes between cosmic-rays and the interstellar medium. For the first time the total gamma-ray and neutrino flux has been normalized directly to the far-infrared flux of all galaxies, already calculated in an existing model by the applicant. The surprising result was a gamma-ray flux which is about an order of magnitude higher than former calculations. The problem is that the calculation could overestimate the real flux, since the very dense and extreme starforming regions in Starburst Galaxies are not easily average for a whole population of galaxies. For the future the applicant plans to include energy losses and more details, so that gamma-ray and neutrino spectra of individual galaxies can be calculated. This study will lead to a deeper insight into the average properties of the population of Starburst Galaxies.
Projektbezogene Publikationen (Auswahl)
- Extragalactic photon background above Ge V energies: HBL or dark matter? . "The Relativistic Astrophysics and Cosmology - Einstein's Legacy - meeting". ESO Astrophysics Symposia, 2006
Mannheim, K., Elsässer, D. & Kneiske, T.M.
- Kiloparsec-scale jets in FRI radio galaxies and the gamma-ray background. ApJ, 637, 693 (2006)
L. Stawarz, T.M. Kneiske & J. Kataoka
- Direct and reprocessed gamma-ray emission of kpc-scale jets in FR I radio galaxies. AIPC, 921, 363 (2007)
L. Stawarz, T.M. Kneiske & J. Kataoka
- Gamma-ray background: a review. FRASCATI workshop 2007, Vulcano, Italy
- Gamma-ray Background: a review. FRASCATI workshop 2007, Vulcano, Italy. Chinese Journal of Astronomy &: Astrophysics
T.M. Kneiske
- BL Lac contribution to the extragalactic Gamma-Ray Background. A&A, 479, 41 (2008)
T.M. Kneiske & K. Mannheim
- Can the extragalactic_gamma-ray background be explained by AGN ? AIP conference proceeding of "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008"
T.M. Kneiske, K. Mannheim, L. Stawarz & J. Kataoka
