Ted Schultz

First results from a next-generation off-plane X-ray diffraction grating

Future NASA X-ray spectroscopy missions will require high throughput, high resolving power grating spectrometers. Off-plane reflection gratings are capable of meeting the performance requirements needed to realize the scientific goals of these missions. We have identified a novel grating fabrication method that utilizes common lithographic and microfabrication techniques to produce the high fidelity groove profile necessary to achieve this performance. Application of this process has produced an initial pre-master that exhibits a radial (variable line spacing along the groove dimension), high density (> 6000 grooves/mm), laminar profile. This pre-master has been tested for diffraction efficiency at the BESSY II synchrotron light facility and diffracts up to 55 % of incident light into usable spectral orders. Furthermore, tests of spectral resolving power show that these gratings are capable of obtaining resolving powers well above 1300 (λ/Δλ) with limitations due to the test apparatus, not the gratings. Obtaining these results has provided confidence that this fabrication process is capable of producing off-plane reflection gratings for the next generation of X-ray observatories.

The assembly, calibration, and preliminary results from the Colorado high-resolution Echelle stellar spectrograph (CHESS)

The Colorado High-resolution Echelle Stellar Spectrograph (CHESS) is a far ultraviolet (FUV) rocket-borne experiment designed to study the atomic-to-molecular transitions within translucent interstellar clouds. CHESS is an objective echelle spectrograph operating at f/12.4 and resolving power of 120,000 over a band pass of 100 – 160 nm. The echelle flight grating is the product of a research and development project with LightSmyth Inc. and was coated at Goddard Space Flight Center (GSFC) with Al+LiF. It has an empirically-determined groove density of 71.67 grooves/mm. At the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado (CU), we measured the efficiencies of the peak and adjacent dispersion orders throughout the 90 – 165 nm band pass to characterize the behavior of the grating for pre-flight calibrations and to assess the scattered-light behavior. The crossdispersing grating, developed and ruled by Horiba Jobin-Yvon, is a holographically-ruled, low line density (351 grooves/mm), powered optic with a toroidal surface curvature. The CHESS cross-disperser was also coated at GSFC; Cr+Al+LiF was deposited to enhance far-UV efficiency. Results from final efficiency and reflectivity measurements of both optics are presented. We utilize a cross-strip anode microchannel plate (MCP) detector built by Sensor Sciences to achieve high resolution (25 μm spatial resolution) and data collection rates (~ 106 photons/second) over a large format (40mm round, digitized to 8k x 8k) for the first time in an astronomical sounding rocket flight. The CHESS instrument was successfully launched from White Sands Missile Range on 24 May 2014. We present pre-flight sensitivity, effective area calculations, lab spectra and calibration results, and touch on first results and post-flight calibration plans.

Results from the Extended X-ray Off-plane Spectrometer (EXOS) Sounding Rocket Payload

We present results from the Extended X-ray Off-Plane Spectrometer (EXOS) sounding rocket payload. The payload was launched on November 13, 2009 and successfully obtained a spectrum of the Cygnus Loop Supernova Remnant. The instrument observed in the ~20 - 110 Angstrom bandpass with high resolution (~50) by utilizing an offplane reflection grating array. This payload is also the 2nd flight for a relatively new type of detector, the Gaseous Electron Multiplier (GEM) detector. We discuss the performance of these technologies in flight, as well as an overview of our plans for the next flight of this design.

Flight performance and first results from the sub-orbital local interstellar cloud experiment (SLICE)

We present the flight performance and preliminary science results from the first flight of the Sub-orbital Local Interstellar Cloud Experiment (SLICE). SLICE is a rocket-borne far-ultraviolet instrument designed to study the diffuse interstellar medium. The SLICE payload comprises a Cassegrain telescope with LiF-coated aluminum optics feeding a Rowland Circle spectrograph operating at medium resolution (R ~ 5000) over the 102 – 107 nm bandpass. We present a novel method for cleaning LiF-overcoated Al optics and the instrumental wavelength calibration, while the details of the instrument design and assembly are presented in a companion proceeding (Kane et al. 2013). We focus primarily on first results from the spring 2013 launch of SLICE in this work. SLICE was launched aboard a Terrier-Black Brant IX sounding rocket from White Sands Missile Range to observe four hot stars sampling different interstellar sightlines. The instrument acquired approximately 240 seconds of on-target time for the science spectra. We observe atomic and molecular transitions (HI, OI, CII, OVI, H2) tracing a range of temperatures, ionization states, and molecular fractions in diffuse interstellar clouds. Initial spectral synthesis results and future plans are discussed.

