2006/11/27 by D. Mazin, F. Göebel, F. Goebel · 1 citation
Physics and Astronomy · #Absorption (acoustics) #Astrophysics #Astrophysics and Cosmic Phenomena #Blazar #Dark Matter and Cosmic Phenomena #Extragalactic background light #Galaxy #Gamma ray #Limit (mathematics) #Lyman limit #MAGIC (telescope) #Optics #Photon #Physics #Quasar #Radio Astronomy Observations and Technology #Redshift #astro-ph
paper · pdf · doi:10.1086/511751
published as Astrophys.J.655:L13-L16,2007 · revised version submitted to ApJ
arxiv created 2006/11/27 · openalex publication_date 2007/01/10 · arxiv updated 2009/12/01 · openalex created_date 2019/06/27 · openalex updated_date 2026/08/05
PG 1553+113 is a known BL Lac object, newly detected in the GeV-TeV energy range by H.E.S.S. and MAGIC. The redshift of this source is unknown and a lower limit of z > 0.09 was recently estimated. The very high energy (VHE) spectrum of PG 1553+113 is attenuated due to the absorption by the low-energy photon field of the extragalactic background light (EBL). Here we correct the combined H.E.S.S. and MAGIC spectrum of PG 1553+113 for this absorption assuming a minimum density of the evolving EBL. We use an argument that the intrinsic photon index cannot be harder than Γ = 1.5 and derive an upper limit on the redshift of z < 0.69. Moreover, we find that a redshift above z = 0.42 implies a possible break of the intrinsic spectrum at ~200 GeV. Assuming that such a break is absent, we derive a much stronger upper limit of z < 0.42. Alternatively, this break might be attributed to an additional emission component in the jet of PG 1553+113. This would be the first evidence for a second component detected in the VHE spectrum of a blazar.