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  • ASTROPHYSICS  (5)
  • MECHANICAL ENGINEERING  (1)
  • SPACE RADIATION  (1)
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  • 1
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    Basic physics and cosmology from pulsar timing data (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Radio pulsars provide unparalleled opportunities for making measurements of astrophysically interesting phenomena. The author concentrates on two particular applications of high precision timing observations of pulsars: tests of relativistic gravitation theory using the binary pulsar 1913+16, and tests of cosmological models using timing data from millisecond pulsars. New upper limits are presented for the energy density of a cosmic background of low frequency gravitational radiation.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 385-393
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Radio pulsar timing observations for GRO (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Gamma rays probably provide the best diagnostic tool for probing the enigmatic physics of pulsar magnetospheres. At present, however, only two pulsars - the young, nearby ones in the Crab and Vela X supernova remnants - are reliably detected at gamma-ray energies. With adequate radio observations to provide independent timing information, Gamma Ray Observatory should be able to detect a number of additional pulsars, and the results will be of great benefit in testing magnetospheric theories and models. Timing observations for this purpose were started at a number of radio observatories around the world. The general procedures being used are described. A status report on the work is given.
    Keywords: SPACE RADIATION
    Type: NASA, Goddard Space Flight Center, The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium; p 81-87
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    High-precision timing of millisecond pulsars. II - Astrometry, orbital evolution, and eclipses of PSR 1957 + 20 (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Pulse time-of-arrival measurements have been acquired for PSR 1957 + 20 on 61 days over a 2.7 yr interval, including the times of 44 eclipse disappearance or reappearance events. The timing data provide a reliable measurement of the pulsar's proper motion, 29 +/- 3 mas/yr, at position angle 216 +/- 6 deg; this direction is in excellent agreement with that suggested by the cometlike shape of a surrounding optical emission nebula. The rate of change of the orbital period has been measured: a surprisingly large (-3.9 +/- 0.9) x 10 exp -11, implying that significant orbital evolution must take place on a time scale of 30 Myr. Finally, the present observations extend the eclipse measurements to higher frequencies and provide better statistics for these highly variable phenomena. The eclipse data are used to compute a column-density profile of free electrons in the outer parts of the eclipsing region, and thereby provide an important glimpse into the material being ablated from the companion star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 380; 557-563
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    NASA TECHNICAL REPORTS
  • 4
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    The Parallax of Pulsar 0950+08 and the Local Free Electron Density (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: A parallax of 7.9 + or - 0.8 mas for PSR 0950+08, corresponding to a distance of 130 + or - 15 pc is reported. The measured pulse dispersion of this pulsar implies an average free electron density of 0.023 + or 0.002/cu cm along the line of sight. This parallax measurement is subject to systematic errors and questions of interpretation which are not yet fully explored.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 281-283
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  • 5
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    Dynamic data acquisition, reduction, and analysis for the identification of high-speed compressor component post-stability characteristics (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A compressor test was conducted in which transient data were obtained for the purpose of identifying the high-speed post-stability characteristics. The transient, surge-cycle nature of high-speed post-stability operation precludes the possibility of obtaining the characteristics in a steady-state manner, as is possible during low-speed poststability operation, which is characterized by quasi-steady rotating-stall behavior. Specialized compressor instrumentation was developed and was used to obtain the necessary surge-cycle performance data, which were then digitized, filtered, and analyzed. The high-speed post-stability characteristics were obtained through the use of a maximum likelihood-parameter estimation technique. The estimated characteristics were found to be insensitive to the presence of measurement noise and unmodelled system dynamics, but the compressor time-response constants, which were also estimated, were more sensitive to these same disturbances.
    Keywords: MECHANICAL ENGINEERING
    Type: AIAA PAPER 87-2089
    Format: text
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  • 6
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    Two newly discovered millisecond pulsars (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: Two millisecond pulsars have been discovered in the course of systematic surveys being made with the Arecibo radio telescope. PSR J2019 + 2425 has a 3.935 ms period and moves in a nearly circular, 76.5 day orbit around a about 0.3 solar mass companion. PSR J2322 + 2057, with a period of 4.808 ms, is an isolated object. The two pulsars have unusually small period derivatives, corresponding to spin-down time scales of 7.5 +/- 0.5 and 11 +/- 5 Gyr, respectively. Both objects show pulse time-of-arrival residuals no larger than a few microseconds over many months, lending further support to the observation that 'recycled' pulsars have extremely stable rotational behavior. The timing results also confirm that physics related to the rotational dynamics of these strongly self-gravitating stars - in particular, the value of the gravitational coupling constant G - remains essentially constant over time scales comparable to the Hubble time. Dispersion measures of the two pulsars indicate distances of 0.8-0.9 kpc.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 402; 2; p. L49-L52.
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  • 7
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    Pulsar distances and the galactic distribution of free electrons (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The present quantitative model for Galactic free electron distribution abandons the assumption of axisymmetry and explicitly incorporates spiral arms; their shapes and locations are derived from existing radio and optical observations of H II regions. The Gum Nebula's dispersion-measure contributions are also explicitly modeled. Adjustable quantities are calibrated by reference to three different types of data. The new model is estimated to furnish distance estimates to known pulsars that are accurate to about 25 percent.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal - Part 1 (ISSN 0004-637X); 411; 2; p. 674-684.
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