Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “imaging arrays”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The X-shaped Radio Galaxy J0725+5835 is Associated with an AGN Pair

X-shaped radio galaxies (XRGs) are those that exhibit two pairs of unaligned radio lobes (main radio lobes and wings). One of the promising models for the peculiar morphology is jet reorientation. To clarify this, we conducted a 5 GHz observation with the European VLBI Network (EVN) of XRG J0725+5835, which resembles the archetypal binary active galactic nuclei (AGNs) 0402+379 in radio morphology, but it is larger in angular size. In our observation, two milliarcsecond-scale radio components with nonthermal radio emission are detected. Each of them coincides with an optical counterpart with similar photometric redshift and (optical and infrared) magnitude, corresponding to dual active nuclei. Furthermore, with the improved Very Large Array (VLA) images, we find a bridge between the two radio cores and a jet bending in the region surrounding the companion galaxy. This further supports the interplay between the main and companion galaxies. In addition, we also report the discovery of an arcsecond-scale jet in the companion. Given the projected separation of ~100 kpc between the main and companion galaxies, XRG J0725+5835 is likely associated with a dual jetted-AGN system. In both EVN and VLA observations, we find signatures that the jet is changing its direction, which is likely responsible for the X-shaped morphology. For the origin of jet reorientation, several scenarios are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

VERITAS Discovery of Very High Energy Gamma-Ray Emission from S3 1227+25 and Multiwavelength Observations

We report the detection of very high energy gamma-ray emission from the blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). VERITAS observations of the source were triggered by the detection of a hard-spectrum GeV flare on 2015 May 15 with the Fermi-Large Area Telescope (LAT). A combined 5 hr VERITAS exposure on May 16 and 18 resulted in a strong 13σ detection with a differential photon spectral index, Γ = 3.8 ± 0.4, and a flux level at 9% of the Crab Nebula above 120 GeV. This also triggered target-of-opportunity observations with Swift, optical photometry, polarimetry, and radio measurements, also presented in this work, in addition to the VERITAS and Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period finds evidence of a shortest variability timescale of τ obs = 6.2 ± 0.9 hr, indicating emission from compact regions within the jet, and the combined gamma-ray spectrum shows no strong evidence of a spectral cutoff. An investigation into correlations between the multiwavelength observations found evidence of optical and gamma-ray correlations, suggesting a single-zone model of emission. Finally, the multiwavelength spectral energy distribution is well described by a simple one-zone leptonic synchrotron self-Compton radiation model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Multiwavelength Investigation of γ-Ray Source MGRO J1908+06 Emission Using Fermi-LAT, VERITAS and HAWC

This paper investigates the origin of the γ-ray emission from MGRO J1908+06 in the GeV–TeV energy band. By analyzing the data collected by the Fermi Large Area Telescope, the Very Energetic Radiation Imaging Telescope Array System, and High Altitude Water Cherenkov, with the addition of spectral data previously reported by LHAASO, a multiwavelength study of the morphological and spectral features of MGRO J1908+06 provides insight into the origin of the γ-ray emission. The mechanism behind the bright TeV emission is studied by constraining the magnetic field strength, the source age, and the distance through detailed broadband modeling. Both spectral shape and energy-dependent morphology support the scenario that inverse Compton emission of an evolved pulsar wind nebula associated with PSR J1907+0602 is responsible for the MGRO J1908+06 γ-ray emission with a best-fit true age of T = 22 ± 9 kyr and a magnetic field of B = 5.4 ± 0.8 μG, assuming the distance to the pulsar d PSR = 3.2 kpc.

Gamma-ray astronomy↗
DOE OSTI2026

VERITAS Observations Contemporaneous with the LHAASO Detection of NGC 4278

Significant gamma-ray emission between 1 TeV and 20 TeV from a point source, 1LHAASO J1219+2915, consistent with the location of the LINER/LLAGN galaxy NGC 4278 was recently reported by the Large High Altitude Air Shower Observatory (LHAASO) collaboration. These data were later split into active and quasi-quiet states, with most of the LHAASO significance coming from the active state (MJD 59449-59589). Subsequent analysis of Fermi-LAT and Swift-XRT observations have been used to explore the double-peaked broadband emission. Models of the spectral energy distribution (SED) are currently unconstrained due to the lack of contemporaneous multiwavelength data at either peak. Here, we report serendipitous observations of NGC 4278 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS), made possible by the contemporaneous observations of the nearby blazars 1ES 1218+304, 1ES 1215+303, and W Comae, each of which are located within 2° of NGC 4278. VERITAS did not detect any gamma-ray emission, and a flux upper limit was calculated. The flux upper limits constrain the photon spectrum of the quasi-quiet period, and together with Fermi-LAT, indicate a peak in the SED between 100 GeV and 2 TeV. We present an interpretation of the broadband SED that is based on acceleration of protons in the corona of the active galactic nuclei, followed by p–γ interactions and optically thin γ-ray emission. Within this framework, the implied neutrino signal is slightly below the current sensitivity of IceCube.

