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  • Other Sources  (29)
  • Astrophysics  (29)
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  • Surface physics, nanoscale physics, low-dimensional systems
  • 2015-2019  (29)
  • 1995-1999
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  • 2015  (29)
  • 1
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    Feedhorn-Coupled Transition-Edge Superconducting Bolometer Arrays for Cosmic Microwave Background Polarimetry (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NIST produces large-format, dual-polarization-sensitive detector arrays for a broad range of frequencies (30-1400 GHz). Such arrays enable a host of astrophysical measurements. Detectors optimized for cosmic microwave background observations are monolithic, polarization-sensitive arrays based on feedhorn and planar Nb antenna-coupled transition-edge superconducting (TES) bolometers. Recent designs achieve multiband, polarimetric sensing within each spatial pixel. In this proceeding, we describe our multichroic, feedhorn-coupled design; demonstrate performance at 70-380 GHz; and comment on current developments for implementation of these detector arrays in the advanced Atacama Cosmology Telescope receiver
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN32074 , International Symposium on Space Terahertz Technology; Mar 16, 2015 - Mar 18, 2015; Cambridge, MA; United States
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  • 2
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    Cosmology Large Angular Scale Surveyor (CLASS) Focal Plane Development (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization of the Cosmic Microwave Background to search for and characterize the polarized signature of inflation. CLASS will operate from the Atacama Desert and observe approx.70% of the sky. A variable-delay polarization modulator provides modulation of the polarization at approx.10Hz to suppress the 1/f noise of the atmosphere and enable the measurement of the large angular scale polarization modes. The measurement of the inflationary signal across angular scales that spans both the recombination and reionization features allows a test of the predicted shape of the polarized angular power spectra in addition to a measurement of the energy scale of inflation. CLASS is an array of telescopes covering frequencies of 38, 93, 148, and 217 GHz. These frequencies straddle the foreground minimum and thus allow the extraction of foregrounds from the primordial signal. Each focal plane contains feedhorn-coupled transition-edge sensors that simultaneously detect two orthogonal linear polarizations. The use of single-crystal silicon as the dielectric for the on-chip transmission lines enables both high efficiency and uniformity in fabrication. Integrated band definition has been implemented that both controls the bandpass of the single-mode transmission on the chip and prevents stray light from coupling to the detectors.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN32347 , Journal of Low Temperature Physics (e-ISSN 1573-7357); 1-6
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  • 3
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    Beyond Chandra -The X-Ray Surveyor The Future for High-Resolution X-Ray Astronomy (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Astrophysics
    Type: MSFC-E-DAA-TN22442 , SPIE Optics and Optoelectronics Conference; Apr 13, 2015 - Apr 16, 2015; Prague; Czechoslovakia
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  • 4
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    First Measurement of the Cross-Correlation of CMB Lensing and Galaxy Lensing (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We measure the cross-correlation of cosmic microwave background (CMB) lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 4.2, which corresponds to a 12% constraint on the amplitude of density fluctuations at redshifts 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN22729 , Physical Review D (ISSN 2470-0010) (e-ISSN 2470-0029); 91; 6; 062001
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  • 5
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    Unveiling the Secrets of Metallicity and Massive Star Formation Using DLAs Along Gamma-Ray Bursts (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present the largest, publicly available, sample of Damped Lyman-alpha systems (DLAs) along Swift discovered Gamma-ray Bursts (GRB) line of sights in order to investigate the environmental properties of long GRB hosts in the z = 1.8 6 redshift range. Compared with the most recent quasar DLAs sample (QSO-DLA), our analysis shows that GRB-DLAs probe a more metal enriched environment at z approximately greater than 3, up to [X/H] approximately 0.5. In the z = 2 3 redshift range, despite the large number of lower limits, there are hints that the two populations may be more similar (only at 90% significance level) than at higher redshifts. Also, at high-z, the GRB-DLA average metallicity seems to decline at a shallower rate than the QSO-DLAs: GRB-DLA hosts may be polluted with metals at least as far as approximately 2 kpc from the GRB explosion site, probably due to previous star-formation episodes and/or supernovae explosions. This shallow metallicity trend, extended now up to z approximately 5, confirms previous results that GRB hosts are star-forming and have, on average, higher metallicity than the general QSO-DLA population. Finally, our host metallicity measurements are broadly consistent with the predictions derived from the hypothesis of two channels of GRB progenitors, one of which is mildly affected by a metallicity bias, although more data are needed to constrain the models at z approximately greater than 4.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN21332 , The Astrophysical Journal (e-ISSN 2041-8213); 804; 1; 51
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  • 6
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    Determining the Covering Factor of Compton-Thick Active Galactic Nuclei with NuSTAR (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The covering factor of Compton-thick (CT) obscuring material associated with the torus in active galactic nuclei (AGNs) is at present best understood through the fraction of sources exhibiting CT absorption along the line of sight (N(sub H) greater than 1.5 x 10(exp 24) cm(exp 2)) in the X-ray band, which reveals the average covering factor. Determining this CT fraction is difficult, however, due to the extreme obscuration. With its spectral coverage at hard X-rays (greater than 10 keV), Nuclear Spectroscopic Telescope Array (NuSTAR) is sensitive to the AGNs covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGNs observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so-called CT AGNs. We use the torus models of Brightman and Nandra that predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the CT gas in these sources individually. Across the sample we find mild to heavy CT columns, with N(sub H) measured from 10(exp 24) to 10(exp 26) cm(exp 2), and a wide range of covering factors, where individual measurements range from 0.2 to 0.9. We find that the covering factor, f(sub c), is a strongly decreasing function of the intrinsic 2-10 keV luminosity, L(sub X), where f(sub c) = (0.41 +/- 0.13)log(sub 10)(L(sub X)/erg s(exp 1))+18.31 +/- 5.33, across more than two orders of magnitude in L(sub X) (10(exp 41.5) - 10(exp 44) erg s(exp 1)). The covering factors measured here agree well with the obscured fraction as a function of LX as determined by studies of local AGNs with L(sub X) greater than 10(exp 42.5) erg s(exp 1).
