arXiv:1311.0287v1 [astro-ph.HE] 1 Nov 2013 Draft version June 21, 2018 Preprint typeset using L A T E X style emulateapj v. 5/2/11 THE ENERGY PRODUCTION RATE DENSITY OF COSMIC RAYS IN THE LOCAL UNIVERSE IS ∼ 10 44−45 erg Mpc −3 yr −1 AT ALL PARTICLE ENERGIES Boaz Katz 1 , Eli Waxman 2 , Todd Thompson 3,4 , Abraham Loeb 5 Draft version June 21, 2018 ABSTRACT The energy output (per logarithmic interval of particle energies) of Cosmic Rays (CRs) with en- ergies 10 GeV  ε p  100 GeV is ∼ 10 47 erg per solar mass of star−formation, based on the CR production rate in the Milky Way and in starburst galaxies, implying a generation rate of ε 2 p Q ∼ 10 45 erg Mpc −3 yr −1 in the local universe. It is only ∼ 10 times larger than the out- put, ε 2 p Q = 0.5 ± 0.2 × 10 44 erg Mpc −3 yr −1 , of Ultra High Energy CRs (UHECRs) at ener- gies 10 10.5 GeV <ε p < 10 12 GeV (obtained assuming they are mostly protons), which in turn is comparable to the lower limit of ε 2 p Q ≥ 0.5 × 10 44 erg Mpc −3 yr −1 of high energy CRs with 10 6 GeV  ε p  10 8 GeV implied by the saturation of the Waxman-Bahcall bound by the neu- trino excess recently discovered by IceCube. These similarities are consistent with a flat production spectrum, ε 2 p Q ∼ const for CRs at all observed energies. If a flat production spectrum is generated by our galaxy, the observed CR flux in the range 10 6.5 − 10 9.5 GeV, above the ”knee”, is suppressed com- pared to lower energies due to propagation effects rather than acceleration upper limits. As suggested by Parizot and Aublin, the most exciting possibility is that cosmic rays at all energies are emitted from a single type of (unknown) sources, which can not be supernova remnants. Subject headings: cosmic rays 1. INTRODUCTION The origin of the observed Cosmic Rays (CRs) at dif- ferent energies is still unknown (see Blandford & Eichler 1987; Axford 1994; Nagano & Watson 2000; Helder et al. 2012; Lemoine 2013, for reviews). The energy density (per logarithmic particle energy) changes by about 8 or- ders of magnitudes across the observed particle energy range of 10 9 eV − 10 20 eV. The cosmic ray spectrum steepens around ∼ 5 × 10 15 eV (the “knee”) and flattens around 5 × 10 18 eV (the “ankle”). Below the knee the cosmic rays are thought to originate from Galactic super- novae. Above the ankle, the so called Ultra High Energy CRs (UHECRs) are believed to be of extra-Galactic (XG) origin since they cannont be confined by the galactic magnetic field and their measured flux is nearly isotropic. In this letter we use current data to estimate the pro- duction rate of CRs in the local universe at the differ- ent energies and show that CRs of all observed energies may be produced with a universal flat energy produc- tion spectrum ε 2 p d ˙ n/dε p ∼ const. A softer universal production spectrum was suggested by Parizot (2005); Aublin & et al. (2005) with a production rate of low en- ergy CRs which is 1000 times larger than UHECRs. We resolve the differences and show that the softer spectrum 1 Institute for Advanced Study, Einstein Drive, Princeton, New Jersey, 08540, USA 2 Particle Physics & Astrophysics Dept., Weizmann Institute of Science, Rehovot 76100, Israel 3 Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH, 43210, USA 4 Center for Cosmology & Astro-Particle Physics, The Ohio State University, 191 West Woodruff Ave., Columbus, OH, 43210, USA 5 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA found by these authors is due to over(under)estimates of the energy production rates at low(high) energy. 2. ENERGY PRODUCTION RATES AT LOW, INTERMEDIATE AND ULTRA-HIGH ENERGIES If CRs at all energies are produced in galaxies, the observed flux of CRs at low energies is enhanced by sev- eral orders of magnitude due to the confinement of these CRs in our galaxy (Loeb & Waxman 2002) and the CR production spectrum is much harder than the observed spectrum. We next provide estimates for the production of CRs at the different energies for which we have reliable constraints. The estimates are summarized in figure 1. 2.1. UHE energies, ε p ∼ 10 19 − 10 21 eV Consider first the energy production of the highest en- ergy cosmic rays, ε p ∼ 10 19 − 10 21 eV. The distance of the extra-galactic sources of the observed CRs in this range is limited by propagation losses due to the interac- tion with the inter-galactic radiation field. The composi- tion is controversial, with air-shower data from the Fly’s Eye, HiRes and Telescope Array observatories suggest- ing a proton dominated composition (Bird et al. 1993; Abbasi et al. 2010; Sagawa 2011) while the Pierre Auger Observatory suggesting a transition to heavy elements above 10 19 eV (Abraham et al. 2010). Due to this dis- crepancy, and due to the experimental and theoretical uncertainties in the relevant high energy particle inter- action cross sections used for modeling the shape of the air showers, it is impossible to draw a definite conclu- sion regarding composition based on air-shower data at this time. It should be noted that the anisotropy sig- nal measured at high energies, combined with the ab- sence of this signal at low energies, is an indication for a proton dominated composition at the highest energy