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At least 55 records · Page 3

Expected level of self-Compton scattering in radio loud quasars

Radio-loud quasars usually contain parsec-scale nonthermal jets. The most compact emission region ('the core'), and perhaps some of the moving 'knots', are expected to be efficient producers of inverse Compton scattered X-rays and gamma-rays since many of the synchrotron photons will upscatter before escaping. Through multifrequency flux density observations and Very Long Baseline Interferometry (VLBI) measurements of angular sizes, one can predict the flux density of this self-Compton high-energy emission. It is not always the case that the brightest synchrotron sources are also the brightest X-ray and gamma-ray sources. Perhaps a better predictor of high-energy brightness is the ratio of hard X-ray to high-frequency radio emission. Using the synchrotron self-Compton relations, we predict the gamma-ray fluxes of several sources we expect to be detected by the Energetic Gamma Ray Experiment Telescope (EGRET). More accurate predictions will be made when we complete a program of contemporaneous radio-submillimeter and X-ray observations during the course of the EGRET all-sky survey.

Bloom, Steven D.↗

Advanced optical instruments technology

The science objectives for proposed NASA missions for the next decades push the state of the art in sensitivity and spatial resolution over a wide range of wavelengths, including the x-ray to the submillimeter. While some of the proposed missions are larger and more sensitive versions of familiar concepts, such as the next generation space telescope, others use concepts, common on the Earth, but new to space, such as optical interferometry, in order to provide spatial resolutions impossible with other concepts. However, despite their architecture, the performance of all of the proposed missions depends critically on the back-end instruments that process the collected energy to produce scientifically interesting outputs. The Advanced Optical Instruments Technology panel was chartered with defining technology development plans that would best improve optical instrument performance for future astrophysics missions. At this workshop the optical instrument was defined as the set of optical components that reimage the light from the telescope onto the detectors to provide information about the spatial, spectral, and polarization properties of the light. This definition was used to distinguish the optical instrument technology issues from those associated with the telescope, which were covered by a separate panel. The panel identified several areas for optical component technology development: diffraction gratings; tunable filters; interferometric beam combiners; optical materials; and fiber optics. The panel also determined that stray light suppression instruments, such as coronagraphs and nulling interferometers, were in need of general development to support future astrophysics needs.

Shao, Mike↗

3C 279 Multiwavelength Monitoring: The Ground-Based Campaign - 2

The optically violently variable quasar 3C 279 was monitored simultaneously from radio to gamma-ray frequencies in 1992 December - 1993 January. We report a detailed study of the ground-based results from radio to optical wavelengths. These data show that 3C 279 has a typical blazar spectrum, slightly rising at radio frequency and then progressively steeper above a first turnover frequency between 37 and 90 GHz. In the millimeter wavelength region, a simple power law is not an adequate description of the spectrum. We suggest that the millimeter "shoulder" corresponds to an additional emission component, self-absorbed between 150 and 375 GHz, possibly associated with the detachment of a new Very Long Base Interferometry (VLBI) knot and with the start of radio flare. A flux increase of 20% over 20 days was observed at 37 and 90 GHz, while contemporaneously the R-band flux doubled in about two weeks. The lack of strong variability in contemporaneous X-ray light curves (possible X-ray variations are less than 30%) implies no direct (i.e., zero lag) correlation between the optical and X-ray fluxes. If X-rays are produced by inverse-Compton scattering of relativistic electrons on some seed photons, the above results exclude that the observed optical photons are the seeds and/or that the relativistic electrons radiating via synchrotron in the optical band are responsible for the scattering to X-ray energies. We suggest that the X-rays are instead produced through the inverse-Compton process by electrons of lower energy, which radiate via synchrotron in the radio to millimeter wave bands and which scatter either on the synchrotron photons themselves or on external photons.

Grandi, P.↗

NASA capabilities roadmap: advanced telescopes and observatories

The NASA Advanced Telescopes and Observatories (ATO) Capability Roadmap addresses technologies necessary for NASA to enable future space telescopes and observatories collecting all electromagnetic bands, ranging from x-rays to millimeter waves, and including gravity-waves. It has derived capability priorities from current and developing Space Missions Directorate (SMD) strategic roadmaps and, where appropriate, has ensured their consistency with other NASA Strategic and Capability Roadmaps. Technology topics include optics; wavefront sensing and control and interferometry; distributed and advanced spacecraft systems; cryogenic and thermal control systems; large precision structure for observatories; and the infrastructure essential to future space telescopes and observatories.

