Predicted High Energy Break in the Isotropic Gamma Ray Spectrum: a Test of Cosmological Origin

Fazio, G. G.; Stecker, F. W.

doi:10.1038/226135a0

Cited by 135 publications

(109 citation statements)

References 5 publications

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“…For example, a cosmic-ray proton with a measured energy of 10 19 eV must have been produced at z < 0:4. This effect is analogous to the Fazio-Stecker relation for gamma rays [69]. As energy losses above 3 10 19 eV are quite severe, the observed UHECR must be produced in the local Universe.…”

Section: Uhecr and Grbsmentioning

confidence: 95%

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

Yüksel

Kistler

2007

Phys. Rev. D

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Gamma-ray bursts, which are among the most violent events in the Universe, are one of the few viable candidates to produce ultra high-energy cosmic rays. Recently, observations have revealed that GRBs generally originate from metal-poor, low-luminosity galaxies and do not directly trace cosmic star formation, as might have been assumed from their association with core-collapse supernovae. Several implications follow from these findings. The redshift distribution of observed GRBs is expected to peak at higher redshift (compared to cosmic star formation), which is supported by the mean redshift of the Swift GRB sample, hzi 3. If GRBs are, in fact, the source of the observed UHECR, then cosmic-ray production would evolve with redshift in a stronger fashion than has been previously suggested. This necessarily leads, through the GZK process, to an enhancement in the flux of cosmogenic neutrinos, providing a near-term approach for testing the gamma-ray burst-cosmic-ray connection with ongoing and proposed UHE neutrino experiments.

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Section: Uhecr and Grbsmentioning

confidence: 95%

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

Yüksel

Kistler

2007

Phys. Rev. D

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“…Still, at very high γ-ray energies the optical depth can be larger than 1, leading to an optically thick Universe. For a given Eγ the redshift at which τγγ = 1 defines the γ-ray horizon (Fazio & Stecker 1970). Figure 5 shows the E − z contours for values of τγγ = 1 − 9 based on the EBL energy density predicted by our model.…”

Section: Absorption Of γ-Ray Spectramentioning

confidence: 99%

Effects of spatial fluctuations in the extragalactic background light on hard gamma-ray spectra

Kudoda¹,

Faltenbacher²

2017

Monthly Notices of the Royal Astronomical Society

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This study investigates the impact of the fluctuations in the extra galactic background light (EBL) on the attenuation of the hard γ-ray spectra of distant blazars. EBL fluctuations occur on the scales up to 100 Mpc and are caused by clustering of galaxies. The EBL photons interact with high energy γ-rays via the electron-positron pair production mechanism: γ + γ ′ → e + + e − . The attenuation of γ-rays depends on their energy and the density of the intervening EBL photon field. Using a simple model for the evolution of the mean EBL photon density, we implement an analytical description of the EBL fluctuations. We find that the amplitudes of the EBL energy density can vary by ±1% as a function of environment. The EBL fluctuations lead to mild alterations of the optical depth or equivalently the transmissivity for γ-rays from distant blazars. Our model predicts maximum changes of ±10% in the γ-ray transmissivity. However, this translates into marginal differences in the power law slopes of currently observed γ-ray spectra. The slopes of deabsorbed γ-ray spectra differ by not more than ±1% if EBL fluctuations are included.

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“…This is due to the fact that photons from distant sources scatter off background photons permeating the Universe, thereby disappearing into electron-positron pairs [1]. It turns out that the corresponding cross section σ(γγ → e + e − ) peaks where the VHE photon energy E and the background photon energy ǫ are related by ǫ ≃ (500 GeV/E) eV.…”

Section: Motivationmentioning

confidence: 99%

A new light boson from MAGIC observations?

Roncadelli¹,

Angelis²,

Mansutti³

2009

Nuclear Physics B - Proceedings Supplements

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Recent detection of blazar 3C279 by MAGIC has confirmed previous indications by H.E.S.S. that the Universe is more transparent to very-high-energy gamma rays than currently thought. This circumstance can be reconciled with observations of nearby blazars provided that photon oscillations into a very light Axion-Like Particle occur in extragalactic magnetic fields. The emerging "DARMA scenario" can be tested in the near future by the satelliteborne Fermi LAT detector as well as by the ground-based Imaging Atmospheric Cherenkov Telescopes H.E.S.S., MAGIC, CANGAROO III, VERITAS and by the Extensive Air Shower arrays ARGO-YBJ and MILAGRO. MOTIVATIONImaging Atmospheric Cherenkov Telescopes (IACTs) are providing us with an impressive amount of information about the Universe in the energy interval 100 GeV − 100 TeV. Observations carried out by these IACTs concern gamma-ray sources over an extremely wide interval of distances, ranging from the parsec scale for Galactic objects up to the Gigaparsec scale for the fartest detected blazar 3C279. This circumstance allows not only to infer the intrinsec properties of the sources, but also to probe the nature of photon propagation throughout cosmic distances.The latter fact is of paramount importance for very-high-energy (VHE) gamma-ray astrophysics, since the horizon of the observable Universe rapidly shrinks above 100 GeV as the energy further increases. This is due to the fact that photons from distant sources scatter off background photons permeating the Universe, thereby disappearing into electron-positron pairs [1]. It turns out that the corresponding cross section σ(γγ → e + e − ) peaks where the VHE photon energy E and the background photon energy ǫ are related by ǫ ≃ (500 GeV/E) eV. As far as observations performed by IACTs are concerned, the cosmic opacity is dominated by the interaction with ultraviolet/optical/infrared diffuse background photons 1 , usually called Extragalactic Background Light (EBL), which is produced by galaxies during the whole history of the Universe. Owing to such an absorption process, photon propagation is controlled by the optical depth τ (E, D), with D denoting the source distance. Hence, the observed photon flux Φ obs (E, D) is related to the emitted one Φ em (E) byNeglecting evolutionary effects on the EBL spectral energy distribution for simplicity, the optical depth reads τ (E, D) ≃ D/λ γ (E), where λ γ (E) is the photon mean free path for γγ → e + e − referring to the present cosmic epoch. As a consequence, Eq. (1) simplifies asThe function λ γ (E) decreases like a power law from the Hubble radius 4.3 Gpc around 100 GeV to 1 Mpc around 100 TeV [2]. Now, Eq. (2) entails that the observed flux is exponentially suppressed 1 Frequency band 1.2 · 10 3 GHz − 1.2 · 10 6 GHz, corresponding to the wavelength range 0.25 µm − 250 µm.

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Predicted High Energy Break in the Isotropic Gamma Ray Spectrum: a Test of Cosmological Origin

Cited by 135 publications

References 5 publications

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

Effects of spatial fluctuations in the extragalactic background light on hard gamma-ray spectra

A new light boson from MAGIC observations?

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