Date of Award

7-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace, Physics, and Space Sciences

First Advisor

Ming Zhang

Second Advisor

Gnana Bhaskar Tenali

Third Advisor

Manasvi Lingam

Fourth Advisor

Sofiane Bourouaine

Abstract

Several ground-based cosmic ray (CR) air shower experiments have produced sky maps of intensity anisotropy in the energy range from 1 TeV to a few hundred TeVs with very high statistics and angular resolution. These measurements provide opportunities to study CR sources and propagation in the interstellar medium (ISM). Such studies present two major difficulties. Firstly, CRs are deflected by the heliospheric magnetic field on the last stretch of their journey to Earth. Secondly, measurements at different latitudes are difficult to compare, leading to uncertainties in latitudinal variations on the order of the observed anisotropy. Experiments usually assume latitudinal variations are negligible, and normalize every isolatitudinal band to 1. This results in ``relative intensity" maps, which may not accurately represent the true anisotropy. We utilize a method based on Liouville's theorem to solve these two issues. We map the 4 TeV Tibet ASγ data to the ISM, and study CR propagation there at the present epoch, and in a volume near the solar system. The propagation of CRs is governed by a Fokker-Planck equation. We have noted various issues with common solutions, and produced our own. The gradient and time-derivative of the relative intensity, which are not know a priori, are expanded as a power series of pitch-angle cosine, with expansion coefficients left as fitting parameters. From our model fit, we find that the pristine interstellar magnetic field intensity decreases in the direction of the northern Galactic halo. Moreover, we provide an estimate of the relative intensity gradient parallel to the magnetic field, and a constraint on the time derivative of the relative intensity. Using the ARGO-YBJ data for 7 energy bands from 0.98 TeV to 29.1 TeV, we find the energy dependence of our model parameters: These tend to decay with energy. Then, we compare our results for northern hemisphere maps to a fit to a southern hemisphere map of 13 TeV CRs provided by the IceCube experiment, and show that southern hemisphere fields of view (FoVs) lack important anisotropy features present in northern maps. This underlines the need for a full-sky map in anisotropy analyses.

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