Challenging the one zone SSC model in VHE gamma ray emitting BL lacs The interesting case of PKS 1424+240

The BL Lac object PKS 1424+240 with uncertain redshift has been investigated by the MAGIC imaging atmospheric Cherenkov telescopes at very high energies (VHE; E> 100 GeV) since 2006. The source was observed in various emission states and the integral flux above 150 GeV shows hints of variability. We present a detailed analysis of the multi-frequency emission, from radio to VHE gamma rays. We show that a simple one-zone synchrotron self Compton (SSC) model is inadequate to account for the observed spectral behavior. In particular, the synchrotron peak is much broader than the high-energy peak and the separation between the two peaks is large, which requires high Doppler factor for modeling. We investigate the correlation between lightcurves in several wavebands and propose a two-zone SSC model to fit the experimental data where part of the observed emission is due to a parsec scale jet and the remaining part to a more compact region close to the central engine.