A METHOD FOR SETTING UPPER LIMITS TO THE EXTRAGALACTIC BACKGROUND LIGHT WITH FERMI-LAT AND TeV OBSERVATIONS OF BLAZARS

Journal Article · Sat May 01 04:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/714/1/L157· OSTI ID:21448938

Georganopoulos, Markos ^[1]; Finke, Justin D ^[2]; Reyes, Luis C ^[3]

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1. Department of Physics, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 (United States)
2. U.S. Naval Research Laboratory, Code 7653, 4555 Overlook Ave SW, Washington, DC 20375-5352 (United States)
3. Kavli Institute for Cosmological Physics (KIPC) at the University of Chicago, Chicago, IL 60637 (United States)

We propose a method for setting upper limits to the extragalactic background light (EBL). Our method uses simultaneous Fermi-LAT and ground-based TeV observations of blazars and is based on the assumption that the intrinsic spectral energy distribution (SED) of TeV blazars lies below the extrapolation of the Fermi-LAT SED from GeV to TeV energies. By extrapolating the Fermi-LAT spectrum, which for TeV blazars is practically unattenuated by photon-photon pair production with EBL photons, a firm upper limit on the intrinsic SED at TeV energies is provided. The ratio of the extrapolated spectrum to the observed TeV spectrum provides upper limits to the optical depth for the propagation of the TeV photons due to pair production on the EBL, which in turn sets firm upper limits to EBL models. We demonstrate our method using simultaneous observations from Fermi-LAT and ground-based TeV telescopes of the blazars PKS 2155-304 and 1ES 1218+304, and show that high EBL density models are disfavored. We also discuss how our method can be optimized and how Fermi and X-ray monitoring observations of TeV blazars can guide future TeV campaigns, leading to potentially much stronger constraints on EBL models.

• OSTI ID: 21448938
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 714; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BASIC INTERACTIONS
BOSONS
COSMIC RADIO SOURCES
ELECTROMAGNETIC INTERACTIONS
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY RANGE
ENERGY SPECTRA
GALAXIES
GAMMA RADIATION
INTERACTIONS
IONIZING RADIATIONS
MASSLESS PARTICLES
PAIR PRODUCTION
PARTICLE INTERACTIONS
PARTICLE PRODUCTION
PHOTON-PHOTON INTERACTIONS
PHOTONS
QUASARS
RADIATIONS
SPECTRA
TELESCOPES
TEV RANGE