Astronomy and Astrophysics · 2006 · 78 citations · 19 references
Natural SciencesAstronomyPhysicsAstrophysicsGamma-ray AstronomyObservational AstronomyContinuum EmissionExtragalactic Gamma-ray AstronomyGamma-ray SourcesGamma-ray TelescopesHigh-energy Astrophysical SourcesSpace-based Gamma-ray ObservatoriesExtragalactic Diffuse Gamma-ray BackgroundGamma-ray VariabilityHigh-energy Gamma-ray AstronomyImaging Atmospheric Cherenkov TelescopesLive Time MeasurementPhoton EmissionSpace-based Gamma-ray Telescopes
The high-frequency peaked BL Lac PG 1553+113 was observed in 2005 with the HESS stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. Using the HESS standard analysis, an excess was measured at the 4.0σ level in these observations (7.6 hours live time). Three alternative, lower-threshold analyses yield >5σ excesses. The observed integral flux above 200 GeV is cm-2 s-1, and shows no evidence for variability. The measured energy spectrum is characterized by a very soft power law (photon index of ). Although the redshift of PG 1553+113 is unknown, there are strong indications that it is greater than and possibly larger than . The observed spectrum is interpreted in the context of VHE γ-ray absorption by the Extragalactic Background Light, and is used to place an upper limit on the redshift of .
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Analysis methods for results in gamma-ray astronomy
T.-P. Li, Y.-Q. Ma · The Astrophysical Journal · 1983 · 1.3K citations