NuSTAR, Swift, and GROND observations of the flaring MeV blazar: PMN
  J0641$-$0320
  MeV blazars are a sub--population of the blazar family, exhibiting
larger--than--average jet powers, accretion luminosities and black hole masses.
Because of their extremely hard X--ray continua, these objects are best studied
in the X-ray domain. Here, we report on the discovery by the $Fermi$ Large Area
Telescope and subsequent follow-up observations with $NuSTAR$, $Swift$ and
GROND of a new member of the MeV blazar family: PMN J0641$-$0320. Our optical
spectroscopy provides confirmation that this is a flat--spectrum radio quasar
located at a redshift of $z=1.196$. Its very hard $NuSTAR$ spectrum (power--law
photon index of $\sim$1 up to $\sim$80 keV) indicates that the emission is
produced via inverse Compton scattering off photons coming from outside the
jet.The overall spectral energy distribution of PMN J0641$-$0320 is typical of
powerful blazars and by reproducing it with a simple one-zone leptonic emission
model we find the emission region to be located either inside the broad line
region or within the dusty torus.
