Optimizations of Pt/SiC and W/Si multilayers for the Nuclear Spectroscopic Telescope Array

Abstract

The Nuclear Spectroscopic Telescope Array, NuSTAR, is a NASA funded Small Explorer Mission, SMEX, scheduled for launch in mid 2011. The spacecraft will fly two co-aligned conical approximation Woltcr-I optics with a focal length of 10 meters. The mirrors will be deposited with Pt/SiC and W lSi multilayers to provide a broad band reflectivity from 6 keY up to 78.1 keY. To optimize the mirror coating we use a Figure of Merit procedure developed for gazing incidence optics, which averages the effective area over the energy range, and combines an energy weighting function with an angular weighting function to control the shape of the desired effective area.The NuSTAR multilayers are depth graded with a power-law, d i = al(b + i)C, and we optimize over the total number of bi-layers, N, c, and the maximum bi-layer thickness, d max . The reslllt is a 10 mirror group design optimized for a flat even energy response both on and off-axis.

THE LACK OF DIFFUSE, NON-THERMAL HARD X-RAY EMISSION IN THE COMA CLUSTER: THESWIFTBURST ALERT TELESCOPE'S EYE VIEW

“…Ultimately, a true detection of IC emission from Coma will have to wait for upcoming missions with focusing hard Xray telescopes, namely NuSTAR 8 and Astro-H. 9 For NuSTAR to achieve a sensitivity comparable to our upper limits, a single pointed observation of at least 100 ks will be required (Madsen et al 2009). However, the much finer spatial resolution will remove the uncertainty associated with bright background active galactic nuclei (AGNs) and allow multiple spatially resolved joint fits.…”

NuSTAR observatory science operations: on-orbit acclimation

“…The X-ray optics and detector benches are separated by a stiff mast that includes a mechanism with the capability of making small adjustments to optimize the location of the optical axis on the focal plane detectors (see Fig.1). The X-ray optics bench consists of two Wolter-I conical approximation 3 mirror modules, each with 133 shells coated with multiple layers of W/Si and Pt/C, limiting the highest efficient reflectivity to the Pt 78.4 keV K-edge 4,5,6 . The focal plane bench is mounted on the spacecraft bus and consists of two independent solid state photon counting detector modules (FPMA & B), each with a 2x2 array of CdZnTe (CZT) crystal detectors, surrounded by CsI anti-coincidence shielding.…”

Observational artifacts of Nuclear Spectroscopic Telescope Array: ghost rays and stray light

“…A multilayer is a stack of two alternating material pairs, called a bilayer, and, in the case of NuSTAR, the bilayer thicknesses are graded with thicker layers at the top for low-energy reflection and thinner layers at the bottom for the high-energy reflection. 8,9 The angle of the innermost shell with respect to the optical axis (OA) is α primary;shell¼1 ¼ 1.342 mrad (4.6′) and α p;133 ¼ 4.715 mrad (26.3′) for the outermost shell. The angle of the secondary mirror is related to the primary by α s ¼ 3α p .…”

“…The mean effective area between 3 and 5 keV [black curve in Fig. 12(b)] is obtained from the raytrace using the mean SiO 2 reflectivities between 3 and 5 keV for the first reflection and the NuSTAR multilayer recipes 9 for the second reflection. We did not include the optics thermal cover and detector window Be absorption, and the area has been scaled to the photons falling on the detector area only.…”