Archer, A. [DePauw University, Greencastle, IN (Un↗
NASA NTRS1972

Advances in pyroelectric infrared detectors.

Recent improvements in the pyroelectric detector have been due to the development of locked-in polarization, further reduction of the FET leakage current, and reduction of short circuit noise. The pyroelectric detector has been successfully employed in these typical applications: (1) thermograph using a single detector and X-Y scanner, (2) focal plane reticle scanner, (3) linear array thermal imaging system, (4) pyroelectric image tube, (5) radiometers (vertical temperature profile radiometer, carbon dioxide sensor), (6) high speed spectrometer, and (7) laser detector.

Beerman, H. P.↗
NASA NTRS1976

Architecture and data processing alternatives for the TSE computer. Volume 3: Execution of a parallel counting algorithm using array logic (Tse) devices

A parallel algorithm for counting the number of logic-l elements in a binary array or image developed during preliminary investigation of the Tse concept is described. The counting algorithm is implemented using a basic combinational structure. Modifications which improve the efficiency of the basic structure are also presented. A programmable Tse computer structure is proposed, along with a hardware control unit, Tse instruction set, and software program for execution of the counting algorithm. Finally, a comparison is made between the different structures in terms of their more important characteristics.

Metcalfe, A. G.↗
NASA NTRS1983

Spectral consequences of photoreceptor sampling in the rhesus retina

Optical transforms were used to compute the power spectra of rhesus cones treated as arrays of image sampling points. Spectra were obtained for the central fovea, parafovea, periphery, and far periphery. All were consistent with a novel spatial sampling principle that introduces minimal noise for spatial frequencies below the Nyquist limits implied by local receptor densities, while frequencies above the nominal Nyquist limits are not converted into conspicuous moiree patterns, but instead are scattered into broadband noise. This sampling scheme allows the visual system to escape aliasing distortion despite a large mismatch between retinal image bandwidth and the Nyquist limits implied by extrafoveal cone densities.

Yellott, J. I., Jr.↗
NASA NTRS1984

A preliminary analysis of a diode array for densitometry

A diode-array based image digitizer manufactured by the Eikonix Corp. was tested to see if it can be adapted to the exacting requirements of astronomical densitometry. As the device is presently configured, a dynamic range of 400:1 can be achieved routinely, with a positional accuracy of 2 microns or better. An area of 2048 X 2048 pixels can be scanned in about 5 minutes. Preliminary tests indicate that several relatively simple enhancements can improve both the photometric and the positional accuracy of the device.

Janes, K. A.↗
NASA NTRS1985

An intensified photodiode array detector for space applications

The Hopkins Ultraviolet Telescope (HUT) is a general purpose moderate resolution spectrograph which is now being constructed for launch on the Space Shuttle. The instrument contains a Rowland spectrograph, which is located at the prime focus of a 0.9-m f/2 parabola. A description is given of the progress which has been made in the development of a flight detector for HUT. The detector developed is an intensified photodiode array. The image intensifier part of the detector contains two 25-mm 80:1, 12-micron pore microchannel plates (PCPs). A thin layer of CsI deposited on the front surface of the first microchannel plate has the objective to increase the quantum efficiency of the detector below 1850 A. The detector system utilizes a spectrometer processor (SP) which is based upon a bit-sliced microprocessor. The current status of the HUT detector system is discussed, and aspects of performance are evaluated. It is felt that the developed system will meet or exceed the design requirements.

