CONSTRAINING THE POPULATION OF HIGH-SPIN SUPERMASSIVE BLACK HOLES IN THE EARLY U

There are four massive quasars discovered at z>5. These sources present apuzzle; how black holes grow to 10^9 solar masses in the limited age of theuniverse. We would like to address this by estimating the population of suchobjects. The population estimation requires good constraints on their jetproperties, in particular, the Doppler factor. We propose to observe thehighredshift blazar SDSSJ013127.34032100.1 with XMM and NuSTAR for 40 ks and100 ks, respectively, in order to model the broadband SED accurately. Thebroadband Xray observation will allow us to measure the Doppler factor for thesource, constraining the higha supermassive BH population in the earlyuniverse. These measurements will be used to infer the number of similar BHs at high redshifts. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]