We report the first detection of very-high-energy \gamma -ray emission above 100 GeV ( VHE ) gamma-ray emission above 140 GeV from PKS 1424+240 , a BL Lac object with an unknown redshift .
The photon spectrum above 140 GeV measured by VERITAS is well described by a power law with a photon index of 3.8 \pm 0.5 _ { \mathrm { stat } } \pm 0.3 _ { \mathrm { syst } } and a flux normalization at 200 GeV of ( 5.1 \pm 0.9 _ { \mathrm { stat } } \pm 0.5 _ { \mathrm { syst } } ) \times 10 ^ { -11 } TeV ^ { -1 } cm ^ { -2 } s ^ { -1 } , where \mathrm { stat } and \mathrm { syst } denote the statistical and systematical uncertainty , respectively .
The VHE flux is steady over the observation period between MJD 54881 and 55003 ( 2009 February 19 to June 21 ) .
Flux variability is also not observed in contemporaneous high energy observations with the Fermi Large Area Telescope ( LAT ) .
Contemporaneous X-ray and optical data were also obtained from the Swift XRT and MDM observatory , respectively .
The broadband spectral energy distribution ( SED ) is well described by a one-zone synchrotron self-Compton ( SSC ) model favoring a redshift of less than 0.1 .
Using the photon index measured with Fermi in combination with recent extragalactic background light ( EBL ) absorption models it can be concluded from the VERITAS data that the redshift of PKS 1424+240 is less than 0.66 .