Intermediate Mass Black Holes
There is a class of luminous, variable, point-like X-ray sources found in many nearby galaxies that may have inferred isotropic luminosities hundreds of times larger than the expected maximum luminosity of a stellar mass black hole. This has led to speculation that some of these ultra-luminous X-ray sources (ULX) may form a new class of black holes with masses in the range from about 100-2000 solar masses, so called intermediate-mass black holes (IMBH). Currently there are 20-30 of these sources known which can be resolved from nearby emission with a 15 arcsec angular resolution.
Constellation-X will spectroscopically conÞrm the presence of cool accretion disks in IMBH candidates. Currently there are ~6 ULX sources with significant detections of a soft thermal spectral component consistent with an accretion disk with an average inner edge temperature of ~0.15 keV (Miller, Fabian and Miller 2004). Perhaps more importantly, Constellation-X will detect relativistic iron K-shell emission lines if they are present. Detection of these lines would conÞrm the disk origin of the soft X-ray emission, and would strongly rule out beaming arguments for the high inferred luminosities. If Constellation-X conÞrms the existence of IMBHs, then X-ray probes of General Relativity will be possible across an enormous range of black hole masses.
X-ray timing measurements can identify the characteristic timescales on which the objects are variable. By comparing studies of supermassive black holes with those of stellar mass black holes in our Galaxy, it has been shown that the characteristic variability times scale with black hole mass.
