Mon. Not. R. Astron. Soc., 446, 2267-2273 (2015/January-3)
A correlation between hard gamma-ray sources and cosmic voids along the line of sight.
FURNISS A., SUTTER P.M., PRIMACK J.R. and DOMINGUEZ A.
Abstract (from CDS):
We estimate the galaxy density along lines of sight to hard extragalactic gamma-ray sources by correlating source positions on the sky with a void catalogue based on the Sloan Digital Sky Survey (SDSS). Extragalactic gamma-ray sources that are detected at very high energy (VHE; E > 100 GeV) or have been highlighted as VHE-emitting candidates in the Fermi Large Area Telescope hard source catalogue (together referred to as `VHE-like' sources) are distributed along underdense lines of sight at the 2.4σ level. There is also a less suggestive correlation for the Fermi hard source population (1.7σ). A correlation between 10 and 500 GeV flux and underdense fraction along the line of sight for VHE-like and Fermi hard sources is found at 2.4σ and 2.6σ, calculated from the Pearson correlation coefficients of r = 0.57 and 0.47, respectively. The preference for underdense sight lines is not displayed by gamma-ray emitting galaxies within the second Fermi catalogue, containing sources detected above 100 MeV, or the SDSS Data Release 7 quasar catalogue. We investigate whether this marginal correlation might be a result of lower extragalactic background light (EBL) photon density within the underdense regions and find that, even in the most extreme case of a entirely underdense sight line, the EBL photon density is only 2 percent less than the nominal EBL density. Translating this into gamma-ray attenuation along the line of sight for a highly attenuated source with opacity τ(E, z) ∼ 5, we estimate that the attenuation of gamma-rays decreases no more than 10 percent. This decrease, although non-negligible, is unable to account for the apparent hard source correlation with underdense lines of sight.
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2014)
BL Lacertae objects: general - cosmology: miscellaneous - gamma-rays: galaxies
In Table 2, 1ES 0806+534 is a misprint for 1ES 0806+524.
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