Ursprung der Fermi Bubbles durch Multi-Wellenlängen und Multi-Botenteilchen Beobachtungen
Zusammenfassung der Projektergebnisse
The Fermi bubbles are two large lobes of gamma-ray emission above and below the center of our Galaxy, which were discovered in the Fermi gamma-ray space telescope data in 2010. The origin of the of the Fermi bubbles is yet unclear. Such lobes can be produced by the past activity of the supermassive black hole (SMBH) at the center of our Galaxy or by supernova explosions near the Galactic center either by a single powerful burst event or by a series of supernova explosions or jet emissions from the SMBH spread over millions or, possibly, billions of years. Earlier analysis of the Fermi LAT data at the base of the Fermi bubbles has shown that the emission in this region is brighter and extends to higher energies than the gamma-ray emission from the Fermi bubbles at high latitudes. This property of the gamma-ray emission at the base of the Fermi bubbles opened up a possibility for a detection at higher energies with groundbased Cherenkov telescopes, such as the H.E.S.S. telescopes. Provided that the Fermi telescope has little statistics at high energies, a detection with Cherenkov telescopes (which have a much larger collecting area than the space-based Fermi telescope) would be an important step to study the spectrum and morphology of the Fermi bubbles near the Galactic center with the very-high-energy gamma rays, which may hold the key to the solution of the Fermi bubbles’ origin problem. The main goals of the project have been to perform a detailed analysis of the currently available Fermi -LAT data at the base of the Fermi bubbles and to search for the excess gamma-ray emission in H.E.S.S. Cherenkov telescopes data in that region. We have analyzed 14 years of the Fermi telescope data (from the start of the mission in 2008 till 2022) and 6 years of H.E.S.S. data (which include a dedicated survey of the area near the Galactic center performed by the H.E.S.S. collaboration between 2014 and 2020). We confirm with the new data analysis the earlier results based on the Fermi telescope data that revealed a hard and bright emission at the base of the Fermi bubbles up to about 1 TeV energies. The existence of this emission requires a source of CR electrons or protons, which have been active in the past 100 thousand years. A series of bursts which happen every 100 thousand years, e.g., mini-jets from the SMBH at the Galactic center or a quasi-continuous source of CR coming from bursts with shorter timescale, e.g., from supernova explosions happening on average every thousand years, can explain both the bright emission at the base of the Fermi bubbles and the emission inside the Fermi bubbles further away from the Galactic plane. Although a single powerful emission from the SMBH or from a starburst activity near the GC about 1 million years ago can explain the high-latitude gamma-ray emission in the Fermi bubbles, it cannot account for the bright emission at the base of the Fermi bubbles (the corresponding CRs would diffuse away from the Galactic plane). Such a powerful burst would also be expected to produce a strong shock at the edge of the Fermi bubbles (which is not observed) as well as high levels of ionization (which can be detected in Oxygen lines, but it is also not observed). As a result, the quasistationary scenario of creation of the Fermi bubbles by a series of mini-jets from SMBH or supernova explosions in the vicinity of the Galactic center is preferred compared to a single powerful burst scenario both by the high energy gamma-ray data observations with Fermi and H.E.S.S. telescopes, which has been the main subject of this proposal, and by multiwavelength observations.
Projektbezogene Publikationen (Auswahl)
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Search for TeV emission from the Fermi Bubbles at low Galactic latitudes with H.E.S.S. inner Galaxy survey observations, Proceedings of 37th International Cosmic Ray Conference PoS(ICRC2021), Vol. 395 (2021)
E. Moulin, A. Montanari, D. Malyshev, Dm. Malyshev
