The TeV blazar measurement of the extragalactic background light

Abstract

Gamma-rays propagating through space are likely to be extinguished via electronpositron pair production off of the ambient extragalactic background light (EBL). The spectrum of the EBL is produced by starlight (and starlight reprocessed by dust) from all galaxies throughout the history of the Universe. The attenuation of 40 -400 GeV gamma-rays has been observed by Fermi and used to measure the EBL spectrum over energies 1 eV -10 eV out to redshift z ∼ 1. Measurements of several TeV blazers are consistent with attenuation, attributed to the EBL at redshift z ∼ 0.1. Here we simultaneously analyze a set of TeV blazers at z ∼ 0.1 to measure the optical depth for 100 GeV -10 TeV gamma-rays, which interact with EBL of energies 0.05 eV -5 eV. Using a suite of models for the EBL, we show that the optical depth indicated by TeV blazar attenuation is in good agreement with the optical depths measured by Fermi at lower gamma-ray energies and higher redshifts.

Probing the scale of ALP interactions with Fermi blazars

“…1 in [36] and Fig. 2 in [2]) and assign the errors in that fit to potential new physics in order to illustrate the possible constraints achievable. Here we will assume the theoretical EBL model given by [34] to be correct, and allow the error in the best-fit τ to be due to ALP physics.…”

“…We know that gamma-rays coming from distant blazars interact with the EBL, creating electron-positron pairs, and attenuating the energy spectrum [2,36]. This attenuation corresponds to an optical depth τ = τ (E, z) such that F obs = F s e −τ , where F s is the energy spectrum at the source.…”

“…In practice, neither the EBL nor the source spectra are known to a high enough level of accuracy to meaningfully constrain new physics. 2 Never-theless, we can pick a well-fit EBL model using all existing data (see figure 1 in [36] and figure 2 in [2]) and assign the errors in that fit to potential new physics in order to illustrate the possible constraints achievable. Here we will assume the theoretical EBL model given by [34] to be correct, and allow the error in the best-fit τ to be due to ALP physics.…”

“…As a test case, we consider a group of gamma-ray sources at approximately the same distance, using the high redhift (z ∼ 1) portion of the F ermi blazar catalogue [1] as an example. In addition, we discuss a similar set of TeV blazars clustered at z ∼ 0.1 (see references in [2]) . We expect blazars at the same distance to have their spectra be attenuated in a similar way by the EBL (for a recent review see [3]).…”

ESTIMATION OF THE EXTRAGALACTIC BACKGROUND LIGHT USING TeV OBSERVATIONS OF BL Lac OBJECTS

“…WhileMankuzhiyil et al (2010) used this to show the inconsistency among various EBL models interpreted theoretically,Singh et al (2014) showed a systematic deviation of the optical depths towards high energy; between the estimated and the ones predicted by various EBL models Domínguez et al (2013). used the estimated optical depths to determine the cosmic gamma ray horizon Reesman & Walker (2013). considered the EBL models byFranceschini et al (2008);Gilmore et al (2009);Domínguez et al (2011) to estimate the optical depth for the VHE sources at z ∼ 0.1.…”