BEXCO - Room E(106/107)
[GA168] HESS discovery of very-high-energy emission from the blazar PKS0736+017: on the location of the γ-ray emitting region in FSRQ
- Matteo CERRUTI
With the installation of a new 28-m diameter imaging atmospheric Cherenkov telescope in the middle of the array, the H.E.S.S. instrument has entered since 2012 into its Phase II. The fifth large-size telescope is particularly important to lower the threshold energy of the array, and is thus an unique instrument to observe low-frequency-peaked blazars, such as flat-spectrum radio-quasars (FSRQs), which remain rare in the very-high- energy (VHE; E > 100 GeV) γ-ray domain. In this contribution, we report on the discovery with the H.E.S.S. telescopes of VHE γ-ray emission from the FSRQ PKS 0736+017 (z=0.189). H.E.S.S. observations were triggered as a target-of-opportunity in February 2015 following the detection of γ-ray flaring activity in the MeV-GeV energy-band with Fermi-LAT. Significant VHE emission is detected with H.E.S.S. only during one of the nights of the observing campaign, showing at least night- by-night variability in the VHE regime. The very detection of PKS 0736+017 as VHE emitter probes that the γ-ray emitting region has to be located downstream in the jet, beyond the broad-line-region, in order to avoid significant absorption by pair-production.