TY - GEN
T1 - The isotropy problem of Ultra-high energy cosmic rays
T2 - 33rd International Cosmic Rays Conference, ICRC 2013
AU - Kumar, Rahul
AU - Eichler, David
N1 - Publisher Copyright:
© 2013 Sociedade Brasileira de Fisica. All Rights Reserved.
PY - 2013/1/1
Y1 - 2013/1/1
N2 - We show that particle drift may play an important role in the transport of ultra-high energy cosmic rays (UHECRs) and their measured anisotropy, particularly when the transport is anisotropic. Drift and anisotropic diffusion has not been adequately included in previous studies. To fully account for the discreteness of UHECR sources in space and time, the Monte Carlo method is used to randomly place sources in the Galaxy and calculate the anisotropy of UHECR flux, given specific realisations of source distribution. We show that reduction in the rate of cross-field transport reduces the anisotropy. However, if the cross-field transport is very small, drift of UHECRs in the Galactic magnetic field (GMF) becomes the dominant contributor to the anisotropy. Test particle simulations further illustrate the effect of drift and verify our analytical calculation. The surprisingly low anisotropy measured by Auger can be interpreted as intermittency of UHECR sources, without invoking a flat source distribution and/or a high source rate.
AB - We show that particle drift may play an important role in the transport of ultra-high energy cosmic rays (UHECRs) and their measured anisotropy, particularly when the transport is anisotropic. Drift and anisotropic diffusion has not been adequately included in previous studies. To fully account for the discreteness of UHECR sources in space and time, the Monte Carlo method is used to randomly place sources in the Galaxy and calculate the anisotropy of UHECR flux, given specific realisations of source distribution. We show that reduction in the rate of cross-field transport reduces the anisotropy. However, if the cross-field transport is very small, drift of UHECRs in the Galactic magnetic field (GMF) becomes the dominant contributor to the anisotropy. Test particle simulations further illustrate the effect of drift and verify our analytical calculation. The surprisingly low anisotropy measured by Auger can be interpreted as intermittency of UHECR sources, without invoking a flat source distribution and/or a high source rate.
KW - Anisotropy
KW - CRs
KW - UHECRs
UR - http://www.scopus.com/inward/record.url?scp=85052395563&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:85052395563
T3 - Proceedings of the 33rd International Cosmic Rays Conference, ICRC 2013
BT - Proceedings of the 33rd International Cosmic Rays Conference, ICRC 2013
PB - Sociedade Brasileira de Fisica
Y2 - 2 July 2013 through 9 July 2013
ER -