Enabling decadal science with a combined, parallelized approach to microcalorimeter calibration in the soft x-ray waveband

The Line Emission Mapper (LEM), an x-ray astrophysics probe concept, will use an array of x-ray microcalorimeters to map emission lines from 0.1–2 keV with 1–2 eV FWHM energy resolution over a wide field of view (30 arcmin x 30 arcmin). The science that can be obtained with LEM is broad, but the main goal is to provide a comprehensive look at the physics of galaxy formation, including the stellar and black hole feedback and flows of baryonic matter into and out of galaxies. This mission science goal and much of LEM’s observatory science require the spectrometer meet a calibration accuracy of ~0.5 eV across the science waveband for the energy gain scale–the mapping of measured detector signal to incident photon energy. Achieving this accuracy requires careful calibration and characterization on the ground. Traditionally, x-ray microcalorimeter gain calibration has used fluorescent sources where a commercial x-ray tube induces fluorescence line emission off of solid targets. These relatively inexpensive and compact x-ray sources provide sufficiently high flux to enable measurements within affordable time frames. However, these characteristic fluorescent lines suffer from complicated line profiles with shapes that are difficult or impossible to calculate theoretically to high accuracy. Instrument teams use empirical models of the natural line shapes to characterize the detectors, but for many of the key energy bands these line shapes and centroids have uncertainties that are too large to accurately constrain the detector resolution and gain scale. This problem is worse for lower-Z targets that provide emission lines below 1.5 keV, a key energy range for LEM, because the satellite lines are larger, closer to the main peaks, and vary based on target chemical composition and details of the incident x-ray spectrum. In contrast, the energies and line shapes of K-shell transitions from highly charged ions, e.g., in He- and H-like ions, are generally known to very high accuracy, and are routinely produced using Electron Beam Ion Traps (EBITs). For this reason, EBITs have been included in calibration plans for XRISM’s Resolve and Athena’s X-ray Integral Field Unit. However, owing to an EBIT’s much larger form factor and lower line flux compared to the compact fluorescence sources, measurements using an EBIT pose challenges to ground calibration campaigns and can strain mission development schedules. Here, we propose to develop a new approach to x-ray calorimeter gain calibration leveraging key attributes of both methods. The goal is to simplify the calibration programs for future missions and reduce their cost. We will show that we can calibrate transfer standards with sufficient precision to satisfy the energy scale calibration requirements. In the end, this will mean LEM can develop calibrated fluorescence sources for ground calibration campaigns, and will only need EBITs to calibrate the fluorescence targets (in parallel with other development activities), omitting lengthy EBIT measurements during the flight-instrument ground calibration campaigns, which require high staffing levels and are often on the project’s critical path. The proposed work will use the EBIT facility at Lawrence Livermore National Laboratory, home to state-of-the-art x-ray microcalorimeters and a suite of high-resolution dispersive spectrometers. We will pair a fluorescence source with an EBIT, placing them in front of the same spectrometers, thus calibrating the fluorescence lines against the well known He-like and H-like lines and providing high accuracy empirical reference models. The work will verify this new approach to enable straightforward LEM instrument calibration with minimal loss of accuracy. We will choose line complexes most suitable for LEM, but the work can be used for any future or existing mission. The new models will also be useful for on-board calibration sources and detector development.

The Astrophysics Research and Analysis program (APRA) supports suborbital and suborbital-class investigations, development of detectors and supporting technology, laboratory astrophysics, and limited ground-based observing. Basic research proposals in these areas are solicited for investigations that are relevant to NASA's programs in astronomy and astrophysics, including the entire range of photons, gravitational waves, and particle astrophysics. The emphasis of this solicitation is on technologies and investigations that advance NASA astrophysics missions and goals.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.