TeV Detection of the Extreme HSP Blazar RBS 1366 by VERITAS

Extreme high-synchrotron-peak blazars (EHSPs) are postulated as the most efficient and extreme particle accelerators in the universe but remain enigmatic as a possible new class of TeV gamma-ray blazars. Blazars are active galactic nuclei (AGNs) with jets of relativistic particles that generate non-thermal emission pointed along the line-of-sight. Their spectral energy distribution (SED) are characterized by synchrotron and inverse-Compton peaks, indicating acceleration of leptonic and possibly hadronic particle populations in the jet. EHSPs are characterized by a peak synchrotron frequency > 10¹⁷ Hz with their Compton peak expected to fall in the TeV range. Indeed, the handful of EHSPs detected by Imaging Air Cherenkov Telescopes (IACTs) have presented challenges where some may be a high-frequency extension of the blazar sequence while others peaking around 10 TeV may represent a different class of TeV emitters. Detections of the high-energy and very-high-energy (HE; E > 100 MeV, VHE; E > 100 GeV) components of the Compton peak will play an important role in constraining the acceleration model derived from the SED. We present the discovery of TeV emission from RBS 1366, a candidate EHSP, by the VERITAS observatory. Using HE and VHE data from the Fermi-LAT and VERITAS observatories, respectively, we characterize the detection by providing an SED and model fit in the context of other EHSP candidates. Our work confirms the status of RBS 1366 as an EHBL.