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The Unprecedented VHE Gamma-ray Outburst of PKS 1510-089 in May 2016

PKS 1510-089 (z=0.361), one of only a handful of flat spectrum radio quasars (FSRQ) detected in the very high energy (VHE, E > 100 GeV) gamma-rays, is known for its flux variability and complex multiwavelength behaviour. VHE observations by H.E.S.S. and MAGIC in May 2016 detected an unprecedented flare, both in intensity and in the shortness of its variability timescale. The flare lasted less than 48 hours, during which time the flux reached about 80 per cent of the Crab Nebula flux above 200 GeV. In addition, the intranight variability of this source was detected for the first time. Simultaneous observations in high energy (HE, E > 100 MeV) gamma-rays performed with Fermi-LAT and optical R-band performed with ATOM show behaviour not consistent with simple simultaneous brightening in all bands. While a significant hardening of the spectrum is visible in HE, the flux increased only moderately. A simultaneous rise in daily-averaged optical flux was seen in the R-band. However, the intranight flux evolution shows two prominent peaks, while only one is visible in the VHE range. These intriguing features of the flare will be presented in detail. We will also discuss possible explanations for the observed emission.

Blazars, Relativistic jets, VHE gamma-rays, PKS1510-089

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