Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295...47q&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 1, p. 47-53
Astronomy and Astrophysics
Astrophysics
15
Astronomical Models, Flux Density, Periodic Variations, Quasars, Refractivity, Scintillation, Extragalactic Radio Sources, Galactic Structure, Interstellar Matter, Light Scattering, Power Spectra, Spectrum Analysis
Scientific paper
The structure functions D(tau) of the flux density variations at 2.7 GHz and 8.1 GHz in the compact radio source 1741-038 (z = 1.054) are compared with those at 1.5, 4.9, 15 and 22 GHz given by Hjellming & Narayan (1986) for a similar observing period. It is shown that for time lags 5 is less than or approximately tau is less than or approximately 30 days the structure functions at 2.7 GHz and 1.5 GHz are very similar and can be approximately represented by a power lae D(tau) varies as taup with index p approximately 1.7 - 1.8. The structure functions at 8.1, 15 and 22 GHz differ from those at the lower frequencies. A two-component model involving the extended Galactic interstellar medium and a thin screen with enhanced scattering strength is proposed. Using the refractive interstellar scintillation theory, the theoretical structure functions for the six observing frequencies are calculated. It is shown that the observed structure functions at 1.5 and 2.7 GHz can be well fitted by the model. The theoretical structure functions for the three higher frequencies (8.1, 15 and 22 GHz) are found to be much smaller than the observed structure functions. Thus the high frequency variations can not be fitted within the presently discussed RISS models and are probably intrinsic to the source.
Britzen Silke
Krichbaum Thomas P.
Qian Shan-Jie
Waltman Elizabeth
Wegner Ralf
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