Palestrante
Descrição
Observation of Ultra-High Energy Cosmic Rays (UHECR) and very energetic Gamma-Rays play a fundamental role in the contemporary scenario of multi-messenger astronomy. Lacking the possibility of direct detection of such particles, mostly because of the low flux, current observatories dedicate instruments for indirect observations based on Extensive Air Showers (EAS). EAS are complex particle cascades induced by the interaction of the primary particle with the atmosphere. Two contributions to this scenario are presented related to the parametrization of EAS observables. In the context of UHECR, the distribution of depths at which a cascade reaches its maximum number of particles ($X_{max}$), which can be detected by employing fluorescence detectors (1), is studied in terms of two existing functional forms - Exponentially Modified Gaussian (EMG) and Generalized Gumbel (GMB) - and one new function is proposed - Log-Normal (LN). A very large number of showers were simulated for four distinct primary masses - proton, carbon, silicon and iron - with energies ranging from $10^{17}$ eV to $10^{20}$ eV and three hadronic interaction models: EPOS-LHC, QGSJetII.04, and Sibyll2.3c. The function that best describes the $X_{max}$ distributions is studied in terms of the Akaike information theory and it is shown that the commonly used EMG distribution provides the worst description in all cases, while the GMB is, in general, the best choice for describing $X_{max}$ distributions. The LN distribution is also shown to be a good choice in the proton case. A parametrization of the three functional forms is provided as a function of primary mass and energy for each functional form and hadronic interaction model. Gamma rays in the GeV to TeV range, on the other hand, are typically detected by collecting Cherenkov photons produced by the passage of relativistic shower particles in the atmosphere. (2) While the Cherenkov radiation is well understood from a theoretical point of view, from a phenomenological perspective there is no known parametrization of the angular distributions of these photons that is able to reproduce together both small and large angle distributions in air showers. (3) These angular distributions are studied and a theoretically motivated parametrization of these distributions is provided as a function of shower age in terms of a single parameter.
Referências
1 BELLIDO, J. et al. Depth of maximum of air-shower profiles at the Pierre Auger Observatory: measurements above $10^{17.2}$ V and composition implications. In: INTERNATIONAL COSMIC RAY CONFERENCE, ICRC, 35., 2017, Busan. Proceedings... Trieste : Scuola Internazionale Superiore di Studi Avanzati - SISSA. v. 301, p. 506-1-506-7, 2017. doi: 10.22323/1.301.0506.
2 HILLAS, A. M.; PATTERSON, J. R. Characteristics and brightness of Cerenkov shower images for gamma ray astronomy near 1 TeV. Journal of Physics G, v. 16, n. 8, p. 1271-1281, 1990.
3 NERLING, F. et al. Universality of electron distributions in high-energy air showers: description of Cherenkov light production. Astroparticle Physics, v. 24, n. 6, p. 421-437, 2006.
| Apresentação do trabalho acadêmico para o público geral | Não |
|---|---|
| Subárea | Astronomia, Astrofísica e Cosmologia |
