A GeV-TeV Measurement of the Extragalactic Background Light

The extragalactic background light (EBL) can be probed via the absorption imprint it leaves in the spectra of gamma- ray sources (gamma gamma -> e(-)e(+)). We recently developed a dedicated technique to reconstruct the EBL, and its evolution with redshift, from gamma-ray optical depth data using a large sample of blazars detected by the Fermi Large Area Telescope. Here, we extend this data set to the TeV regime using ground-based Cherenkov observations of 38 blazars and report the first homogeneous measurement of the EBL spectral intensity covering the ultraviolet to infrared wavelengths (similar to 0.1-100 mu m). A minimal EBL throughout the wavelength range with respect to integrated galaxy light is found, allowing little additional unresolved emission from faint or truly diffuse populations setting an upper limit of less than or similar to 4. nW m(-2) sr(-1) at 1.4 mu m. In particular, the cosmic optical background at z = 0 is found to be 27.8(-2.0)(+2.1) nW m(-2) sr(-1). This work lays the foundation for accurate gamma-ray measurements of the EBL across its whole spectral range using a combination of GeV and TeV data.