Calibration and Performance of the REgolith X-Ray Imaging Spectrometer (REXIS) Aboard NASA's OSIRIS-REx Mission to Bennu

• Main Authors: Hong, Jaesub, Binzel, Richard P, Allen, Branden, Guevel, David, Grindlay, Jonathan, Hoak, Daniel, Masterson, Rebecca, Chodas, Mark, Lambert, Madeline, Thayer, Carolyn, Bokhour, Ed, Biswas, Pronoy, Mendenhall, Jeffrey A, Ryu, Kevin, Kelly, James, Warner, Keith, Lim, Lucy F, Bartels, Arlin, Lauretta, Dante S, Boynton, William V, Enos, Heather L, Harshman, Karl, Balram-Knutson, Sara S, Polit, Anjani T, McCoy, Timothy J, Clark, Benton C
• Format: Journal Article
• Language: English
• Published: 14-10-2021
• Subjects: Physics - Earth and Planetary Astrophysics; Physics - Instrumentation and Methods for Astrophysics
• DOI: 10.48550/arxiv.2110.07690

The REgolith X-ray Imaging Spectrometer (REXIS) instrument on board NASA's
OSIRIS-REx mission to the asteroid Bennu is a Class-D student collaboration
experiment designed to detect fluoresced X-rays from the asteroid's surface to
measure elemental abundances. In July and November 2019 REXIS collected ~615
hours of integrated exposure time of Bennu's sun-illuminated surface from
terminator orbits. As reported in Hoak et al. (2021), the REXIS data do not
contain a clear signal of X-ray fluorescence from the asteroid, in part due to
the low incident solar X-ray flux during periods of observation. To support the
evaluation of the upper limits on the detectable X-ray signal that may provide
insights for the properties of Bennu's regolith, we present an overview of the
REXIS instrument, its operation, and details of its in-flight calibration on
astrophysical X-ray sources. This calibration includes the serendipitous
detection of the transient X-ray binary MAXI J0637-430 during Bennu
observations, demonstrating the operational success of REXIS at the asteroid.
We convey some lessons learned for future X-ray spectroscopy imaging
investigations of asteroid surfaces.