Probing the environments surrounding ultrahigh energy cosmic ray accelerators and their implications for astrophysical neutrinos
Marco Stein Muzio, Glennys R. Farrar, M. Unger
Abstract
We explore inferences on ultrahigh energy cosmic ray (UHECR) source environments---constrained by the spectrum and composition of UHECRs and nonobservation of extremely high energy neutrinos---and their implications for the observed high energy astrophysical neutrino spectrum. We find acceleration mechanisms producing power-law cosmic ray (CR) spectra $\ensuremath{\propto}{E}^{\ensuremath{-}2}$ are compatible with UHECR data, if CRs at high rigidities are in the quasiballistic diffusion regime as they escape their source environment. Both gas-dominated and photon-dominated source environments are able to account for UHECR observations, however photon-dominated sources give a better fit. Additionally, gas-dominated sources are in tension with current neutrino constraints. Accurate measurement of the neutrino flux at $\ensuremath{\sim}10\text{ }\text{ }\mathrm{PeV}$ will provide crucial information on the viability of gas-dominated sources, as well as whether diffusive shock acceleration is consistent with UHECR observations. We also show that UHECR sources are able to give a good fit to the high energy portion of the astrophysical neutrino spectrum, above $\ensuremath{\sim}\mathrm{PeV}$. This common origin of UHECRs and high energy astrophysical neutrinos is natural if air shower data is interpreted with the sibyll2.3c hadronic interaction model, which gives the best-fit to UHECRs and astrophysical neutrinos in the same part of parameter space, but not for epos-lhc.