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  • Astrophysics  (148)
  • 2015-2019  (148)
  • 2019  (148)
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  • 2015-2019  (148)
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  • 1
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    Binary Black Hole Growth by Gas Accretion in Stellar Clusters (2019)
    In:  CASI
    Details
    Publication Date: 2020-01-15
    Description: We show that binaries of stellar-mass black holes formed inside a young protoglobular cluster, can grow rapidly inside the clusters core by accretion of the intracluster gas, before the gas may be depleted from the core. A black hole with mass of the order of eight solar masses can grow to values of the order of thirty five solar masses in accordance with recent gravitational waves signals observed by LIGO. Due to the black hole mass increase, a binary may also harden. The growth of binary black holes in a dense protoglobular cluster through mass accretion indicates a potentially important formation and hardening channel.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN67184 , Astronomy & Astrophysics (ISSN 0004-6361) (e-ISSN 1432-0746); 621; L1
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  • 2
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    NICER Observation of Unusual Burst Oscillations in 4U 1728-34 (2019)
    In:  Other Sources
    Details
    Publication Date: 2020-01-15
    Description: The Neutron Star Interior Composition Explorer has observed seven thermonuclear X-ray bursts from the lowmass X-ray binary neutron star 4U 1728-34 from the start of the missions operations until 2019 February. Three of these bursts show oscillations in their decaying tail, with frequencies that are within 1 Hz of the previously detected burst oscillations from this source. Two of these burst oscillations have unusual properties: they have large fractional root mean square (rms) amplitudes of 48% 9% and 46% 9%, and they are detected only at photon energies above 6 keV. By contrast, the third detected burst oscillation is compatible with previous observations of this source, with a fractional rms amplitude of 7.7% 1.5% rms in the 0.3 to 6.2 keV energy band. We discuss the implications of these large-amplitude burst oscillations, finding that they are difficult to explain with the current theoretical models for X-ray burst tail oscillations.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN75255 , Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 878; 2; 145
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  • 3
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    Expanding the Sample of Radio Minihalos in Galaxy Clusters (2019)
    In:  Other Sources
    Details
    Publication Date: 2020-01-15
    Description: Radio minihalos are diffuse synchrotron sources of unknown origin found in the cool cores of some galaxy clusters. We use GMRT and VLA data to expand the sample of minihalos by reporting three new minihalo detections (A2667, A907, and PSZ1 G139.61+24.20) and confirming minihalos in five clusters (MACS J0159.80849, MACS J0329.60211, RXC J2129.6+0005, AS 780, and A3444). With these new detections and confirmations, the sample now stands at 23, the largest sample to date. For consistency, we also reanalyze archival VLA 1.4 GHz observations of seven known minihalos. We revisit possible correlations between the nonthermal emission and the thermal properties of their cluster hosts. Consistent with our earlier findings from a smaller sample, we find no strong relation between the minihalo radio luminosity and the total cluster mass. Instead, we find a strong positive correlation between the minihalo radio power and X-ray bolometric luminosity of the cool core (r 〈 70 kpc). This supplements our earlier result that most, if not all, cool cores in massive clusters contain a minihalo. Comparison of radio and Chandra X-ray images indicates that the minihalo emission is typically confined by concentric sloshing cold fronts in the cores of most of our clusters, supporting the hypothesis that minihalos arise from electron reacceleration by turbulence caused by core gas sloshing. Taken together, our findings suggest that the origin of minihalos should be closely related to the properties of thermal plasma in cluster cool cores.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN75253 , Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 880; 2; 70
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  • 4
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    Status of the Astronomical Rotengen Telescope - X-Ray Concentrator (ART-XC) (2019)
    In:  CASI
    Details
    Publication Date: 2020-01-04
    Description: No abstract available
    Keywords: Astrophysics
    Type: M19-7728 , Annual Mirror Technology Workshop; Nov 05, 2019 - Nov 08, 2019; Redondo Beach, CA; United States
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  • 5
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    Lynx X-Ray Observatory: Response to the First Astro 2020 Decadal Survey Request for Information (2019)
    In:  CASI
    Details
    Publication Date: 2020-01-03
    Description: This document serves as the Lynx Teams response to the first Request For Information (RFI) from the 2020 Decadal Survey in Astronomy and Astrophysics. Detailed answers to all of the questions asked in this RFI can be found in the Lynx Concept Study Report, Supplementary Technology Roadmaps, and the Lynx Cost Book.
