Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976apj...207..937v&link_type=abstract
Astrophysical Journal, vol. 207, Aug. 1, 1976, pt. 1, p. 937-948.
Astronomy and Astrophysics
Astronomy
14
Crab Nebula, Interferometry, Pulsars, Size (Dimensions), Brightness, Diameters, Fine Structure, Pulse Duration, Radio Sources (Astronomy), Visibility
Scientific paper
Observations of pulsars, especially the Crab Nebula pulsar, made in very long baseline interferometry (VLBI) experiments are discussed. Based on a crude 144 MHz visibility curve which is consistent with a Gaussian brightness distribution, the measured visibilities at 196, 111, and 74 MHz were interpreted to yield apparent angular diameters (at half-power) of about 0.03 sec, 0.07 sec, and 0.18 sec, respectively. These sizes scale approximately as wavelength-squared, and the 74 MHz size agrees with recent observations using interplanetary scintillation techniques. The total flux densities lie on the extrapolation from higher frequencies of the pulsing flux densities. Variations in the total flux density up to 25 per cent were observed. A lack of fine structure other than the pulsar in the nebula is indicated by the simple visibility curves. The pulse shapes are similar to single-dish measurements at 196 MHz but reveal a steady, nonpulsing component at 111 MHz. The ratio of pulsing to total power was approximately equal to one-half but varied with time. It was found that four strong, low-dispersion pulsars were only slightly resolved.
Broderick John J.
Clark Thomas A.
Erickson William C.
Resch George M.
Vandenberg Nancy R.
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