Evidence for VHE γ-ray emission from the distant BL Lac PG 1553+113

Link:
Erscheinungsjahr:
2006
Medientyp:
Text
Schlagworte:
  • BL lacertae objects : individual : PG1553+113
  • galaxies : active
  • gamma rays : observations
Beschreibung:
  • 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 (4.8 ± 1.3stat ± 1.0syst) × 10 -12 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 Γ = 4.0 ± 0.6). Although the redshift of PG 1553+113 is unknown, there are strong indications that it is greater than z = 0.25 and possibly larger than z = 0.78. 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 z <0.74. © ESO 2006.
Lizenz:
  • info:eu-repo/semantics/openAccess
Quellsystem:
Forschungsinformationssystem der UHH
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Quelldatensatz
oai:www.edit.fis.uni-hamburg.de:publications/a58e11fd-9e94-4183-96e6-462a916708ac