H.E.S.S. and MAGIC observations of a sudden cessation of a very-high-energy <i>γ</i>-ray flare in PKS 1510−089 in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510−089 is known for its complex multiwavelength behaviour and it one of only a few FSRQs detected in very-high-energy (VHE, E &gt; 100 GeV) γ rays. VHE -ray observations with H.E.S.S. MAGIC late May early June 2016 resulted the detection an unprecedented flare, which revealed, first time, intranight variability this source. While common timescale 1.5 h has been found, there significant deviation near end ∼20 min marking cessation event. peak flux nearly two orders magnitude above low-level emission. For curvature was 1510–089, can be fully explained by absorption on part extragalactic background light. Optical R -band ATOM revealed counterpart even though detailed evolution differs from light curve. Interestingly, steep decrease observed at same time as flare. In high-energy (HE, MeV) band, moderate increase Fermi -LAT, while HE significantly hardens up to photon index 1.6. A search broad-line region (BLR) features indicates that emission located outside BLR. Radio very-long-baseline interferometry reveal fast-moving knot interacting standing jet feature around As ∼50 pc black hole, flare may have distance hole. If indeed true correlation, rays must produced far down jet, where turbulent plasma crosses shock.