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The Auger observatory has observed a possible correlation between UltrahighEnergy Cosmic Rays (UHECRs) above 57 EeV and nearby candidate Active GalacticNuclei (AGN) from the Veron-Cetty Veron catalog (VCV). In this paper we reporton Chandra X-ray observations of 10 unconfirmed VCV AGN-candidates and luminousIR galaxies correlating with the first set of Auger UHECRs, to determinewhether or not they have active nuclei. The X-ray data, when combined withoptical luminosities, show that in fact none of the 10 galaxies have asignificant AGN component; if there is any nuclear activity at all, it is weakrather than obscured. This reduces the number of UHECRs in the original Augerdataset possibly correlating with AGNs from 20 of 27 down to 14 of 27. We alsoused Chandra to measure the X-ray luminosity of ESO 139-G12, an AGN whichcorrelates with 2 of the Auger UHECRs, to obtain the first estimate of itsbolometric luminosity; this completes the determination of the bolometricluminosities of all correlating AGNs. Taking our results into account, only oneof the 27 UHECRs in the original Auger data-release is correlated on afew-degree angular scale with an identified AGN that is powerful enough in itssteady-state to accelerate protons to the observed energies, according toconventional acceleration mechanisms. Intriguingly, approximately 60% of theUHECRs with $|b|>10^\circ$ do correlate with genuine AGNs, but these are tooweak to meet the acceleration criterion for protons; this may be an indicationthat AGNs experience transient high-luminosity states which can accelerateUHECRs. To determine the source(s) and composition of UHECRs throughstatistical correlation studies requires reliable, complete and uniformcatalogs of identified AGNs; our a posteriori inspection of ambiguous sourcecandidates underscores the inadequacies of the VCV catalog in this respect.

Chandra observations of AGN-candidates correlated with Auger UHECRs