Browsing by Author "Zhang, William W."
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Item AXIS Advanced X-ray Imaging Satellite(2019-03-11) Mushotzky, Richard F.; Aird, James; Barger, Amy J.; Cappelluti, Nico; Chartas, George; Corrales, Lia; Eufrasio, Rafael; Fabian, Andrew C.; Falcone, Abraham D.; Gallo, Elena; Gilli, Roberto; Grant, Catherine E.; Hardcastle, Martin; Hodges-Kluck, Edmund; Kara, Erin; Koss, Michael; Li, Hui; Lisse, Carey M.; Loewenstein, Michael; Markevitch, Maxim; Meyer, Eileen T.; Miller, Eric D.; Mulchaey, John; Petre, Robert; Ptak, Andrew J.; Reynolds, Christopher S.; Russell, Helen R.; Safi-Harb, Samar; Smith, Randall K.; Snios, Bradford; Tombesi, Francesco; Valencic, Lynne; Walker, Stephen A.; Williams, Brian J.; Winter, Lisa M.; Yamaguchi, Hiroya; Zhang, William W.Much of the baryonic matter in the Universe, including the most active and luminous sources, are best studied in the X-ray band. Key advances in X-ray optics and detectors have paved the way for the Advanced X-ray Imaging Satellite (AXIS), a Probe-class mission that is a major improvement over Chandra, which has generated a steady stream of important discoveries for the past 2 decades. AXIS can be launched in the late 2020s and will transform our understanding in several major areas of astrophysics, including the growth and fueling of supermassive black holes, galaxy formation and evolution, the microphysics of cosmic plasmas, the time-variable universe, and a wide variety of cutting-edge studies. Relative to Chandra, the AXIS PSF is nearly twice as sharp on-axis; its field of view for subarcsecond imaging 70 times larger by area; its effective area at 1 keV is 10 times larger. The low-Earth orbit ensures a low and stable detector background, resulting in 50 times greater sensitivity than Chandra for extended sources. AXIS has a rapid repointing response with operations similar to Swift, but is 100 times more sensitive for time-domain science. These capabilities open up a vast discovery space and complement the next generation of astronomical observatories. A high-spectral-resolution mission (Athena) operating at the same time as a high-angular-resolution mission (AXIS) greatly increases the range of scientific discovery. AXIS will use lightweight X-ray optics made of thin single-crystal silicon mirrors developed at NASA Goddard. The detector array builds on a long legacy of X-ray CCD and provides improved photon localization, much faster readout time, and broader energy band. The estimated mission costs are consistent with the $1B Probe mission cost guideline.Item CONFIRMATION OF A HIGH MAGNETIC FIELD IN GRO J1008−57(IOP Publishing, 2014-08-21) Bellm, Eric C.; Fürst, Felix; Pottschmidt, Katja; Tomsick, John A.; Boggs, Steven E.; Chakrabarty, Deepto; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Stern, Daniel; Walton, Dominic J.; Wilms, Jörn; Zhang, William W.GRO J1008−57 is a high-mass X-ray binary for which several claims of a cyclotron resonance scattering feature near 80 keV have been reported. We use NuSTAR, Suzaku, and Swift data from its giant outburst of 2012 November to confirm the existence of the 80 keV feature and perform the most sensitive search to date for cyclotron scattering features at lower energies. We find evidence for a 78⁺³₋₂ keV line in the NuSTAR and Suzaku data at >4σ significance, confirming the detection using Suzaku alone by Yamamoto et al. A search of both the phase-averaged and phase-resolved data rules out a fundamental at lower energies with optical depth larger than 5% of the 78 keV line. These results indicate that GRO J1008−57 has a magnetic field of 6.7 × 10¹²(1 + z) G, the highest among known accreting pulsars.Item Looking at A 0535+26 at low luminosities with NuSTAR(EDP Sciences, 2017-12-12) Ballhausen, Ralf; Pottschmidt, Katja; Fürst, Felix; Wilms, Jörn; Tomsick, John A.; Schwarm, Fritz-Walter; Stern, Daniel; Kretschmar, Peter; Caballero, Isabel; Harrison, Fiona A.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Zhang, William W.We report on two NuSTAR observations of the high-mass X-ray binary A 0535+26 taken toward the end of its normal 2015 outburst at very low 3–50 keV luminosities of ~1.4 × 1036 erg s⁻¹ and ~5 × 10³⁵ erg s⁻¹, which are complemented by nine Swift observations. The data clearly confirm indications seen in earlier data that the source’s spectral shape softens as it becomes fainter. The smooth exponential rollover at high energies seen in the first observation evolves to a much more abrupt steepening of the spectrum at 20–30 keV. The continuum evolution can be nicely described with emission from a magnetized accretion column, modeled using the compmag model modified by an additional Gaussian emission component for the fainter observation. Between the two observations, the optical depth changes from 0.75 ± 0.04 to 0.56⁺⁰.⁰¹₋₀.₀₄, the electron temperature remains constant, and there is an indication that the column decreases in radius. Since the energy-resolved pulse profiles remain virtually unchanged in shape between the two observations, the emission properties of the accretion column reflect the same accretion regime. This conclusion is also confirmed by our result that the energy of the cyclotron resonant scattering feature (CRSF) at ~45 keV is independent of the luminosity, implying that the magnetic field in the region in which the observed radiation is produced is the same in both observations. Finally, we also constrain the evolution of the continuum parameters with the rotational phase of the neutron star. The width of the CRSF could only be constrained for the brighter observation. Based on Monte Carlo simulations of CRSF formation in single accretion columns, its pulse phase dependence supports a simplified fan beam emission pattern. The evolution of the CRSF width