The opto-mechanical design of the sub-orbital local interstellar cloud experiment (SLICE)

We present the fabrication and testing of the Sub-orbital Local Interstellar Cloud Experiment (SLICE), a rocket-borne payload for ultraviolet astrophysics in the 1020 to 1070 Å bandpass. The SLICE optical system is composed of an ultraviolet-optimized telescope feeding a Rowland Circle spectrograph. The telescope is an 8-inch Classical Cassegrain operating at F/7, with Al optics overcoated with LiF for enhanced far-ultraviolet reflectivity. The holographically-ruled grating focuses light at an open-faced microchannel plate detector employing an opaque RbBr photocathode. In this proceeding, we describe the design trades and calibration issues confronted during the build-up of this payload. We place particular emphasis on the technical details of the design, modifications, construction, and alignment procedures for SLICE in order to provide a roadmap for the optimization of future ruggedized experiments for ultraviolet imaging and spectroscopy.

Pushing the boundaries of X-ray grating spectroscopy in a suborbital rocket

The Off-Plane Grating Rocket Experiment (OGRE) will greatly advance the current capabilities of soft X-ray grating spectroscopy and provide an important technological bridge towards future X-ray observatories. The OGRE sounding rocket will fly an innovative X-ray spectrograph operating at resolving powers of R ~ 2000 and effective areas < 100 cm2 in the 0.2–1.5 keV bandpass. This represents a factor of two improvement in spectral resolution over currently operating instruments. OGRE will observe the astrophysical X-ray calibration source Capella, which has a linedominated spectrum and will showcase the full capabilities of the OGRE spectrograph. We outline the mission design for OGRE and provide detailed overviews of relevant technologies to be integrated into the payload, including slumped glass mirrors, blazed reflection gratings customized for the off-plane mount, and electron-multiplying CCDs (EMCCDs). The OGRE mission will bring these components to a high technology readiness level, paving the way for the use of such a spectrograph on future X-ray observatories or Explorer-class missions.

An introduction to the water recovery x-ray rocket

The Water Recovery X-ray Rocket (WRXR) is a sounding rocket payload that will launch from the Kwajalein Atoll in April 2018 and seeks to be the first astrophysics sounding rocket payload to be water recovered by NASA. WRXRs primary instrument is a grating spectrometer that consists of a mechanical collimator, X-ray reflection gratings, grazing-incidence mirrors, and a hybrid CMOS detector. The instrument will obtain a spectrum of the diffuse soft X-ray emission from the northern part of the Vela supernova remnant and is optimized for 3rd and 4th order OVII emission. Utilizing a field of view of 3.25° × 3.25° and resolving power of λ/δλ ≈40-50 in the lines of interest, the WRXR spectrometer aims to achieve the most highly-resolved spectrum of Velas diffuse soft X-ray emission. This paper presents introductions to the payload and the science target.

The CODEX sounding rocket payload

We present the CODEX sounding rocket payload, a soft x-ray (0.1-1.0 keV) spectrometer designed to observe diffuse high-surface brightness astronomical sources. The payload is composed of two modules, each with a 3.25° x 3.25° field of view defined by a stack of wire grids that block light not coming to a 3.0 m focus and admit only nearly-collimated light onto an array of 67 diffraction gratings in an off-plane mount. After a 2.0 m throw, the spectrum is detected by offset large-format gaseous electron multiplier (GEM) detectors. CODEX will target the Vela supernova remnant later this year to measure the temperature and abundances and to determine the contributions of various soft x-ray emission mechanisms to the remnants energy budget; resulting spectra will have resolution (E/▵E) ranging from 50 to 100 across the band. CODEX is the third-generation of similar payloads from the University of Colorado, with an increased bandpass, higher throughput, and a more robust mechanical structure than its predecessors.

The EXOS sounding rocket payload

We present an overview of the Extended X-ray Off-Plane Spectrometer (EXOS) Sounding Rocket Payload based at the University of Colorado, Boulder. The program includes a total of four launches over the next four years on various x-ray sources. The payload utilizes off-plane reflection gratings and Gaseous Electron Multiplier (GEM) detectors in order to achieve both high throughput and resolution (R~100).

Development of the x-ray camera for the OGRE sub-orbital rocket

Current theories regarding the matter composition of the universe suggest that half of the expected baryonic matter is missing. One region this could be residing in is intergalactic filaments which absorb strongly in the X-ray regime. Present space based technology is limited when it comes to imaging at these wavelengths and so new techniques are required. The Off-Plane Grating Rocket Experiment (OGRE) aims to produce the highest resolution spectrum of the binary star system Capella, a well-known X-ray source, in the soft X-ray range (0.2keV to 2keV). This will be achieved using a specialised payload combining three low technology readiness level components placed on-board a sub-orbital rocket. These three components consist of an array of large format off-plane X-ray diffraction gratings, a Wolter Type 1 mirror made using single crystal silicon, and the use of EM-CCDs to capture soft X-rays. Each of these components have been previously reviewed with OGRE being the first project to utilise them in a space observation mission. This paper focuses on the EM-CCDs (CCD207-40 by e2v) that will be used and their optimisation with a camera purposely designed for OGRE. Electron Multiplying gain curves were produced for the back-illuminated devices at -80C. Further tests which will need to be carried out are discussed and the impact of the OGRE mission on future projects mentioned.