Long, K. S.↗
NASA NTRS1987

Structure in the nucleus of NGC 1068 at 10 microns

New 8 to 13 micron array camera images of the central kiloparsec of Seyfert 2 galaxy NGC 1068 resolve structure that is similar to that observed at visible and radio wavelengths. The images reveal an infrared source which is extended and asymmetric, with its long axis oriented at P.A. 33 deg. Maps of the spatial distribution of 8 to 13 micron color temperature and warm dust opacity are derived from the multiwavelength infrared images. The results suggest that there exist two pointlike luminosity sources in the central regions of NGC 1068, with the brighter source at the nucleus and the fainter one some 100 pc to the northeast. This geometry strengthens the possibility that the 10 micron emission observed from grains in the nucleus is powered by a nonthermal source. In the context of earlier visible and radio studies, these results considerably strengthen the case for jet induced star formation in NGC 1068.

Tresch-Fienberg, R.↗
NASA NTRS1987

Structure in the nucleus of NGC 1068 at 10 microns

New 8-13 micron array camera images of the central kiloparsec of Seyfert 2 galaxy NGC 1068 resolve structure that is similar to that observed at visible and radio wavelengths. The images reveal an infrared source which is extended and asymmetric, with its long axis oriented at P.A. 33 deg. Maps of the spatial distribution of 8-13 micron color temperature and warm dust opacity are derived from the multiwavelength infrared images. The results suggest that there exist two pointlike luminosity sources in the central region of NGC 1068, with the brighter source at the nucleus and the fainter one some 100 pc to the northeast. This geometry strengthens the possibility that the 10 micron emission observed from grains in the nucleus is powered by a nonthermal source. In the context of earlier visible and radio studies, these results considerably strengthen the case for jet-induced star formation in NGC 1068.

Tresch-Fienberg, R.↗
NASA NTRS1987

Matching a curved focal plane with CCD's - Wide field imaging of glancing incidence X-ray telescopes

The design of a wide field imaging camera suitable for use with a glancing incidence X-ray telescope is complicated by the sharply concave nature of the optimum focal surface of such a telescope. Such a camera made up of a mosaic of CCDs is being designed which is intended for flight aboard the Advanced X-ray Astrophysics Facility (AXAF). The design rationale and tradeoffs are discussed, and the layout for the imaging CCD array is presented. The related issue of optimizing performance of transmission objective gratings is also discussed, and the array of CCD orientations suitable for this problem is presented.

Nousek, J. A.↗
NASA NTRS1989

Optical multiple object tracking techniques

Two multichannel multiple-object tracking techniques are reviewed. In the diffraction grating technique, the input scene is picked up by a TV camera and imaged onto a liquid-crystal light valve (LCLV), and the output side of the light valve is illuminated with a suitably polarized and collimated coherent laser beam to yield a reflected beam with polarization modulated according to the intensity of the incoherent input. This reflected beam passes through a beam splitter cube and an analyzer, resulting in an intensity modulated coherent image. An array of spectrum islands containing the information of the input appears after crossing a contact screen/lens combination. In the multiple-focus hololens technique, the scene of moving objects is sent into the LCTVSLM through a camera; a collimated laser beam is incident upon the LCTV screen; a low-pass filter is inserted between the LCTVSLM and the hololens for the removal of the high order diffractions due to the grid structure of the LCTV. The feasibility of the LCTVSLM and multiple-focus hololens technique is demonstrated.

Liu, Hua-Kuang↗
NASA NTRS1989

Endfire tapered slot antenna characteristics

Typical configurations and operating characteristics for endfire tapered slot antennas are described. The feed transition modeling and moment method modeling techniques are utilized to predict antenna performance. The radiation pattern and cross polarization properties for the linearly tapered slot antennas are examined. Endfire tapered slot antennas are applicable for wide-band scanning arrays and focal plane arrays for imaging and multiple beam reflector systems.

Schaubert, D. H.↗
NASA NTRS1989

Reconstructing irregularly sampled images by neural networks

Neural-network-like models of receptor position learning and interpolation function learning are being developed as models of how the human nervous system might handle the problems of keeping track of the receptor positions and interpolating the image between receptors. These models may also be of interest to designers of image processing systems desiring the advantages of a retina-like image sampling array.

Ahumada, Albert J., Jr.↗
NASA NTRS1990

Issues and directions in IR detector readout electronics

An introduction to the major issues encountered in the readout of imaging detector arrays in the infrared are presented. These include circuit issues such as multiplexing, buffering, and noise, as well as materials issues. Future directions in infrared readout electronics will also be discussed. These include on-chip signal processing and advanced hybridization schemes. Finally, recent work at Columbia on 2DEG-charge coupled devices for IR detector multiplexing are described.

Fossum, Eric R.↗