Feinberg, Lee D.↗

High speed photography, videography, and photonics III; Proceedings of the Meeting, San Diego, CA, August 22, 23, 1985

Papers are presented on the picosecond electronic framing camera, photogrammetric techniques using high-speed cineradiography, picosecond semiconductor lasers for characterizing high-speed image shutters, the measurement of dynamic strain by high-speed moire photography, the fast framing camera with independent frame adjustments, design considerations for a data recording system, and nanosecond optical shutters. Consideration is given to boundary-layer transition detectors, holographic imaging, laser holographic interferometry in wind tunnels, heterodyne holographic interferometry, a multispectral video imaging and analysis system, a gated intensified camera, a charge-injection-device profile camera, a gated silicon-intensified-target streak tube and nanosecond-gated photoemissive shutter tubes. Topics discussed include high time-space resolved photography of lasers, time-resolved X-ray spectrographic instrumentation for laser studies, a time-resolving X-ray spectrometer, a femtosecond streak camera, streak tubes and cameras, and a short pulse X-ray diagnostic development facility.

Ponseggi, B. G.↗

Advanced Protein Crystallization Facility (APCF)

This section of the Life and Microgravity Spacelab (LMS) publication contains articles entitled: (1) Crystallization of EGFR-EGF; (2) Crystallization of Apocrustacyanin C1; (3) Crystallization and X-ray Analysis of 5S rRNA and the 5S rRNA Domain A; (4) Growth of Lysozyme Crystals at Low Nucleation Density; (5) Comparative Analysis of Aspartyl tRNA-synthetase and Thaumatin Crystals Grown on Earth and In Microgravity; (6) Lysosome Crystal Growth in the Advanced Protein Crystallization Facility Monitored via Mach-Zehnder Interferometry and CCD Video; (7) Analysis of Thaumatin Crystals Grown on Earth and in Microgravity; (8) Crystallization of the Nucleosome Core Particle; (9) Crystallization of Photosystem I; (10) Mechanism of Membrane Protein Crystal Growth: Bacteriorhodopsin-mixed Micelle Packing at the Consolution Boundary, Stabilized in Microgravity; (11) Crystallization in a Microgravity Environment of CcdB, a Protein Involved in the Control of Cell Death; and (12) Crystallization of Sulfolobus Solfataricus

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[Build and Demonstrate a X-Ray Interferometer and Build and Fly a High Resolution Telescope on a Sounding Rocket}

This report is written with eight months still go on the 36 month period of the grant. This grant, as originally proposed three years ago, was two pronged - to build and demonstrate a practical x-ray interferometer, and to build and fly a high resolution telescope on a sounding rocket. As we started into these projects, we received community feedback that led to our giving priority to the interferometer., The rocket would achieve O.2-arcsecond resolution that, while better, than that of Chandra, would, because of the limited signal of a sub-orbital flight, not be of substantially greater scientific use. The interferometry, on the other hand, shows the potential for many orders of magnitude improvement. For this reason we gave priority to the lab interferometry, and the building of the telescope lagged behind. With our new understanding (and practical demonstration) of how to build an interferometer, we changed the telescope design from spherical surfaces in the Kirkpatrick-Baez configuration, to an interferometer with resolution between .005 and .05 arcseconds.

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The nucleus of M81 - Simultaneous 2.3 and 8.3 GHz Mark III VLBI observations

Mark III very long baseline interferometry (VLBI) observations have been made of the nucleus in the normal galaxy M81 (NGC 3031) simultaneously at 2.3 and 8.3 GHz, and it was found that nearly 100% of the flux density of the nuclear region originates in an elongated radio core with linear dimensions 1000-4000 AU, dependent on frequency. This galactic nucleus is the most compact observed in any extragalactic source. The position coincides with that of the nucleus at optical and X-ray wavelengths within the larger uncertainties of the latter two. The position angle of the major axis of the M81 nucleus is within 3 deg of 75 deg at 2.3 GHz and within 6 deg of 50 deg at 8.3 GHz and is frequency dependent at the 4 sigma level. These values straddle the 62 deg position angle of the projection on the sky of the rotation axis of the galaxy. The spectrum of the core is slightly inverted, and the length of its major axis decreases with frequency. These results are consistent with the emission's being incoherent electron synchrotron radiation from an inhomogeneous region with an optical depth varying along the rotation axis of the galaxy.

