089043

While future soft X-ray (0.5--2 keV) surveys are being designed to discover high-redshift (z and amp amp amp gt 9) heavy-seed mass black holes (hsBHs) with M BH virgul 10^5 M SUN a rest-frame hard X-ray spectral model is crucial to understand how many hsBHs can be detected. Motivated by this we propose a simultaneous 70-ksec NuSTAR and 20-ksec XMM-Newton observation to a local AGN in POX 52 with M BH virgul 3x10^5 M SUN and L 2-10 virgul 10^42 erg s^-1 resembling the future targets. While there are two expected X-ray models: (1) a power-law with low-energy cutoff like ultra-luminous X-ray sources and (2) one with high-energy cutoff and reflected emission like Seyfert galaxies the superior sensitivity of NuSTAR above 10 keV will distinguish them and provide a reliable hard X-ray spectral template. [truncated! Please see actual data for full text]