The Solid Redshift Lower Limit of the Most Distant TeV-Emitting Blazar PKS 1424+240

We present the newly determined redshift lower limit of the very-high-energy (VHE; E>100 GeV) detected blazar PKS 1424+240. No VHE-detected blazar has shown solid spectroscopic evidence of being more distant. This redshift limit is firmly placed through the detection of Lyman forest features in new far-ultraviolet spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph. The blazar is sufficiently distant so that past VHE observations sample historically large opacity values, extending beyond 4 if assuming low levels of extragalactic background light (EBL) and beyond 5 for high levels of EBL. We show the unexpected spectral shape of the absorption-corrected Compton peak, using the contemporaneous VERITAS and Fermi Large Area Telescope observations during the time of VHE emission discovery.