Measurement of the radial diffusion coefficient of galactic cosmic rays near the Earth by the GRAPES-3 experiment

Radio halos and relics from extended cosmic-ray ion distributions with strong diffusion in galaxy clusters

“…This large diffusion coefficient, inferred on large scales in the ICM, corresponds to a coherence length of order a kpc and is significantly higher than found in galaxies, but is consistent with the observed scaling of D with system size. Indeed, diffusion measurements from small to large scales include D ≃ 10 23 cm 2 s −1 around 10 GeV in the solar wind (Chhiber et al 2017;Kojima et al 2018); D ≃ 10 26.5 E 0.2-0.6 10 cm 2 s −1 in molecular clouds (Ohira et al 2011); D ≃ 10 28 E 0.9 100 cm 2 s −1 in the central few pc of the Milky-Way (Chernyakova et al 2011); D 2 × 10 27 cm 2 s −1 at ∼ 100 GeV perpendicular to galactic disks (Dahlem et al 1995); D ≃ 10 27 -10 28 cm 2 s −1 between 1 GeV and 1 TeV in starburst galaxies (Krumholz et al 2020); D ≃ 10 28.5 E 0.5 100 cm 2 s −1 in other galaxies (Heesen et al 2016); D ≃ 10 28.5 E 0.5 100 cm 2 s −1 for the Milky Way (e.g., Krumholz et al 2020); D ≃ 10 30 E 0.48±0.02 100 cm 2 s −1 near the edges of the ∼ 10 kpc Fermi bubbles (Keshet & Gurwich 2017); D 10 30 cm 2 s −1 around 100 GeV as a possible explanation for uniform, 20 kpc radio bubbles in the IGM (e.g., Mathews & Guo 2011); and D ≃ 10 30 cm 2 s −1 inferred in MHs for an AGN-driven hadronic model (Ignesti et al 2020). Moreover, a combination of somewhat weaker diffusion and additional mixing processes, such as spiral flows in MHs and merger dynamics in GHs, may also explain the data.…”

Solar wind velocity dependence of the flow of galactic cosmic rays perpendicular to the ecliptic plane on the polarity of the interplanetary space magnetic field

“…We also have obtained the radial density gradient of cosmic rays near Earth from the amplitudes of phase reversal of cosmic ray sidereal anisotropies on the polarity of the IMF [2]. From these quantities and the one dimensional diffusion convection equation that can explain the propagation of cosmic rays in the heliosphere, we have derived the diffusion coefficient of the galactic cosmic rays in the IMF plasma [4]. Then, we have explained the role of the variation of the solar wind velocity on the propagation process of the cosmic rays in the Heliosphere.…”

“…We have continuously observed muon intensities from 2000 to the present using the multidirectional muon telescope GRAPES-3 in Ooty, south India. The radial diffusion coefficient and the mean free path of propagation of the Galactic cosmic rays (GCR) in the heliosphere have been derived from the density gradient obtained from the flow perpendicular to the ecliptic plane of GCR, which depends on the polarity of the interplanetary magnetic field (IMF) (Kojima et al, 2018). In this study, we used the data set for the years 2000-2021, covering about 8,000 days and divided into 13 groups by the solar wind velocity to examine the relationship between the amplitude and phase of the flow as mentioned above of each group with the average solar wind velocity on the corresponding group.…”

Dependence of solar diurnal variation on solar wind speed

“…We have continuously observed muon intensities from 2000 to the present using the GRAPES-3 multi-directional muon telescope in Ooty, South India. The radial diffusion coefficient and mean free path of the propagation of Galactic cosmic rays (GCR) in the heliosphere have been derived from the regression coefficients of cosmic-ray intensity and solar wind velocity variations [6]. In the present study, we used the same dataset for the years 2000-2021, covering about 5000 days and divided into 26 groups by the solar wind speed to examine the relationship of the amplitude and phase of solar diurnal variation of each group with the average solar wind speed on the corresponding group.…”