CONSTRAINING THE EMISSIVITY OF ULTRAHIGH ENERGY COSMIC RAYS IN THE DISTANT UNIVERSE WITH THE DIFFUSE GAMMA-RAY EMISSION

Journal Article · Mon Aug 01 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/736/2/112· OSTI ID:21578249

Xiangyu, Wang; Ruoyu, Liu ^[1]; Aharonian, Felix ^[2]

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1. Department of Astronomy, Nanjing University, Nanjing 210093 (China)
2. Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg (Germany)

Ultrahigh cosmic rays (UHECRs) with energies {approx}> 10{sup 19} eV emitted at cosmological distances will be attenuated by cosmic microwave and infrared background radiation through photohadronic processes. Lower energy extragalactic cosmic rays ({approx}10{sup 18}-10{sup 19} eV) can only travel a linear distance smaller than {approx}Gpc in a Hubble time due to the diffusion if the extragalactic magnetic fields are as strong as nano-Gauss. These prevent us from directly observing most of the UHECRs in the universe, and thus the observed UHECR intensity reflects only the emissivity in the nearby universe within hundreds of Mpc. However, UHECRs in the distant universe, through interactions with the cosmic background photons, produce UHE electrons and gamma rays that in turn initiate electromagnetic cascades on cosmic background photons. This secondary cascade radiation forms part of the extragalactic diffuse GeV-TeV gamma-ray radiation and, unlike the original UHECRs, is observable. Motivated by new measurements of extragalactic diffuse gamma-ray background radiation by Fermi/Large Area Telescope, we obtained upper limit placed on the UHECR emissivity in the distant universe by requiring that the cascade radiation they produce not exceed the observed levels. By comparison with the gamma-ray emissivity of candidate UHECR sources (such as gamma-ray bursts (GRBs) and active galactic nuclei) at high redshifts, we find that the obtained upper limit for a flat proton spectrum is {approx_equal} 10{sup 1.5} times larger than the gamma-ray emissivity in GRBs and {approx_equal} 10 times smaller than the gamma-ray emissivity in BL Lac objects. In the case of iron nuclei composition, the derived upper limit of UHECR emissivity is a factor of 3-5 times higher. Robust upper limit on the cosmogenic neutrino flux is further obtained, which is marginally reachable by the Icecube detector and the next-generation detector JEM-EUSO.

• OSTI ID: 21578249
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 736; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC GAMMA BURSTS
COSMIC RADIATION
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
EMISSIVITY
FERMIONS
GAMMA RADIATION
IONIZING RADIATIONS
LEPTONS
MASSLESS PARTICLES
MICROWAVE RADIATION
NEUTRINOS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PRIMARY COSMIC RADIATION
RADIATIONS
RELICT RADIATION
SURFACE PROPERTIES
UNIVERSE