Speaker
Description
The origin of ultra–high–energy cosmic rays (UHECRs), including the $2.44\times10^{20}$ eV event detected by AMATERAS, remains an open problem in astrophysics. Strong magnetic fields, such as those associated with magnetars, are expected to play an important role both in accelerating particles to ultra–high energies and in shaping the accompanying radiation. In such environments, synchrotron emission from UHE protons can produce high-energy $\gamma$-rays that provide valuable information on the nature of UHECR sources.
We present a fully relativistic description of synchrotron emission from UHE protons in intense magnetic fields, treating both electromagnetic $\gamma$ emission and strong-interaction particle production processes involving pions and $\rho$ mesons. The formulation is based on an exact treatment of proton motion in a magnetic field, allows proton recoil effects to be consistently included, and provides a coherent theoretical framework for describing synchrotron emission in the ultra–high–energy regime.
For UHE protons, the Landau quantum number can reach values as large as $ N \gtrsim 10^{15}$, rendering direct calculations impractical. We overcome this difficulty by identifying a generalized scaling rule for transition probabilities, which allows results for extremely large Landau quantum numbers to be inferred from calculations at much smaller values. Our results provide a reliable theoretical basis for interpreting high-energy radiation from UHECR acceleration sites in strong magnetic fields.
[1] Telescope Array Collaboration, Science 382, 903 (2023).
[2] T. Maruyama et al., Phys. Rev. D in press.