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN35028 , The Astrophysical Journal; 805; 1; 41
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  • 7
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    Ti-44 Gamma-Ray Emission Lines from SN1987A Reveal an Asymmetric Explosion (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In core-collapse supernovae, titanium-44 (Ti-44) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of Ti-44 produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN34983 , Science Magazine (e-ISSN 1095-9203); 348; 6235; 670-671
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  • 8
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    Neon and Helium in the Surface of Stardust Cell C2028 (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Previous studies of light noble gases in Stardust aerogel samples detected a variety of isotopically non-terrestrial He and Ne compositions. However, with one exception, in none of these samples was there visible evidence for the presence of particles that could have hosted the gases. The exception is materials keystoned from track 41, cell C2044, which contained observable fragments of the impacting Wild 2 comet coma grain. Here we report noble gas data from a second aerogel sample in which grains are observed, cut from the surface of a cell (C2028) riddled with tiny tracks and particles that are thought to be secondary in origin, ejected toward the cell when a parent grain collided with the spacecraft structure and fragmented. Interestingly, measured 20Ne/22Ne ratios in the track 41 and C2028 samples are similar, and within error of the meteoritic "Q-phase" Ne composition.
    Keywords: Astrophysics
    Type: JSC-CN-32883 , Lunar and Planetary Science Conference; Mar 16, 2015 - Mar 20, 2015; The Woodlands, TX; United States
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  • 9
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    Detailed Structure of the Outer Disk Around HD 169142 with Polarized Light in H-band (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2r1.2, or 29r174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 2952 AU and r = 81.2145 AU respectively show r3-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 4070 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner power-law region (r 〈50 AU) is derived to be 0.16 from a simple model calculation. The obtained PI image also shows small scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and shadowing effect by a puffed up structure in the inner power-law region.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN33497 , Publications of the Astronomical Society of Japan (e-ISSN 2053-051X); 67; 5; 1-26
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  • 10
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    Evidence for a Dynamic Nanodust Cloud Enveloping the Moon (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The exospheres that surround airless bodies such as the Moon are tenuous, atmosphere-like layers whose constituent particles rarely collide with one another. Some particles contained within such exospheres are the product of direct interactions between airless bodies and the space environment, and offer insights into space weathering processes. NASAs Lunar Atmosphere and Dust Environment Explorer (LADEE) mission studied the Moons exospheric constituents in situ and detected a permanent dust exosphere1 of particles with radii as small as 300 nm. Here we present evidence from LADEE spectral data for an additional fluctuating nanodust exosphere at the Moon containing a population of particles sufficiently dense to be detectable via scattered sunlight. We compare two anti-Sun spectral observations: one near the peak of the Quadrantidmeteoroid stream, the other during a period of comparativelyweak stream activity. The former shows a negative spectralslope consistent with backscattering of sunlight by nanodustgrains with radii less than 20 to 30 nm; the latter has a flatterspectral slope. We hypothesize that a spatially and temporallyvariable nanodust exosphere may exist at the Moon, and thatit is modulated by changes in meteoroid impact rates, suchas during encounters with meteoroid streams. The findingssuggest that similar nanodust exospheresand the particle ejection and transport processes that form themmay occurat other airless bodies.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN40230 , Nature Geoscience (ISSN 1752-0894) (e-ISSN 1752-0908); 9; 9; 665-668
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