scholarly journals GAMMA-RAYS FROM BLAZARS AND THE EXTRAGALACTIC BACKGROUND LIGHT

2013 ◽  
Vol 22 (13) ◽  
pp. 1330025 ◽  
Author(s):  
LUIGI COSTAMANTE
Keyword(s):  
Gamma Rays ◽  
Far Infrared ◽  
High Energy ◽  
Extragalactic Background Light ◽  
Background Light ◽  
Theoretical Progress ◽  
Very High Energy ◽  
Very High

Recent observations of blazars at high energy (0.1–100 GeV) and very high energy (> 0.1 TeV) have provided important constraints on the intensity and spectrum of the diffuse extragalactic background light (EBL), shedding light on its main origin. Several issues remain open, however, in particular in the mid- and far-infrared bands and in the blazar emission at multi-TeV energies. This review summarizes the observational and theoretical progress in the study of the EBL with gamma-rays and the most promising future improvements, which are mainly expected from spectra in the multi-TeV range.

scholarly journals VERY HIGH ENERGY GAMMA RAYS FROM e± PAIR HALOS

2009 ◽  
Vol 18 (06) ◽  
pp. 911-927 ◽  
Author(s):  
A. EUNGWANICHAYAPANT ◽  
F. AHARONIAN
Keyword(s):  
Energy Spectrum ◽  
Gamma Rays ◽  
High Energy ◽  
Angular Distributions ◽  
Extragalactic Background Light ◽  
Electron Positron ◽  
Very High Energy ◽  
Energy Gamma ◽  
Electron Positron Pair ◽  
Very High

In this paper we study the formation of giant electron–positron pair halos around the powerful high energy extragalactic sources. We investigate the dependence of radiation of pair halos, in particular the spectral and angular distributions on the energy spectrum of the primary gamma rays, the redshift of the source, and the flux of the extragalactic background light.

scholarly journals Effect of axion-like particles on the spectrum of the extragalactic gamma-ray background

2021 ◽  
Vol 2021 (11) ◽  
pp. 030
Author(s):  
Yun-Feng Liang ◽  
Xing-Fu Zhang ◽  
Ji-Gui Cheng ◽  
Hou-Dun Zeng ◽  
Yi-Zhong Fan ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Small Region ◽  
High Energy ◽  
Extragalactic Background Light ◽  
Background Light ◽  
Very High Energy ◽  
The Universe ◽  
Very High

Abstract Axion-like particles (ALPs) provide a feasible explanation for the observed lower TeV opacity of the Universe. If the anomaly TeV transparency is caused by ALPs, then the fluxes of distant extragalactic sources will be enhanced at photon energies beyond TeV, resulting in an enhancement of the observed extragalactic gamma-ray background (EGB) spectrum. In this work, we have investigated the ALP modulation on the EGB spectrum at TeV energies. Our results show that in the most optimistic case, the existence of ALPs can cause the EGB spectrum to greatly deviate from the prediction of a pure extragalactic-background-light (EBL) absorption scenario. The deviation occurs at approximately ≳1 TeV, and the current EGB measurements by Fermi-LAT cannot identify such an effect. We also find that most of the sensitive ALP parameters have been ruled out by existing constraints, leaving only a small region of unrestricted parameters that can be probed using the EGB effect investigated in this work. Observations from forthcoming very-high-energy instruments like LHAASO and CTA may be beneficial for the study of this effect.

THE EXTRAGALACTIC BACKGROUND LIGHT: LOWER VERSUS UPPER LIMITS

2009 ◽  
Vol 18 (10) ◽  
pp. 1633-1637 ◽  
Author(s):  
MARTIN RAUE
Keyword(s):  
High Energy ◽  
Energy Spectra ◽  
Extragalactic Background Light ◽  
Background Light ◽  
Upper Limits ◽  
Very High Energy ◽  
Γ Rays ◽  
Deep Source ◽  
Lower Limits ◽  
Very High

The discovery of distant sources of very high energy (VHE) γ-rays with hard energy spectra enabled to derive strong upper limits on the density of the extragalactic background light (EBL). These limits are close to the lower limits derived from deep source counts. A recent re-dertemination of the EBL contribution from resolved sources at 3.6 μm finds a higher EBL density, which is claimed to be in conflict with the assumptions utilized to derive the EBL upper limits from VHE spectra. Here, it is shown that is possible to recover the canonical Γ ~ 1.5 intrinsic spectra for such a higher EBL density.

scholarly journals Very high-energy constraints on the infrared extragalactic background light

2019 ◽  
Vol 629 ◽  
pp. A2 ◽  
Author(s):  
A. Franceschini ◽  
L. Foffano ◽  
E. Prandini ◽  
F. Tavecchio
Keyword(s):  
Dust Emission ◽  
High Energy ◽  
Interplanetary Dust ◽  
Extragalactic Background Light ◽  
Background Light ◽  
Very High Energy ◽  
Infrared Wavelengths ◽  
Favorable Conditions ◽  
High Energy Emission ◽  
Very High

Context. Measurements of the extragalactic background light (EBL) are a fundamental source of information on the collective emission of cosmic sources. Aims. At infrared wavelengths, however, these measurements are precluded by the overwhelming dominance from interplanetary dust emission and the Galactic infrared foreground. Only at λ >  300 μm, where the foregrounds are minimal, has the infrared EBL (IR EBL) been inferred from analysis of the COBE maps. The present paper aims to assess the possibility of evaluating the IR EBL from a few micrometers up to the peak of the emission at > 100 μm using an indirect method that avoids the foreground problem. Methods. To this purpose we exploit the effect of pair-production from gamma-gamma interaction by considering the highest-energy photons emitted by extragalactic sources and their interaction with the IR EBL photons. We simulate observations of a variety of low-redshift emitters with the forthcoming Imaging Atmospheric Cherenkov Telescope (IACT) arrays (CTA in particular) and water Cherenkov observatories (LHAASO, HAWC, SWGO) to assess their suitability to constrain the EBL at such long wavelengths. Results. We find that even under the most extremely favorable conditions of huge emission flares, extremely high-energy emitting blazars are not very useful for our purpose because they are much too distant (> 100 Mpc the nearest ones, MKN 501 and MKN 421). Observations of more local AGNs displaying very high-energy emission, like low-redshift radio galaxies (M 87, IC 310, Centaurus A), are better suited and will potentially allow us to constrain the EBL up to λ ≃ 100 μm.

Deflectometric measurement of large mirrors

2014 ◽  
Vol 3 (3) ◽  
Author(s):  
Evelyn Olesch ◽  
Gerd Häusler ◽  
André Wörnlein ◽  
Friedrich Stinzing ◽  
Christopher van Eldik
Keyword(s):  
Gamma Rays ◽  
High Energy ◽  
Spherical Mirror ◽  
Large Space ◽  
Telescope Array ◽  
Spread Function ◽  
Very High Energy ◽  
Energy Gamma ◽  
Concentric Geometry ◽  
Very High

AbstractWe discuss the inspection of large-sized, spherical mirror tiles by ‘Phase Measuring Deflectometry’ (PMD). About 10 000 of such mirror tiles, each satisfying strict requirements regarding the spatial extent of the point-spread-function (PSF), are planned to be installed on the Cherenkov Telescope Array (CTA), a future ground-based instrument to observe the sky in very high energy gamma-rays. Owing to their large radii of curvature of up to 60 m, a direct PSF measurement of these mirrors with concentric geometry requires large space. We present a PMD sensor with a footprint of only 5×2×1.2 m

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