Galactic cosmic rays (GCRs) are affected by solar modulation while they propagate through the heliosphere. The study of the time variation of GCR spectra observed at Earth can shed light on the ...underlying physical processes, specifically diffusion and particle drifts. Recently, the AMS-02 experiment measured with very high accuracy the time variation of the cosmic-ray proton and helium flux between 2011 May and 2017 May in the rigidity range from 1 to 60 GV. In this work, a comprehensive three-dimensional steady-state numerical model is used to solve Parker's transport equation and reproduce the monthly proton fluxes observed by AMS-02. We find that the rigidity slope of the perpendicular mean free path above 4 GV remains constant, while below 4 GV, it increases during solar maximum. Assuming the same mean free paths for helium and protons, the models are able to reproduce the time behavior of the p/He ratio observed by AMS-02. The dependence of the diffusion tensor on the particle mass-to-charge ratio, A/Z, is found to be the main cause of the time dependence of p/He below 3 GV.
Very-high-energy (VHE) gamma-ray astronomy can provide insight in to the origin of cosmic rays. The Cygnus arm of the Galaxy is a well studied region and has been shown to have active sources of ...particle acceleration. VERITAS (Very Energetic Radiation Imaging Telescope Array System) is an array of four 12 meter diameter imaging atmospheric Cherenkov telescopes located at the Fred Lawrence Whipple Observatory in southern Arizona. From 2007 through 2012 VERITAS observed the Cygnus region for nearly 300 hours from 67° to 82° in Galactic longitude and from -1° to 4° in Galactic latitude. The survey and followup observations detected four sources: VER J2031+415, VER J2019+407, VER J2016+317, and VER J2019+368. The Fermi Large Area Telescope (Fermi-LAT) is a satellite gamma-ray telescope operating in the high-energy gamma-ray regime. The emission detected by the Fermi-LAT can provide insight into the nature of these sources and guide targeted followup observations in the region. We have reanalyzed the VERITAS data with updated VERITAS analysis and completed an analysis of over seven years of Fermi-LAT data in the region. We have discovered Fermi-LAT emission associated with VER J2031+415 strengthening its interpretation as a pulsar wind nebula, the SNR nature of VER J2019+407 has been confirmed by this study, and VER J2016+317 has been confirmed to be associated with the pulsar wind nebula CTB 87 rather than with a blazar source located at the same position. The Cygnus region is observed to be a particularly bright region of the Galaxy with both very-high-energy and high-energy gamma-ray experiments. These results motivate continued study of the region with VERITAS, as well as with current and future experiments such as HAWC and CTA.
The Cygnus region is a very active region of our Galaxy with many sources of GeV and TeV gamma-ray emission, such as supernova remnants, pulsar wind nebulae, and massive star clusters. A detailed ...study of the Cygnus region at these energies can give insight into the processes of particle acceleration in astrophysical sources. VERITAS (Very Energetic Radiation Imaging Telescope Array System) is an array of four 12 meter diameter imaging atmospheric Cherenkov telescopes located at the Fred Lawrence Whipple Observatory (FLWO) in southern Arizona. From 2007 through 2012 VERITAS observed the Cygnus region for nearly 300 hours, from 67 to 82 degrees Galactic longitude and from -1 to 4 degrees in Galactic latitude. We have reanalyzed the VERITAS data with updated more sensitive analysis techniques and will be cross correlating that data with the results of an analysis of nearly six years of Fermi-LAT data in the region. Using this cross correlation we can motivate continued observations in this active region of the Galaxy.
Galactic cosmic rays (GCRs) are affected by solar modulation while they propagate through the heliosphere. The study of the time variation of GCR spectra observed at Earth can shed light on the ...underlying physical processes, specifically diffusion and particle drifts. Recently, the AMS-02 experiment measured with very high accuracy the time variation of the cosmic ray proton and helium flux between May 2011 and May 2017 in the rigidity range from 1 to 60 GV. In this work, a comprehensive three-dimensional (3D) steady-state numerical model is used to solve Parker's transport equation and is used to reproduce the monthly proton fluxes observed by AMS-02. We find that the rigidity slope of the perpendicular mean free path above 4 GV remains constant, while below 4 GV it increases during solar maximum. Assuming the same mean free paths for helium and protons, the models are able to reproduce the time behavior of the p/He ratio observed by AMS-02. The dependence of the diffusion tensor on the particle mass-to-charge ratio, A/Z, is found to be the main cause of the time dependence of p/He below 3 GV.
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