PKS 1510-089 ( z=0.361 ) is one of only a handful of flat spectrum radio quasars that have been detected at very high energy ( VHE , E > 100 GeV ) gamma rays .
It is a very active source across the entire electromagnetic spectrum .
VHE observations in May 2016 with H.E.S.S .
and MAGIC revealed an exceptionally strong flare , which lasted for less than two nights , and exhibited a peak flux of about 0.8 times the flux of the Crab Nebula above 200 GeV .
The flare provides the first evidence of intranight variability at VHE in this source .
While optical observations with ATOM reveal a counterpart at optical frequencies , Fermi -LAT observations reveal only low flux variability at high energy ( HE , E > 100 MeV ) gamma rays .
Interestingly , the HE spectral index significantly hardens during the peak of the VHE flare , indicating a strong shift of the peak frequency of the high energy component .
Given the expected strong absorption due to the broad-line region , the VHE emission region can not be located deep within that region .