The nature of high-energy gamma-ray emission from Star-Forming Galaxies is of utmost importance for understanding both the origin of Cosmic Rays and the high-energy processes that shape galaxy formation. Observations from the gamma-ray telescope Fermi-LAT have detected gamma-ray emission from a handful of nearby Star-Forming Galaxies. Interestingly, observations of the Small Magellanic Cloud show evidence for a spectral cutoff at energies of approximately 10 GeV. This has raised the question as to whether some Star-Forming Galaxies are unable to contain their Cosmic Ray population. Using the Fermitools to analyse the gamma-ray emission from a selection of bright nearby Star-Forming Galaxies, this study intends to explore the possibility of finding further evidence for exponential cutoffs in the gamma-ray spectrum of Star-Forming Galaxies. The shape of the combined spectrum of the 49 galaxies in the sample was determined using least-square fitting of a single power law, a broken power law and a power law with an exponential cutoff. No evidence of an exponentialcutoff was found and the shape of the spectrum was best described by a broken power law with indices Γ1 = -2.48 ± 0.05 and Γ2 = -0.88 ± 0.09. This is in poor agreement with previous observations, which favour a simple power law with an index in the range -2.2 to -2.4. Interestingly, the single power law, while disfavoured over the broken power law at ~7σ, was best fit with the index Γ = -2.35 ± 0.06, which is surprisingly well in agreement with previous observations. The discrepancy between the results presented here and those found in the literature is interpreted as due to insufficient treatment of background fluctuations and the possible existence of bright sources at the unverified blank sky locations used for modelling the background.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-199100 |
| Date | January 2021 |
| Creators | Svenborn, Oskar |
| Publisher | Stockholms universitet, Fysikum |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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