Constraint on electromagnetic acceleration of highest energy cosmic rays

Area of Science:

• Astrophysics
• Particle Physics
• Cosmic Ray Physics

Background:

• Ultrahigh-energy cosmic rays (UHECRs) are enigmatic particles with energies exceeding 10^18 eV.
• The origin and acceleration mechanisms of UHECRs remain a significant puzzle in astrophysics.
• Constraints on UHECR sources are derived from particle energetics, confinement, and radiative losses.

Purpose of the Study:

• To investigate the viability of compact cosmic accelerators as sources of UHECRs.
• To test the hypothesis that astrophysical objects with strong magnetic fields can accelerate particles to extreme energies.
• To identify potential sources capable of producing the highest energy cosmic ray events.

Main Methods:

• Analysis of the energetics of electromagnetic acceleration for charged particles.
• Modeling particle confinement within acceleration sites and radiative energy losses in magnetic fields.
• Comparing theoretical constraints with observational data of UHECR events, particularly those around 3 x 10^20 eV.

Main Results:

• The detection of UHECR events around 3 x 10^20 eV is inconsistent with compact accelerators possessing high magnetic fields.
• Spinning neutron stars and active galactic nuclei (AGNs) are ruled out as primary UHECR sources under these conditions.
• Galaxy clusters, AGN radio lobes, and gamma-ray burst blast waves remain plausible, albeit weakly supported, candidates for UHECR acceleration.

Conclusions:

• Compact, high-magnetic-field cosmic accelerators are unlikely sources of the most energetic cosmic rays observed.
• Future data from experiments like the Auger observatory will be crucial in determining if conventional physics can explain UHECR origins or if new physics is required.
• The study narrows down the possibilities for UHECR acceleration sites, guiding future research directions.