Very high energy gamma-ray emission detected from PKS 1440-389 with H.E.S.S.

The BL Lac object PKS 1440-389, located at a tentative redshift of z=0.065 (6dF Galaxy Survey, Jones, D.H. et al. MNRAS 355, 747-763, 2004), has been reported as a hard (G=1.75+/-0.05), bright, and steady extragalactic source at GeV energies in the Fermi-LAT catalogue (2FGL J1443.9-3908, P.L. Nolan et al., 2012, ApJS, 199, 31). The extrapolation of the Fermi-LAT spectrum to very high energies (VHE; E> 100 GeV), together with its brightness in the radio and X-ray bands, makes this BL Lac object a good candidate for VHE emission. PKS 1440-389 was observed with H.E.S.S. for ~6h in the past two months, resulting in a signal exceeding 5 standard deviation above an energy threshold of ~200 GeV in the preliminary onsite analysis. The preliminary flux is estimated to be ~3% of the flux of the Crab Nebula above 200 GeV. No significant variability has been detected in the H.E.S.S. data. In the optical, the source has been observed with the ATOM telescope (M. Hauser et al. AN, 325, 659, 2004) resulting in mean fluxes of 15.33+/-0.06 mag and 15.23+/-0.06 mag in B and R band, respectively. H.E.S.S. will continue observing the source for the coming weeks (current observation window: until April 30; next observation window: May 11-28) and observations at other wavelengths are encouraged. H.E.S.S. is an array of four imaging atmospheric Cherenkov telescopes for the detection of VHE gamma-ray sources located in the Khomas highlands in Namibia. It was constructed and is operated by researchers from Armenia, Australia, Austria, the Czech Republic, France, Germany, Ireland, Poland, South Africa, Sweden, UK, and the host country, Namibia