    Keywords: Astrophysics
    Type: MSFC-E-DAA-TN76248
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  • 6
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    The NANOGrav 11 Yr Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries (2019)
    In:  Other Sources
    Details
    Publication Date: 2019-12-31
    Description: Observations indicate that nearly all galaxies contain supermassive black holes at their centers. When galaxies merge, their component black holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays. We have searched the North American Nanohertz Observatory for Gravitational Waves 11 yr data set for GWs from individual SMBHBs in circular orbits. As we did not find strong evidence for GWs in our data, we placed 95% upper limits on the strength of GWs from such sources. At f(gw) = 8 nHz, we placed a sky-averaged upper limit of h(0) 〈 7.3(3) 10(exp 15). We also developed a technique to determine the significance of a particular signal in each pulsar using "dropout" parameters as a way of identifying spurious signals. From these upper limits, we ruled out SMBHBs emitting GWs f(gw) = 8 nHz within 120 Mpc for M = 10(exp 9) Solar Mass, and within 5.5 Gpc for M= 10(exp 10) Solar Mass at our most sensitive sky location. We also determined that there are no SMBHBs with M 〉 1.6 x 10(exp 9) Solar Mass emitting GWs with f(gw) = 2.8317.8 nHz in the Virgo Cluster. Finally, we compared our strain upper limits to simulated populations of SMBHBs, based on galaxies in the Two Micron All-Sky Survey and merger rates from the Illustris cosmological simulation project, and found that only 34 out of 75,000 realizations of the local universe contained a detectable source.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN76492 , Astrophysical Journal; 880; 2; 116
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  • 7
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    The Changing Changing-Look AGN 1ES 1927+654 (2019)
    In:  CASI
    Details
    Publication Date: 2019-12-27
    Description: We report on X-ray follow-up observations of the March 2018 nuclear transient event AT2018zf (ASASSN-18el) from an ongoing campaign that includes XMM-Newton, NuSTAR, Swift, and high cadence (daily-to-weekly) NICER observations. The event was associated with the Seyfert galaxy 1ES 1927+654, a "True Type-2" that, nevertheless, showed an X-ray spectrum typical of an unobscured Type 1 AGN. Optical monitoring revealed the emergence of broad Balmer emission lines following the outburst, suggesting a transition from a Type 2 to a Type 1 AGN on timescales consistent with the light-travel time between the central black hole and the broad line region. The optical outburst was followed by a dramatic shift in the X-ray spectrum as the hard X-ray luminosity of the corona plunged by 〉2 orders of magnitude and the spectrum became dominated by a 10^6 K thermal component. The subsequent X-ray evolution of 1ES 1927+654 includes an additional two-order of magnitude decline in overall luminosity, followed by an extended period of quiescence, and re-brightening to levels that make it the brightest AGN currently in the X-ray sky. Throughout its evolution, the source has displayed X-ray flux variability of factors of several on timescales less than hour, and of ~100 on timescales less than a day. The X-ray spectrum varies along a consistent luminosity-dependent track, wherein increases in flux are accompanied by a spectral hardening. We seem to be witnessing the onset of an instability in the pre-existing AGN disc and corona, followed by a still-continuing re-emergence of the corona. If the initial transient is identified as the tidal disruption of a star, it is possible that this was the instigator of this unique behavior.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN75388 , The New Faces of Black Holes; Nov 11, 2019 - Nov 13, 2019; Annaplois, MD; United States
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  • 8
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    Multiabsorber Transition-Edge Sensors for X-Ray Astronomy (2019)
    In:  CASI
    Details
    Publication Date: 2019-12-27
