0420024

We propose to observe with INTEGRAL PKS 0537-286 the most distant gamma-loud QSO. PKS 0537-286 is the best candidate for the broad band spectroscopy capabilities of INTEGRAL. Detected in the optical radio soft X-ray and at GeV energies PKS 0537-286 was recently (yet unpublished) revealed by Swift-BAT as a constant hard X-ray source (15-150 keV). PKS 0537-286 is a flat spectrum radio quasar (FSRQ) and a member of the MeV blazar class blazars whose spectral energy distribution (SED) peaks at MeV energies. Among all the blazars the high-z FSRQs are the best target to settle the open question about the emission processes. In fact for such objects the high energy emission peaks at the overlap of the X- and gamm-ray energy band which is covered by INTEGRAL. It is at the overlap of these two energy bands that the contribution of external radiation fields to the synchrotron genereted photons can be assessed and emission processes distinguished. With its very hard photon index (~1.1) this object is the perfect target for the broad band capabilities of INTEGRAL. In 1 Ms of observation the combined JEM-X and ISGRI spectrum would extend from 3 to 300 keV achieving in both instrument a >15 sigma level detection. This would be the most sensitive measurement of the hard X-ray/soft gamma-ray spectrumof a FSRQ and would adequately sample the inverse Compton (IC) component in a way to detect the spectral curvature and allow a precise meausurement of the IC peak.The INTEGRAL observation will be coordinated with AGILE (>100 MeV) and with Swift-XRT ( < 3keV ) contemporary observations. [truncated! Please see actual data for full text]