Bartel, N.↗

Influence of the active nucleus on the multiphase interstellar medium in NGC 1068

The luminous spiral NGC 1068 has now been imaged from x-ray to radio wavelengths at comparably high resolution (approximately less than 5 in. FWHM). The bolometric luminosity of this well-known Seyfert is shared almost equally between the active nucleus and an extended 'starburst' disk. In an ongoing study, we are investigating the relative importance of the nucleus and the disk in powering the wide range of energetic activity observed throughout the galaxy. Our detailed analysis brings together a wealth of data: ROSAT HRI observations, VLA lambda lambda 6-20 cu cm and OVRO interferometry, lambda lambda 0.4-10.8 micron imaging, and Fabry-Perot spectrophotometry.

Bland-Hawthorn, Jonathan↗

NASA Laboratory Astrophysics Workshop 2006 Introductory Remarks

NASA Laboratory Astrophysics Workshop 2006, is the fourth in a series of workshops held at four year intervals, to assess the laboratory needs of NASA's astrophysics missions - past, current and future. Investigators who need laboratory data to interpret their observations from space missions, theorists and modelers, experimentalists who produce the data, and scientists who compile databases have an opportunity to exchange ideas and understand each other's needs and limitations. The multi-wavelength character of these workshops allows cross-fertilization of ideas, raises awareness in the scientific community of the rapid advances in other fields, and the challenges it faces in prioritizing its laboratory needs in a tight budget environment. Currently, we are in the golden age of Space Astronomy, with three of NASA s Great Observatories, Hubble Space Telescope (HST), Chandra X-Ray Observatory (CXO), and Spitzer Space Telescope (SST), in operation and providing astronomers and opportunity to perform synergistic observations. In addition, the Far Ultraviolet Spectroscopic Explorer (FUSE), XMM-Newton, HETE-2, Galaxy Evolution Explorer (GALEX), INTEGRAL and Wilkinson Microwave Anisotropy Probe (WMAP), are operating in an extended phase, while Swift and Suzaku are in their prime phase of operations. The wealth of data from these missions is stretching the Laboratory Astrophysics program to its limits. Missions in the future, which also need such data include the James Webb Space Telescope (JWST), Space Interferometry Mission (SIM), Constellation-X (Con-X), Herschel, and Planck. The interpretation of spectroscopic data from these missions requires knowledge of atomic and molecular parameters such as transition probabilities, f-values, oscillator strengths, excitation cross sections, collision strengths, which have either to be measured in the laboratory by simulating space plasma and interactions therein, or by theoretical calculations and modeling. Once the laboratory data are obtained, a key step to making them available to the observer is the creation and maintenance of critically compiled databases. Other areas of study, that are important for understanding planet formation, and for detection of molecules that are indicators of life, are also supported by the Laboratory Astrophysics program. Some examples are: studies of ices and dust grains in a space environment; nature and evolution of interstellar carbon-rich dust; and polycyclic aromatic hydrocarbons. In addition, the program provides an opportunity for the investigation of novel ideas, such as simulating radiative shock instabilities in plasmas, in order to understand jets observed in space. A snapshot of the currently funded program, mission needs, and relevance of laboratory data to interpreting observations, will be obtained at this workshop through invited and contributed talks and poster papers. These will form the basis for discussions in splinter groups. The Science Organization Committee will integrate the results of the discussions into a coherent White Paper, which will provide guidance to NASA in structuring the Laboratory Astrophysics program in subsequent years, and also to the scientific community in submitting research proposals to NASA for funding.

Hasan, Hashima↗

Measurement of Precision Geometric Distances to Three Anchor Points in the Local Universe

We proposed a program to measure distances directly with accuracies of 5% to three anchor points in the Local Universe. We planned to accomplish this by conducting Very Long Baseline Interferometry (VLBI) observations of NGC 4258, M 33, and Sgr A*. These distance estimates should have a minimum of systematic uncertainty and can be used to re-calibrate several 'standard candles,' such as Cepheid and RR Lyrae variables. This will place the Galactic and extragalactic distance scales on much firmer ground. The primary contribution of our program will be to provide crucial independent checks and calibrations of extragalactic distance measurements. This will contribute to the ultimate success and impact of the HST Key Project on Extragalactic Distances and the Full-Sky Astrometric Mapping Explorer (FAME). Additionally, since distances are fundamental to astrophysics, our results will affect a large number of general projects on NASA facilities such as the Hubble Space Telescope, Chandra X-ray Observatory, and Next Generation Space Telescope.