is very similar to that of the CRSF depth, which is, however, in disagreement with expectations.Item Mass manufacturing of high resolution and lightweight monocrystalline silicon X-ray mirror modules(SPIE, 2019-09-09) Biskach, Michael P.; Allgood, Kim D.; Chan, Kai-Wing; Hlinka, Michal; Kearney, John D.; Numata, Ai; Mazzarella, James R.; Riveros, Raul E.; Saha, Timo T.; Solly, Peter M.; Zhang, William W.Astronomical observations of distant and faint X-ray sources will expand our understanding of the evolving universe. These challenging science goals require X-ray optical elements that are manufactured, measured, coated, aligned, assembled, and tested at scale. The Next Generation X-ray Optics (NGXO) group at NASA Goddard Space Flight Center is developing solutions to the challenges faced in planning, constructing, and integrating X-ray optics for future telescopes such as the Lynx Large Mission concept for the Astro2020 Decadal Survey on Astronomy and Astrophysics, Probe Mission concepts AXIS, TAP, and HEX-P, the Explorer Mission concepts STAR-X and FORCE and the sub-orbital mission OGRE. The lightweight mirror segments, efficiently manufactured from blocks of commercially available monocrystalline silicon, are coated, aligned, and fixed in modular form. This paper discusses our first attempt to encapsulate our technology experience and knowledge into a model to meet the challenge of engineering and production of the many modules required for a spaceflight mission. Through parallel lines of fabrication, assembly, and testing, as well as the use of existing high throughput industrial technologies, ∼104 coated X-ray mirror segments can be integrated into ∼103 modules adhering to a set budget and schedule that survive environmental testing and approach the diffraction limit.Item Next generation x-ray optics for astronomy: high resolution, lightweight, and low cost(SPIE, 2019-09-09) Zhang, William W.; Allgood, Kim D.; Biskach, Michael P.; Chan, Kai-Wing; Hlinka, Michal; Kearney, John; Mazzarella, James; McClelland, Ryan S.; Numata, Ai; Riveros, Dr. Raul E.; Saha, Dr. Timo T.; Solly, Peter M.The capability of an X-ray telescope depends on the quality of its mirror, which can be characterized by four quantities: point-spread-function, photon-collecting area, field of view, and energy bandwidth. In this paper, we report on our effort of developing an X-ray mirror technology that advances all of those four quantities for future X-ray astronomical missions. In addition, we have adopted a modular approach, capable of making mirror assemblies for missions of all sizes, from large missions like Lynx, to medium-sized Probes like AXIS, TAP, and HEX-P, to Explorers like STAR-X and FORCE, and to small sub-orbital missions like OGRE. This approach takes into account that all X-ray telescopes must be space-borne and therefore require their mirror assemblies be lightweight. It is designed to make use of modern mass production techniques and commercial off-the-shelf equipment and materials to maximize production throughput and thereby to minimize implementation schedule and costs.Item NuSTAR AND SWIFT OBSERVATIONS OF THE BLACK HOLE CANDIDATE XTE J1908+094 DURING ITS 2013 OUTBURST(IOP Publishing, 2015-09-18) Tao, Lian; Tomsick, John A.; Walton, Dominic J.; Fürst, Felix; Kennea, Jamie; Miller, Jon M.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Gandhi, Poshak; Grefenstette, Brian W.; Hailey, Charles J.; Harrison, Fiona A.; Krimm, Hans A.; Pottschmidt, Katja; Stern, Daniel; Tendulkar, Shriharsh P.; Zhang, William W.The black hole (BH) candidate XTE J1908+094 went into outburst for the first time since 2003 in 2013 October. We report on an observation with the Nuclear Spectroscopic Telescope Array (NuSTAR) and monitoring observations with Swift during the outburst. NuSTAR caught the source in the soft state: the spectra show a broad relativistic iron line, and the light curves reveal a ∼40 ks flare, with the count rate peaking about 40% above the non-flare level and with significant spectral variation. A model combining a multi-temperature thermal component, a power law, and a reflection component with an iron line provides a good description of the NuSTAR spectrum. Although relativistic broadening of the iron line is observed, it is not possible to constrain the BH spin with these data. The variability of the power-law component, which can also be modeled as a Comptonization component, is responsible for the flux and spectral change during the flare, suggesting that changes in the corona (or possibly continued jet activity) are the likely cause of the flare.Item Recent advances in the alignment of silicon mirrors for high-resolution x-ray optics(SPIE, 2019-09-09) Chan, Kai-Wing; Mazzarella, James R.; Saha, Timo T; Zhang, William W.; Biskach, Michael P.; Numata, Ai; Riveros, Dr. Raul E.; McClelland, Ryan S.; Solly, Peter M.Recent advances in the fabrication of segmented silicon mirrors make it possible to build large-area, lightweight, high-resolution x-ray telescopes with arc-second angular resolution. To build such a telescope, we fabricate accurate silicon mirrors and develop alignment and bonding techniques to precisely align and integrate these silicon mirror segments into modular units. In this way, the processes of mirror fabrication, mirror alignment and bonding, and subsequent integration into units of successive larger scale are completely independent, and their technologies can be developed independently. In this paper, we present recent improvement in the precision of optical alignment and mirror bonding. We discuss the measurement of the mirror’s focusing in a parallel optical beam and address the practical challenges in bonding these mirrors into modules as an intermediate step to build up a full-scale telescope for space missions.