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Very high energy gamma-ray emission from SHBL J001355.9-185406 detected by HESS

ATEL # 3007; W. Hofmann (MPIK) on behalf of the H.E.S.S. collaboration
on 5 Nov 2010; 14:48 UT
Password Certification: Berrie Giebels (

Subjects: AGN
Referred to by ATEL #: 3014, 3023

The AGN SHBL J001355.9-185406 (z=0.095), selected from a list of extremely high X-ray to radio flux ratio targets in the Sedentary High energy peaked BL Lac catalog (Giommi et al. 2005, A&A, 434, 385), has been detected by the High Energy Stereoscopic System (H.E.S.S.). Using published advanced analysis methods a statistical significance of more than 5 standard deviations above 300 GeV is found in 38 hours of live time taken between July 2008 and August 2010. The light curve is compatible with a constant flux at the level of ~1% of the flux of the Crab nebula. This source is not present in the first year Fermi/LAT Catalog, indicating that its flux in the Fermi/LAT range is below the 1-year sensitivity.

The source was monitored over the same period by the Automatic Telescope for Optical Monitoring (ATOM), operated by the HESS collaboration and located next to the IACT array. No significant variability down to a timescale of a few days is present, with a mean flux of R=(15.410.03)mag and B=(17.520.05)mag. Swift observations were taken in September 2010. The X-ray spectrum can be fit by a power law model with photon index of 2.030.06 using a Galactic absorption of 2.13x1020 cm-2 (Kalberla et al. 2005). The corresponding 2-10 keV flux is (6.70.4)x10-12 erg cm-2 s-1.

H.E.S.S. is an array of four imaging atmospheric Cherenkov telescopes for the detection of gamma-ray sources above 100 GeV located in the Khomas highlands in Namibia. It was constructed and is operated by researchers from Germany, France, UK, South Africa, Poland, the Czech Republic, Ireland, Australia, Austria, Sweden, Armenia, and the host country, Namibia.

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