Reid, Mark J.↗

Measurement of Precision Geometric Distances to Three Anchor Points in the Local Universe

Our program, funded by a NASA/SARA 3-yr grant, is designed to measure distances directly with accuracies of 5% to three anchor points in the Local Universe. We are attacking this problem on three fronts, using Very Long Baseline Interferometry (VLBI) observations of NGC 4258, M 33, and Sgr A*. We plan to provide distance estimates, with a minimum of systematic uncertainty, that can be used to re-calibrate several 'standard candles,' such as Cepheid and RR Lyrae variables. This will place the Galactic and extragalactic distance scales on much firmer ground. The program will provide crucial, independent checks and calibrations of extragalactic distance measurements, and will contribute to the ultimate success and impact of the HST Key Project on Extragalactic Distances, the Full-Sky Astrometric Mapping Explorer (FAME), and any future NASA astrometric missions. Additionally, since distances are fundamental to astrophysics, our results will affect a large number of general projects on NASA facilities such as the HST (Hubble Space Telescope), CXO (Chandra X-Ray Observatory), and NGST (Next Generation Space Telescope).

Reid, Mark J.↗

Spatially Resolved Imaging at 350 Micrometers of Cold Dust in Nearby Elliptical Galaxies

Continuum observations at 350 micrometers of seven nearby elliptical galaxies for which CO gas disks have recently been resolved with interferometry mapping are presented. These SHARC II mapping results provide the first clearly resolved far-infrared (FIR)-to-submillimeter continuum emission from cold dust (with temperatures 31 K is approximately greater than T approximately greater than 23 K) of any elliptical galaxy at a distance greater than 40 Mpc. The measured FIR excess shows that the most likely and dominant heating source of this dust is not dilute stellar radiation or cooling flows, but rather star formation that could have been triggered by an accretion or merger event and fueled by dust-rich material that has settled in a dense region cospatial with the central CO gas disks. The dust is detected even in two cluster ellipticals that are deficient in H (sub I), showing that, unlike H (sub I), cold dust and CO in ellipticals can survive in the presence of hot X-ray gas, even in galaxy clusters. No dust cooler than 20 K, either distributed outside the CO disks or cospatial with and heated by the entire dilute stellar optical galaxy (or very extended H (sub I)), is currently evident.

photometry↗

High dynamic range radio observations of PKS 1413+135: A BL Lacertae object with a parsec-scale counterjet

We report the results of three high dynamic range, high-resolution radio observations with the Very Large Array (VLA), US Very Long Base Interferometry (VLBI) Network, and partially completed Very Long Baseline Array (VLBA) on the peculiar BL Lacertae objects PKS 1413+135. The VLA observations (resolution approximately 1.5 sec) reveal that PKS 1413+135 has no kiloparsec-scale extended structure to a dynamic range limit of 10,000:1. However, its milliarcsecond-scale structure appears to be a triple (i.e., a core, jet plus 'counterjet') at both 3.6 and 18 cm, a unique structure among BL Lac objects but similar to a recently discovered class of VLBI 'mini-triples.' The presence of a counterjet at fluxes comparable to the main jet is incompatible with the standard relativistically beamed jet model for BL Lac objects and with the high value of core dominance exhibited by this source at arcsec resolution. This suggests a nonstandard interpretation in which the radio source lies far in the background of the spiral galaxy it is projected upon so that its VLBI structure may be affected by gravitational lensing. At 18 cm, the core is much weaker than at 3.6 cm suggesting free-free absorption by the high-column-density gas found along this sightline by previous infrared(IR)/optical, X-ray and redshifted H I 21 cm observations. We discuss the roles that free-free absorption and gravitational lensing may have for PKS 1413+135 and other GHz-peaked spectrum radio sources.

