Hard X-ray detection of the high-redshift quasar 4C 71.07

BATSE/OSSE observations of the high-redshift quasar 4C 71.07 indicate that this is the brightest and farthest active galactic nucleus so far detected above 20 keV. BATSE Earth occultation data have been used to search for emissions from 4C 71.07 from nearly 3 yr of observation. The mean source flux over the whole period in the BATSE energy range 20-100 keV is (1.32 +/- 0.11) x 10(-10) ergs cm(-2) s(-1), corresponding to a luminosity of 2 x 10(48) ergs s(-1). The BATSE light curve over the 3 yr of observations shows several flarelike events, one of which tin 1996 January) is associated with an optical flare (R = 16.1) but with a delay of 55 days. The OSSE/BATSE spectral analysis indicates that the source is characterized by a flat power spectrum (Gamma similar to 1.1-1.3) when in a low state; this spectral form is consistent within errors with the ASCA and ROSAT spectra. This means that the power law observed from 0.1 to 10 keV extends up to at least 1 MeV, but steepens soon after to meet EGRET high-energy data. BATSE data taken around the 1996 January flare suggest that the spectrum could be steeper when the source is in a bright state. The vFv representation of the source is typical of a low-frequency-peaked/gamma-ray-dominated blazar, with the synchrotron peak in the millimeter-far-infrared band and the Compton peak in the MeV band. The BATSE and OSSE spectral data seem to favor a model in which the high-energy flux is due to the sum of the synchrotron self-Compton and the external Compton contributions; this is also supported by the variability behavior of the source.