The possibility of investigating ultra-high-energy cosmic-ray sources using data on the extragalactic diffuse gamma-ray emission

Abstract

We provide our estimates of the intensity of the gamma-ray emission with an energy near 0.1 TeV generated in intergalactic space in the interactions of cosmic rays with background emissions. We assume that the cosmic-ray sources are point like and that these are active galactic nuclei. The following possible types of sources are considered: remote and powerful ones, at redshifts up to z = 1.1, with a monoenergetic particle spectrum, E = 10 21 eV; the same objects, but with a power-law particle spectrum; and nearby sources at redshifts 0 < z ≤ 0.0092, i.e., at distances no larger than 50 Mpc also with a power-law particle spectrum. The contribution of cosmic rays to the extragalactic diffuse gamma-ray background at an energy of 0.1 TeV has been found to depend on the type of sources or, more specifically, the contribution ranges from f <<10 −4 to f ≈ 0.1, depending on the source model. We conclude that the data on the extragalactic background gamma-ray emission can be used to determine the characteristics of extragalactic cosmic-ray sources, i.e., their distances and the pattern of the particle energy spectrum.

Study of cosmic ray sources using data on extragalactic diffuse gamma-ray emission

“…However UHECRs generate noticeable diffuse gamma-ray flux that amounts to few tens percent of the flux measured by Fermi LAT (excluding contribution of unresolved gamma-ray sources). The same result was obtained previously in [13] using semi quantitative estimate. We conclude that UHECRs from minor sources can contribute noticeably to extragalactic diffuse gamma-ray emission.…”

Ultra-high energy cosmic rays from supermassive black holes: particle flux on the Earth and extragalactic diffuse emission

“…The cascade gamma-ray emission being the component of IGRB, its intensity should satisfy the condition Iγ (E>50 GeV) < IGRB without blazars (E>50 GeV). (8) Unresolved gamma-ray source contribution to the IGRB to be 72% (based on the error -14% [28]) we obtain in place of (7): IGRB without blazars (E>50 GeV) =3.71•10 -10 (cm -2 s -1 sr -1 ). (9) With this value the condition (8) is satisfied if the injection spectral index is α≤-1.…”

“…( 6) This value includes the emission from individual unresolved gamma-ray sources. Their contribution to the IGRB at energies E>50 GeV equals to 86 (−14,+16)% [28]. Subtracting from the IGRB the unresolved source contribution of 86%, we obtain IGRB without blazars (E>50 GeV) =1.855•10 -10 (cm -2 s -1 sr -1 ).…”

Contribution of Cosmic Rays from Sources with a Monoenergetic Proton Spectrum to the Extragalactic Diffuse Gamma-Ray Emission

“…The mean free paths of particles with such an energy is ∼ 10 Mpc and, as a result, the CR energy is efficiently transferred to the cascade and, consequently, to the gamma-ray emission. A detailed analysis is provided in (Uryson 2017b). It follows from (7) and (8) that stronger evolution of sources (as in radio galaxies) leads to an increase in the intensity of the cascade gamma-ray emission.…”