Perlman, Eric S.↗

Holographic Optical Data Storage

Although the basic idea may be traced back to the earlier X-ray diffraction studies of Sir W. L. Bragg, the holographic method as we know it was invented by D. Gabor in 1948 as a two-step lensless imaging technique to enhance the resolution of electron microscopy, for which he received the 1971 Nobel Prize in physics. The distinctive feature of holography is the recording of the object phase variations that carry the depth information, which is lost in conventional photography where only the intensity (= squared amplitude) distribution of an object is captured. Since all photosensitive media necessarily respond to the intensity incident upon them, an ingenious way had to be found to convert object phase into intensity variations, and Gabor achieved this by introducing a coherent reference wave along with the object wave during exposure. Gabor's in-line recording scheme, however, required the object in question to be largely transmissive, and could provide only marginal image quality due to unwanted terms simultaneously reconstructed along with the desired wavefront. Further handicapped by the lack of a strong coherent light source, optical holography thus seemed fated to remain just another scientific curiosity, until the field was revolutionized in the early 1960s by some major breakthroughs: the proposition and demonstration of the laser principle, the introduction of off-axis holography, and the invention of volume holography. Consequently, the remainder of that decade saw an exponential growth in research on theory, practice, and applications of holography. Today, holography not only boasts a wide variety of scientific and technical applications (e.g., holographic interferometry for strain, vibration, and flow analysis, microscopy and high-resolution imagery, imaging through distorting media, optical interconnects, holographic optical elements, optical neural networks, three-dimensional displays, data storage, etc.), but has become a prominent am advertising, and security medium as well. The evolution of holographic optical memories has followed a path not altogether different from holography itself, with several cycles of alternating interest over the past four decades. P. J. van Heerden is widely credited for being the first to elucidate the principles behind holographic data storage in a 1963 paper, predicting bit storage densities on the order of 1/lambda(sup 3) with source wavelength lambda - a fantastic capacity of nearly 1 TB/cu cm for visible light! The science and engineering of such a storage paradigm was heavily pursued thereafter, resulting in many novel hologram multiplexing techniques for dense data storage, as well as important advances in holographic recording materials. Ultimately, however, the lack of such enabling technologies as compact laser sources and high performance optical data I/O devices dampened the hopes for the development of a commercial product. After a period of relative dormancy, successful applications of holography in other arenas sparked a renewed interest in holographic data storage in the late 1980s and the early 1990s. Currently, with most of the critical optoelectronic device technologies in place and the quest for an ideal holographic recording medium intensified, holography is once again considered as one of several future data storage paradigms that may answer our constantly growing need for higher-capacity and faster-access memories.

Timucin, Dogan A.↗

Very long baseline interferometry observations of the RS Canum Venaticorum system HR 5110 at 8.4 GHz

The RS CVn binary system HR 5110 was observed with a well-calibrated four-element VLBI array at a frequency of 8.4 GHz. The total flux density, which was nearly constant at 32 + or - 2 mJy, was monitored throughout the experiment with a 20 km baseline interferometer allowing accurate visibilities to be calculated. The observed visibilities are consistent with a source unresolved on all the baselines. The maximum size of the equivalent Gaussian source is 1.4 milli-arcsec (FWHM), corresponding to a linear size of 1.1 x 10 to the 12th cm at 52 pc. This maximum size is comparable with the overall size of the binary system. The inferred lower limit of the brightness temperature is 4 x 10 to the 8th K, which is higher than the coronal temperature of 10 to the 7th K measured in a soft X-ray survey. This is consistent with a nonthermal mechanism for the radiation process of the moderate radio outburst observed.

Mutel, R. L.↗

NASA astrophysics - Optical systems to explore the universe

Major and minor NASA astrophysical research efforts in the near-term are outlined, together with projections of direction for future projects. The Space Telescope is being readied for a 1986 launch and will feature an f/24, 2.4 m aperture, an MgF2 mirror with better than 1/60 wavelength accuracy and will be diffraction-limited in the UV. Pointing accuracy is designed to be 0.007 arcsec for 24 hr. Optical, spectrometric, and photometric equipment will be included. Around 1990, Shuttle-based missions will include an IR telescope and a subarcsec solar surface imaging device. A free-flying X-ray observatory (AXAF) is planned and will include a sensitivity that exceeds that of the HEAO-2 spacecraft by two orders of magnitude. Instruments are under development for higher resolution UV, gamma-ray, and IR studies. In-orbit interferometry is being studied and will depend on in-orbit assembly and servicing of stable structures with segmented optics.

Pellerin, C. J., Jr.↗

High Resolution X-ray Imaging

Improved image quality is of central importance to the future of X ray astronomy. We show that the optical tolerances necessary to push the quality of grazing incidence telescopes well beyond their current one arcsecond limit, are achievable. We also discuss a new approach to X ray optics that has been under development and is already showing resolution as high a 0.1 arcseconds. We argue that diffraction limited resolution should be considered as a viable goal for a new start among the next generation observatories, and follow the line of reasoning into X ray interferometry as a long term goal.

Cash, Webster↗