The Nuclear Spectroscopic Telescope Array (NuSTAR)

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small  Explorer mission that will carry the first focusing hard X-ray (6 - 80 keV) telescope to orbit. NuSTAR will offer a factor 50 - 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute field of view. In this talk, I will provide an overview of NuSTAR and its science goals. I will focus particularly on advances that can be made in understanding the nature of Ultraluminous X-ray sources (ULXs) by NuSTAR in partnership with XMM-Newton and Chandra. The bright X-ray emission from ULXs greatly exceeds the Eddington luminosity for a spherically accreting stellar-mass compact object, and understanding why this is so is one of the biggest mysteries in high energy astrophysics. Broadband X-ray spectroscopy from 1 - 60 keV holds a key for constraining the accretion physics in ULXs, and addressing the possibility that they harbor intermediate mass black holes.