318-MHz variability of complete samples of extragalactic radio sources

Journal Article · Mon Jan 01 04:00:00 EST 1979 · Astron. J.; (United States)

DOI:https://doi.org/10.1086/112381· OSTI ID:6799162

Condon, J J; Ledden, J E; O'Dell, S L; Dennison, B

Flux-density measurements at 318 MHz were made during two epochs, separated by approximately 7 yr, of extragalactic sources in samples complete to 3 Jy at 1400 MHz and 1 Jy at 5000 MHz. Steep-spectrum (..cap alpha..> or =+0.5) sources do not appear to vary, but at least 1/4 of the flat-spectrum (..cap alpha..<+0.5) sources observed were found to be low-frequency variables on time scales of decades. Several 318 and 606 MHz flux-density measurements made from 1969 to 1971 confirm Hunstead's discovery (Astrophys. Lett. 12, 193 (1972)) of 408-MHz variability in 3C 454.3 on a time scale of only a few years. Various explanations for low-frequency variability: noncosmological redshifts, intergalactic scintillations, variable absorbing shells, coherent emission mechanisms, special geometries, and relativistic expansion of incoherent electron--synchrotron components: were considered in the light of the observations. We conclude that relativistic expansion of sources emitting incoherent electron--synchrotron radiation is in best agreement with the data, although the rapid variations observed in 3C 454.3 during 1969--1971 are still difficult to understand quantitatively.

• Research Organization: National Radio Astronomy Observatory, Edgemont Road, Charlottesville, Virginia 22901
• OSTI ID: 6799162
• Journal Information: Astron. J.; (United States), Journal Name: Astron. J.; (United States) Vol. 84:1; ISSN ANJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics &amp; Cosmology-- Quasi-Stellar
Radio
&amp; X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANTENNAS
BREMSSTRAHLUNG
BRIGHTNESS
COSMIC RADIO SOURCES
ELECTRICAL EQUIPMENT
ELECTROMAGNETIC RADIATION
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUX DENSITY
GALAXIES
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
RADIO EQUIPMENT
RADIO GALAXIES
RADIO TELESCOPES
RED SHIFT
SYNCHROTRON RADIATION
TELESCOPES
VARIATIONS