Blazars radiate from radio through gamma-ray frequencies and thereby make ideal targets for
multifrequency studies. Such studies allow the properties of the emitting jet to be constrained.
3C 279 is among the most notable blazars and therefore subject to extensive multifrequency
campaigns. We report the results of a campaign ranging from near-IR to gamma-ray energies
that targeted an outburst of 3C 279 in 2015 June. The campaign pivots around the detection
in only 50 ks by INTEGRAL, whose IBIS/ISGRI data pin down the high-energy component
of the spectral energy distribution (SED) between Swift-XRT data and Fermi-LAT data. The
overall SED from near-IR to gamma rays can be well represented by either a leptonic or a lepto-
hadronic radiation transfer model. Even though the data are equally well represented by the two
models, their inferred parameters challenge the physical conditions in the jet. In fact, the leptonic
model requires parameters with a magnetic field far below equipartition with the relativistic
particle energy density. In contrast, equipartition may be achieved with the lepto-hadronic model,
although this implies an extreme total jet power close to the Eddington luminosity.