Measurement of the extragalactic background light using MAGIC and Fermi-LAT gamma-ray observations of blazars up to z = 1

Abstract

We present a measurement of the extragalactic background light (EBL) based on\na joint likelihood analysis of 32 gamma-ray spectra for 12 blazars in the\nredshift range z = 0.03 to 0.944, obtained by the MAGIC telescopes and\nFermi-LAT. The EBL is the part of the diffuse extragalactic radiation spanning\nthe ultraviolet, visible and infrared bands. Major contributors to the EBL are\nthe light emitted by stars through the history of the universe, and the\nfraction of it which was absorbed by dust in galaxies and re-emitted at longer\nwavelengths. The EBL can be studied indirectly through its effect on very-high\nenergy photons that are emitted by cosmic sources and absorbed via\nphoton-photon interactions during their propagation across cosmological\ndistances. We obtain estimates of the EBL density in good agreement with\nstate-of-the-art models of the EBL production and evolution. The 1-sigma upper\nbounds, including systematic uncertainties, are between 13% and 23% above the\nnominal EBL density in the models. No anomaly in the expected transparency of\nthe universe to gamma rays is observed in any range of optical depth.We also\nperform a wavelength-resolved EBL determination, which results in a hint of an\nexcess of EBL in the 0.18 - 0.62 $\\mu$m range relative to the studied models,\nyet compatible with them within systematics.\n