NuSTAR - The First Focusing High Energy X-ray Mission in Orbit

The Nuclear Spectroscopic Telescope Array (NuSTAR), launched on
2012 June 13, is the first mission to carry focusing high-energy X-ray
telescopes in orbit. NuSTAR operates in the energy band from 3 to 79 keV,
extending the sensitivity of focusing far beyond the ~10 keV high-energy
cutoff achieved by all previous X-ray satellites. NuSTAR consists of two
co-aligned X-ray optics coated with Pt/C and W/Si multi-layers with focal
length of 10 meter to efficiently focus X-rays up to 79 keV. The focal plane
of each optic contains four, 2 mm thick, CdZnTe (Cadmium-Zinc-Telluride) pixel
detectors arranged in 2 x 2 array, each with an active collecting area of
2 cm x 2 cm. Each detector is divided into 32 x 32 pixels with pitch of
605 micron, that gets readout using custom-made low-noise ASICs. These
detectors have gone through a rigorous calibration campaign to determine the
energy and spatial response to incident X-rays. The inherently low background
associated with focusing the X-ray light enables NuSTAR to probe the hard X-ray
sky with a more than 100-fold improvement in sensitivity compared to previous
missions operating at similar energy band. The CdZnTe detectors on-board NuSTAR
have demonstrated the power of large band gap semi-conductors coupled with an
ASIC for astrophysical applications. During this talk I will discuss the
instrumental aspects of NuSTAR, particularly the characterization and calibration
of CdZnTe pixel detectors for the two focal plane modules of NuSTAR and describe
our on-going efforts to improve detectors for potential use with future
missions. I will also talk about post-launch activities of NuSTAR including in-orbit
calibration and quality check for the data.