GRAZING-INCIDENCE FE-LINE TELESCOPES USING W B4C MULTILAYERS/

The loss of throughput observed at higher energies for traditional gra zing-incidence x-ray telescopes coated with high-Z elements can be par tly countered by employing multilayers on the outermost reflectors. Us ing 8-keV reflectivity data from a periodic W/B4C multilayer, the expe cted performance of intermediate-sized telescopes of (1) the nested Ki rkpatrick-Baez geometry and (2) the conical approximation to a nested Wolter-I geometry is computed. Depending on the multilayer design, the throughput was increased by a factor of 3 to 5 in a 1.5-keV-wide band , or by 30% to 100% in a 3-keV-wide band. This gain is obtained at the expense of a 20% to 30% loss of throughput over the 2-to 4-keV band. These designs lend themselves well to astrophysics missions, such as s pectroscopy of the H- and He-like iron emission lines (6.4 to 7.1 keV) . The technology for multilayer coating, mounting, and configuring of the flat reflectors required by the Kirkpatrick-Baez telescope exists, so that an Fe-line multilayer telescope could be built today.