Probing the extragalactic mid-infrared background with HAWC

Abstract

The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the EBL density directly is challenging, especially in the near- to far-infrared waveband, mainly due to the zodiacal light foreground. Instead, gamma-ray astronomy offers the possibility to indirectly set limits on the EBL by studying the effects of gamma-ray absorption in the very high energy (VHE:$>$100 GeV) spectra of distant blazars. The High Altitude Water Cherenkov gamma ray observatory (HAWC) is one of the few instruments sensitive to gamma rays with energies above 10 TeV. This offers the opportunity to probe the EBL in the near/mid IR region: $\lambda$ = 1 $\mu$m - 100 $\mu$m. In this study, we fit physically motivated emission models to Fermi Large Area Telescope (LAT) GeV data to extrapolate the intrinsic TeV spectra of blazars. We then simulate a large number of absorbed spectra for different randomly generated EBL model shapes and calculate Bayesian credible bands in the EBL intensity space by comparing and testing the agreement between the absorbed spectra and HAWC extragalactic observations of two blazars. The resulting bands are in agreement with current EBL lower and upper limits, showing a downward trend towards higher wavelength values $\lambda >10\mu$m also observed in previous measurements.

Submitted to ApJ

References in corpus (6)

• New constraints on the Mid-IR EBL from the HESS discovery of VHE gamma rays from 1ES 0229+200
• New limits on the density of the extragalactic background light in the optical to the far-infrared from the spectra of all known TeV blazars
• Measurement of the EBL spectral energy distribution using the VHE gamma-ray spectra of H.E.S.S. blazars
• Measurement of the extragalactic background light spectral energy distribution with VERITAS
• Systematic Physical Characterization of the Gamma-Ray Spectra of 2FHL Blazars
• Testing one-zone synchrotron-self-Compton models with spectral energy distributions of Mrk 421