Magnetars in the Metagalaxy: An Origin for Ultra High Energy Cosmic Rays in the Nearby Universe

I show that the relativistic winds of newly born magnetars (neutron stars with petagauss surface magnetic fields) with initial spin rates close to the centrifugal breakup limit, occurring in all normal galaxies with massive star formation, can provide a source of ultrarelativistic light ions with an E injection spectrum, steepening to E at higher energies, with an upper cutoff at 10 − 10 eV. Interactions with the CMB yield a spectrum at the Earth which compares favorably with the spectrum of Ultra-High Energy Cosmic Rays (UHECR) observed at energies up to a few×1020 eV. The fit to the observations suggests that ∼ 5−10% of the magnetars are born with rotation rates and voltages sufficiently high to allow the acceleration of the UHECR. The form the spectrum incident on the Earth takes depends sensitively on the mechanism and the magnitude of gravitational wave losses during the early spindown of these neutron stars pure electromagnetic spindown (the E injection spectrum) yields a GZK feature (a flattening of the EJ(E) spectrum) below 10 eV, rather than a cutoff, while a moderate GZK cutoff appears if gravitational wave losses are strong enough to steepen the injection spectrum above 10 eV. The flux above 10 eV comes from magnetars in relatively nearby galaxies (D < 50 Mpc.) I outline the probable physics of acceleration of such particles in a magnetar’s wind it is a form of “surf-riding” in the approximately force free fields of the wind. I also show how the high energy particles can escape with small energy losses from the magnetars’ natal supernovae. In particular, I show that the electromagnetic energy emitted by the magnetar “shreds” the supernova envelope in times short enough to allow most of the relativistic energy to escape largely unmimpeded into the surrounding interstellar medium, where it drives a relativistic blast wave that expands to parsec scale before slowing down to nonrelativistic speeds. I also show that since the ions are accelerated in a region where the magnetic field has the structure of a strong electromagnetic wave but propagate at also Department of Physics and Theoretical Astrophysics Center