Observations of the soft X-ray background with the XQC microcalorimeter sounding rocket

Abstract On March 28, 1999 the X-ray Quantum Calorimeter (XQC) sounding rocket instrument completed its third flight to observe the soft X-ray background in the 0.02–1.0 keV energy band. The detector system is a 36-pixel ion implanted microcalorimeter array with 0.5×2.0 mm HgTe absorbers that is operated at 60 mK with a single-stage adiabatic demagnetization refrigerator. The detector array, mounting system, thin film filters and dewar infrastructure have all undergone substantial improvements since the last flight. The result is a scientifically successful observation of the diffuse soft X-ray background that reveals several emission lines from highly ionized elements in the interstellar medium. Preliminary results show strong emission from both O VII and O VIII. In this paper, we discuss problems and their solutions for this mature Low-Temperature Detector (LTD) instrument and recent astrophysical results.