High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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BASIC PHYSICS AND COSMOLOGY FROM PULSAR TIMING DATA
BASIC PHYSICS AND COSMOLOGY FROM PULSAR TIMING DATA
Pages 385-393
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From page 385... ...
In this paper I concentrate on two particular applications of high precision tiIning 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.
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From page 386... ...
Observations made over intervals of about five minutes, or 1% of the ~ hour orbital penod, are used to accumulate samples of the periodic waveforms received Mom the pulsar. The pulse profiles are recorded digitally, along with accurate timing information from a reference atomic clock Subsequent analysis involves determining the equivalent topocentnc time of arrival, or TOA, for a pulse near the midpoint of each integration The complete set of TOAs is then analyzed in terms of a set of equations describing the pulsar's spill and orbital motions and the motions of the Earth.
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From page 387... ...
derived the first useful formulae for analyzing TOAs from binary pulsars. They treated the orbit as a slowly processing Keplerian ellipse; the ejects of relativistic time dilation and gravitational redshift were grafted onto the non-relativistic model, and additional phenomenological parameters were added to allow measurement of the rate of periastron precession and testing the constancy of other orbital parameters.
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From page 388... ...
According to conventional models, these parameters suggest unusually large ages and weak magnetic fields. Otherwise, however, the millisecond pulsars appear to be quite similar to their more slows rotating cousins.
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From page 390... ...
are a low frequency cutoff below f ~ r~t and a deep notch centered at f = 1 Arm, caused by the necessity to measure the celestial coordinates of the pulsar as part of the least-squares fitting process. ~ make it easy to compare the observed fluctuation spectra with hypothetical intrinsic spectra, I have multiplied the computed TO f)
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From page 391... ...
The observed power in the lowest spectral channel is well below this cuIve, and yields the conservative upper limit for the GWB quoted in the first line of Bible 1. In the center and bottom portions of Figure 4 are similar plots showing the observed spectra for the data from PSR 1937+21, together with instrumentally-modified power laws.
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From page 392... ...
, corresponding to the data sets illustrated in Figure ~ Dashed cuNes: hypothetical power-law spectra modified by the instrumental response functions T(f) , and arbitrarily normalized to the mean power level in the lowest two bins of S(f)
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From page 393... ...
The detailed implications of the numbers quoted in liable 1, particularly for model universes in which cosmic strings help to seed galaxy formation, are still somewhat controversial (Albrecht and lbrok 1989; Bennett and Bouchet 1989~. It is already clear, however, that the experimental limits are difficult to reconcile with the GWB energy density expected from cosmic string simulations, particularly when the strings retain sizes large enough to be useful in aiding galaxy formation.
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