A Focusing X-Ray Timing Observatory

The next generation X-ray timing observatory will be a more powerful and versatile facility if it is based upon focusing optics rather than large area detectors. With X-ray CCDs or active pixel detectors (or possibly even microcalorimeters) in the focal plane(s) the spectral resolution will be significantly superior to the RXTE PCA making it possible to study the dynamics of the gravitationally redshifted Fe line in great detail. With orders of magnitude reduction of background the ability to study temporal variations of fainter sources in external galaxies will be much greater than with large area counters of the same collecting area. Furthermore, source confusion will not be an issue as it may be when large area detectors observe sources near the galactic center or in other galaxies. Focusing detectors do require larger open apertures than counters and their bandwidth is smaller. However, they are not necessarily heavier and in fact one candidate optic would be much lighter