  The radio-loud quasar SDSS J114657.79+403708.6 at a redshift z=5.0 is one of
the most distant radio-loud objects. The IR-optical luminosity and spectrum
suggest that its black hole has a very large mass: M=(5+-1)x 1e9 Msun. The
radio-loudness (ratio of the radio to optical flux) of the source is large
(around 100), suggesting that the source is viewed at small angles from the jet
axis, and could be a blazar. The X-ray observations fully confirm this
hypothesis, due to the high level and hardness of the flux. This makes SDSS
J114657.79+403708.6 the third most distant blazar known, after Q0906+693
(z=5.47) and B2 1023+25 (z=5.3). Among those, SDSS J114657.79+403708.6 has the
largest black hole mass, setting interesting constraints on the mass function
of heavy (larger than one billion solar masses) black holes at high redshifts.
