High-redshift Blazars through NuSTAR Eyes

The most powerful sources among the blazar family are MeV blazars. Often detected at z > 2, they usually display high X- and gamma-ray luminosities, larger-than-average jet powers, and black hole masses ≳10<SUP>9</SUP> M <SUB>&sun;</SUB>. In the present work, we perform a multiwavelength study of three high-redshift blazars 3FGL J0325.5+2223 (z = 2.06), 3FGL J0449.0+1121 (z = 2.15), and 3FGL J0453.2-2808 (z = 2.56), analyzing quasi-simultaneous data from GROND, Swift-UVOT and XRT, Nuclear Spectroscopic Telescope Array (NuSTAR), and Fermi-LAT. Our main focus is on the hard X-ray band recently unveiled by NuSTAR (3--79 keV) where these objects show a hard spectrum that enables us to constrain the inverse Compton (IC) peak and the jet power. We found that all three targets resemble the most powerful blazars, with the synchrotron peak located in the submillimeter range and the IC peak in the MeV range, and therefore belong to the MeV blazar class. Using a simple one-zone leptonic emission model to reproduce the spectral energy distributions, we conclude that a simple combination of synchrotron and accretion disk emission reproduces the infrared--optical spectra, while the X-ray to gamma-ray part is well reproduced by the IC scattering of low-energy photons supplied by the broad-line region. The black hole masses for each of the three sources are calculated to be ≳4 10<SUP>8</SUP> M <SUB>&sun;</SUB>. The three studied sources have jet power at the level of, or beyond, the accretion luminosity.