Constraints on the Acceleration of Ultra–High‐Energy Cosmic Rays in Accretion‐induced Collapse Pulsars

(Abridged) We have recently proposed that the ultra-high energy cosmic rays(UHECRs) observed above the GZK limit could be mostly protons accelerated inreconnection sites just above the magnetosphere of newborn millisecond pulsarsoriginated by accretion induced collapse (AIC-pulsars). Although the expectedrate of AIC sources in our own Galaxy is very small, our estimates have shownthat the observed total flux of UHECRs could be obtained from the integratedcontribution from AIC-pulsars of the whole distribution of galaxies locatedwithin a distance which is unaffected by the GZK cutoff ($\sim 50 $ Mpc). Wepresently examine the potential acceleration mechanisms in the magneticreconnection site and find that first-order Fermi acceleration cannot providesufficient efficiency (due to synchrotron losses). This leaves the one-shotacceleration via an induced electric field within the reconnection region asthe only viable process for UHECR acceleration. We formulate the constraints onboth the magnetic field topology and strength in order to accelerate theparticles and allow them to freely escape from the system. Under fastreconnection, we find that AIC-pulsars with surface B-fields $10^{12} $ G $

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