    Description: We are developing arrays of position-sensitive microcalorimeters for future x-ray astronomy applications. These position-sensitive devices commonly referred to as hydras consist of multiple x-ray absorbers, each with a different thermal coupling to a single-transition-edge sensor microcalorimeter. Their development is motivated by a desire to achieve very large pixel arrays with some modest compromise in performance. We report on the design, optimization, and first results from devices with small pitch pixels (〈75 m) being developed for a high-angular and energy resolution imaging spectrometer for Lynx. The Lynx x-ray space telescope is a flagship mission concept under study for the National Academy of Science 2020 decadal survey. Broadband full-width-half-maximum (FWHM) resolution measurements on a 9-pixel hydra have demonstrated E(FWHM) = 2.23 0.14 eV at Al-K, E(FWHM) = 2.44 0.29 eV at Mn-K, and E(FWHM) = 3.39 0.23 eV at Cu-K. Position discrimination is demonstrated to energies below 〈1 keV and the device performance is well-described by a finite-element model. Results from a prototype 20-pixel hydra with absorbers on a 50-m pitch have shown E(FWHM) = 3.38 0.20 eV at Cr-K1. We are now optimizing designs specifically for Lynx and extending the number of absorbers up to 25/hydra. Numerical simulation suggests optimized designs could achieve 3 eV while being compatible with the bandwidth requirements of the state-of-the art multiplexed readout schemes, thus making a 100,000 pixel microcalorimeter instrument a realistic goal.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN75245 , Journal of Astronomical Telescopes, Instruments and Systems; 5; 2; 021008
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  • 9
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    The Nearby Evolved Stars Survey I. JCMT/SCUBA-2 Submillimeter Detection of the Detached Shell of U Antliae (2019)
    In:  CASI
    Details
    Publication Date: 2019-12-27
    Description: We present the highest resolution single-dish submillimetre observations of the detached shell source U Antliae to date. The observations were obtained at 450 and 850m with SCUBA-2 instrument on the James Clerk Maxwell Telescope as part of the Nearby Evolved Stars Survey. The emission at 850m peaks at 40 arcsec with hints of a second peak seen at 20 arcsec. The emission can be traced out to a radius of 56 arcsec at a 3 level. The outer peak observed at 850m aligns well with the peak observed at Herschel/PACS wavelengths. With the help of spectral energy distribution fitting and radiative transfer calculations of multiple-shell models for the circumstellar envelope, we explore the various shell structures and the variation of grain sizes along the in the circumstellar envelope. We determine a total shell dust mass of (2.0 0.3) 105 M and established that the thermal pulse that gave rise to the detached shell occurred 3500 500 yr ago.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN74201 , Monthly Notice of the Royal Astronomical Society; 489; 3; 3218–3231
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  • 10
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    The Solar Neutron TRACking (SONTRAC) Instrument for the Detection of Fast Neutrons (2019)
    In:  CASI
    Details
    Publication Date: 2019-12-27
    Description: The detection of fast neutrons has important applications in several fields including solar, Geospace and planetary physics. Neutrons are challenging to detect and measurements of them typically suffer from high background rates. High-energy neutrons (〉50 MeV) pose even more challenges, because the traditional double-scatter technique based on a time-of-flight (ToF) measurement is limited by short flight paths and small detector sizes characteristic of small satellite platforms. It is now possible to perform high-energy neutron measurements inside a large monolithic detector by imaging the recoil proton tracks, thus eliminating the need for a measure of the time-of-flight. The concept is based on a spectrometer assembled from numerous thin hydrogenous scintillating fibers that allow ionization track imaging. Fine grained readout is now possible with arrays of1-mm pitch silicon photomultipliers (SiPMs). The Solar Neutron TRACking (SONTRAC) instrument, equipped with scintillating fibers readout with SiPMs sensors, provides high-resolution, fine grained, imaging of fast (between 20-200 MeV) neutron scatters in a compact, low-power design ideal for small satellite(and aircraft) platforms. We discuss below applications of this technology and performance characteristics of the prototype SONTRAC instrument.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN72138 , IEEE Nuclear Science Symposium & Medical Imaging Conference; Oct 26, 2019 - Nov 02, 2019; Manchester, England; United Kingdom
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