The Challenges of Developing a New Approach to High-Resolution X-Ray Spectroscopy

Just about 40 years ago, a group of X-ray astrophysicists at the Goddard Space Flight Center sought a way to improve the energy resolution of non-dispersive X-ray spectrometers for the AXAF observatory (now Chandra). What emerged was something entirely different – the thermal detection of individual X-rays and measuring their energies with extreme precision. This came about through the confluence of IR and X-ray laboratories and a rapid proof-of concept demonstration program leading to a successful proposal to implement an instrument on an early version of AXAF.

Over the subsequent decades, the technology was developed and refined, and eventually incorporated into space-flight instruments. The X-ray calorimeter was used starting in the 1990’s to measure the spectrum of the diffuse X-ray background on the XQC suborbital payload, has been used for many laboratory plasma measurements relevant to X-ray astronomy, and was finally deployed in 2016 to measure the X-ray spectrum of the Perseus cluster of galaxies on the Astro-H (Hitomi) observatory. What was found was surprising and beautifully illustrated the power of imaging spectroscopy with X-ray calorimeters.

In this talk, we tell the story of this transformational technology, discuss some of the optimization phase space for different applications, and describe upcoming instruments and possible new instruments that use X-ray calorimeters for high-efficiency, high-resolution spectroscopy.