Time Variation in the TeV Cosmic Ray Anisotropy with IceCube and Energy Dependence of the Solar Dipole

TL;DR

This paper investigates the time variation of TeV cosmic ray anisotropy using IceCube data, exploring effects like solar activity and Earth's motion, and provides preliminary measurements of the cosmic-ray spectral index.

Contribution

It presents a preliminary analysis of time-dependent cosmic ray anisotropy and the energy dependence of the solar dipole using IceCube data, including the first measurement of the spectral index variation.

Findings

Detection of the Compton-Getting Effect in IceCube data

Evidence of time variation in cosmic ray anisotropy

Preliminary measurement of the cosmic-ray spectral index below the knee

Abstract

There is an observed anisotropy in the arrival direction distribution of cosmic rays in the TeV-PeV regime with variations on the scale of one part in a thousand. While the origin of this anisotropy is an open question, a possible factor is cosmic-ray interactions with interstellar and heliospheric magnetic fields. These magnetic fields may change over time - for example, due to changes in solar activity throughout its 11-year solar cycle. The cosmic-ray anisotropy can reflect these time-dependent magnetic fields. In addition to these speculative sources, there are several known sources of time variation in this anisotropy, such as the Compton-Getting Effect from the Earth's orbital motion. We discuss a preliminary study with limited statistics of time variation undertaken by the IceCube Neutrino Observatory, including a measurement of the Compton-Getting Effect as well as a general, model-independent search for other time variations. Further, we use the Compton-Getting Effect to present a preliminary measurement of the cosmic-ray spectral index as a function of energy below the knee.