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  • Astrophysics  (4)
  • Cybernetics, Artificial Intelligence and Robotics; Earth Resources and Remote Sensing  (1)
  • Computer Systems; Earth Resources and Remote Sensing
  • Space Sciences (General)
  • 2015-2019  (5)
  • 2010-2014
  • 2005-2009
  • 2018  (5)
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  • 2015-2019  (5)
  • 2010-2014
  • 2005-2009
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  • 1
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    Detection of Reflection Features in the Neutron Star Low-mass X-Ray Binary Serpens X-1 with NICER (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present Neutron Star Interior Composition Explorer (NICER) observations of the neutron star (NS) low-mass X-ray binary Serpens X-1 during the early mission phase in 2017. With the high spectral sensitivity and low-energy X-ray passband of NICER, we are able to detect the Fe L line complex in addition to the signature broad, asymmetric Fe K line. We confirm the presence of these lines by comparing the NICER data to archival observations with XMM-Newton/Reflection Grating Spectrometer (RGS) and NuSTAR. Both features originate close to the innermost stable circular orbit (ISCO). When modeling the lines with the relativistic line model RELLINE, we find that the Fe L blend requires an inner disk radius of 1.4(sup 0.2, sub -0.1)R(sub ISCO) and Fe K is at 1.03(sup 0.13, sub -0.03)R(sub ISCO) (errors quoted at 90%). This corresponds to a position of 17(sup 2.5, sub -1.2)km and 12(sup 1.6, sub -0.4)km for a canonical NS mass (M(sub NS)=1.4 solar mass) and dimensionless spin value of a = 0. Additionally, we employ a new version of the RELXILL model tailored for NS(sub s) and determine that these features arise from a dense disk and supersolar Fe abundance.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN57931 , The Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 858; L5; No. 1
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  • 2
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    A NICER Spectrum of MAXI J1535-571: Near-Maximal Black Hole Spin and Potential Disk Warping (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We report on a Neutron star Interior Composition Explorer (NICER) observation of the Galactic X-ray binary and stellar-mass black hole candidate, MAXI J1535571. The source was likely observed in an "intermediate" or "very high" state, with important contributions from both an accretion disk and hard X-ray corona. The 2.3-10 keV spectrum shows clear hallmarks of relativistic disk reflection. Fits with a suitable model strongly indicate a nearmaximal spin parameter of a = cJ/GM(exp 2) = 0.994(2) and a disk that extends close to the innermost stable circular orbit, r/r(sub ISCO) = 1.08(8) (1 statistical errors). In addition to the relativistic spectrum from the innermost disk, a relatively narrow Fe K emission line is also required. The resolution of NICER reveals that the narrow line may be asymmetric, indicating a specific range of emission radii. Fits with a relativistic line model suggest an inner radius of r = 144 +140/-60 GM/c(exp 2) for the putative second reflection geometry; full reflection models suggest that radii a few times larger are possible. The origin of the narrow line is uncertain, but a warp likely provides the most physically plausible explanation. We discuss our results in terms of the potential for NICER to reveal new features of the inner and intermediate accretion disk around black holes.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN60607 , Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 860; 2; L28
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  • 3
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    NICER Observes the Effects of an X-Ray Burst on the Accretion Environment in Aql X-1 (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Accretion disks around neutron stars regularly undergo sudden strong irradiation by Type I X-raybursts powered by unstable thermonuclear burning on the stellar surface. We investigate the impacton the disk during one of the first X-ray burst observations with the Neutron Star Interior CompositionExplorer (NICER) on the International Space Station. The burst is seen from Aql X-1 during the hardspectral state. In addition to thermal emission from the neutron star, the burst spectrum exhibits anexcess of soft X-ray photons below 1 keV, where NICER's sensitivity peaks. We interpret the excessas a combination of reprocessing by the strongly photoionized disk and enhancement of the pre-burstpersistent flux, possibly due to Poynting Robertson drag or coronal reprocessing. This is the firstsuch detection for a short sub-Eddington burst. As these bursts are observed frequently, NICER willbe able to study how X-ray bursts affect the disk and corona for a range of accreting neutron starsystems and disk states.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN66162 , Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 855; 1; L4
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  • 4
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    NICER Discovers mHz Oscillations in the "Clocked" Burster GS 1826-238 (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report the discovery with the Neutron Star Interior Composition Explorer (NICER) of mHz X-ray brightness oscillations from the "clocked burster" GS 1826238. NICER observed the source in the periods 2017 June 2029, July 1113, and September 915, for a total useful exposure of 34 ks. Two consecutive dwells obtained on 2017 September 9 revealed highly significant oscillations at a frequency of 8 mHz. The fractional, sinusoidal modulation amplitude increases from 0.7% at 1 keV to 2% at 6 keV. Similar oscillations were also detected at lower significance in three additional dwells. The oscillation frequency and amplitude are consistent with those of mHz QPOs reported in other accreting neutron star systems. A thermonuclear X-ray burst was also observed on 2017 June 22. The burst properties and X-ray colors are both consistent with GS 1826 being in a soft spectral state during these observations, findings that are confirmed by ongoing monitoring with MAXI and SWIFT-BAT. Assuming that the mHz oscillations are associated with blackbody emission from the neutron star surface, modeling of the phase-resolved spectra shows that the oscillation is consistent with being produced by modulation of the temperature component of this emission. In this interpretation, the blackbody normalization, proportional to the emitting surface area, is consistent with being constant through the oscillation cycle. We place the observations in the context of the current theory of marginally stable burning and briefly discuss the potential for constraining neutron star properties using mHz oscillations.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN66108 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 865; 1; 63
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  • 5
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    Earth Science Deep Learning: Applications and Lessons Learned (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Deep learning has revolutionized computer vision and natural language processing with various algorithms scaled using high-performance computing. At the NASA Marshall Space Flight Center (MSFC), the Data Science and Informatics Group (DSIG) has been using deep learning for a variety of Earth science applications. This paper provides examples of the applications and also addresses some of the challenges that were encountered.
    Keywords: Cybernetics, Artificial Intelligence and Robotics; Earth Resources and Remote Sensing
    Type: MSFC-E-DAA-TN51352 , IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2018); Jul 22, 2018 - Jul 27, 2018; Valencia; Spain
    Format: application/pdf
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