INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy.
Gran Sasso Science Institute (INFN), Viale F. Crispi 6, 60100 L'Aquila, Italy.
Phys Rev Lett. 2015 Sep 18;115(12):121101. doi: 10.1103/PhysRevLett.115.121101. Epub 2015 Sep 15.
The ultrahigh-energy cosmic rays observed on the Earth are most likely accelerated in extra-Galactic sources. For the typical luminosities invoked for such sources, the electric current associated to the flux of cosmic rays that leave them is large. The associated plasma instabilities create magnetic fluctuations that can efficiently scatter particles. We argue that this phenomenon forces cosmic rays to be self-confined in the source proximity for energies E<E_{cut}, where E_{cut}≈10^{7}L_{44}^{2/3} GeV for low background magnetic fields (B_{0}≪nG). For larger values of B_{0}, cosmic rays are confined close to their sources for energies E<E_{cut}≈2×10^{8}λ_{10}L_{44}^{1/4}B_{-10}^{1/2} GeV, where B_{-10} is the field in units of 0.1 nG, λ_{10} is its coherence lengths in units of 10 Mpc, and L_{44} is the source luminosity in units of 10^{44} erg/s.
在地球上观测到的超高能宇宙射线很可能是在银河系外的源中加速的。对于这种源所涉及的典型亮度，与离开它们的宇宙射线通量相关的电流很大。相关的等离子体不稳定性会产生磁涨落，可以有效地散射粒子。我们认为，这种现象迫使宇宙射线在源附近被自约束，对于能量 E<E_{cut}，其中 E_{cut}≈10^{7}L_{44}^{2/3} GeV 对于低背景磁场（B_{0}≪nG）。对于较大的 B_{0}值，宇宙射线在能量 E<E_{cut}≈2×10^{8}λ_{10}L_{44}^{1/4}B_{-10}^{1/2} GeV 下被约束在其源附近，其中 B_{-10}是以 0.1 nG 为单位的场强，λ_{10}是以 10 Mpc 为单位的相干长度，L_{44}是以 10^{44} erg/s 为单位的源亮度。
