Paul B. Reid

Toward Active X-ray Telescopes II

In the half century since the initial discovery of an astronomical (non-solar) x-ray source, the observation time required to achieve a given sensitivity has decreased by eight orders of magnitude. Largely responsible for this dramatic progress has been the refinement of the (grazing-incidence) focusing x-ray telescope, culminating with the exquisite subarcsecond imaging performance of the Chandra X-ray Observatory. The future of x-ray astronomy relies upon the development of x-ray telescopes with larger aperture areas (< 1 m2) and comparable or finer angular resolution (< 1″). Combined with the special requirements of grazing-incidence optics, the mass and envelope constraints of space-borne telescopes render such advances technologically challenging—requiring precision fabrication, alignment, and assembly of large areas (< 200 m2) of lightweight (≈ 1 kg m-2 areal density) mirrors. Achieving precise and stable alignment and figure control may entail active (in-space adjustable) x-ray optics. This paper discusses relevant programmatic and technological issues and summarizes current progress toward active x-ray telescopes.

Thermal forming of glass substrates for adjustable optics (Conference Presentation)

The proposed Lynx telescope is an X-ray observatory with Chandra-like angular resolution and about 30 times larger effective area. The technology under development at SAO is based on the deposition of piezoelectric material on the back of glass substrates, used to correct longer wavelength figure errors. This requires a large number (about 8000) of figured segments with sufficient quality to be in the range of correctibility of the actuators. Thermal forming of thin glass offers a convenient approach, being based on intrinsically smooth surfaces (which doesn’t require polishing or machining), available in large quantity and at a low cost from flat display industry. Being a replica technique, this approach is particularly convenient both for development and for the realization of modular/segmented telescopes. In this paper we review the current status and the most recent advances in the thermal forming activities at SAO, and the perspectives for the employment of these substrates for the adjustable X-Ray optics.

Arcus: the x-ray grating spectrometer explorer (Conference Presentation)

Arcus, a Medium Explorer (MIDEX) mission, was selected by NASA for a Phase A study in August 2017. The observatory provides high-resolution soft X-ray spectroscopy in the 12-50 A bandpass with unprecedented sensitivity: effective areas of >350 cm^2 and spectral resolution >2500 at the energies of O VII and O VIII for z=0-0.3. The Arcus key science goals are (1) to measure the effects of structure formation imprinted upon the hot baryons that are predicted to lie in extended halos around galaxies, groups, and clusters, (2) to trace the propagation of outflowing mass, energy, and momentum from the vicinity of the black hole to extragalactic scales as a measure of their feedback and (3) to explore how stars, circumstellar disks and exoplanet atmospheres form and evolve. Arcus relies upon the same 12m focal length grazing-incidence silicon pore X-ray optics (SPO) that ESA has developed for the Athena mission; the focal length is achieved on orbit via an extendable optical bench. The focused X-rays from these optics are diffracted by high-efficiency Critical-Angle Transmission (CAT) gratings, and the results are imaged with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest. Arcus will be launched into an ~ 7 day 4:1 lunar resonance orbit, resulting in high observing efficiency, low particle background and a favorable thermal environment. Mission operations are straightforward, as most observations will be long (~100 ksec), uninterrupted, and pre-planned. The baseline science mission will be completed in <2 years, although the margin on all consumables allows for 5+ years of operation.

Progress in development of adjustable optics for x-ray astronomy

Adjustable X-ray optics is the technology under study by SAO and PSU for the realization of the proposed X-ray telescope Lynx. The technology is based on thin films of lead-zirconate-titanate (PZT) deposited on the back of thermally formed thin substrates, and represents a potential solution to the challenging trade-off between high-surface quality and low mass, that limits the performance of current generation of X-ray telescopes. The technology enables the correction of mirror fabrication figure, mounting induced distortions, and on-orbit correction for variations in the mirror thermal environment. We describe the current state of development, presenting updated test data, anticipation of performances and expectations.