The optical variability of the magic blazar PKS 1222+216
KS 1222+216 (redshift z=0.432) is a FSRQ that in the gamma energy range, has shown a particularly active behaviour with flares also in the Very High Energy domain (e.g. E > 100 GeV). MAGIC detect a flare in June 2010, in cincidence with a huge GeV emission recorded by AGILE and Fermi. PKS 1222+216 is thus the third FSRQ, after 3C279 (z=0.536) and PKS 1510-089 (z=0.36), observed at such high energy. We investigate the optical spectral properties of this blazar during a period of more than 3 years. While the continuum is highly variable the broad line emission is practically constant. This supports a scenario in which the broad line region is not affected by jet continuum variations. We thus infer the thermal component of the continuum from the line luminosity and we show that it is comparable with the continuum level observed during the phases of minimum optical activity. We can thus estimate, also in the case of an extremly variable object, the mass of the black hole through the virial method from the FWHM of MgII, HBeta, and HAlpha broad lines and from the thermal continuum luminosity. This yields a black hole mass value of ~6x10E8 solar masses.
About the talk
Università dell'Insubria & INFN Milano Bicocca; Italy