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A fast-scan extragalactic source survey at 4.755 GHz.
I - Source list and radio spectra
OWEN, F. N.; LEDDEN, J. E.; CONDON, J. J.
Astronomical Journal, vol. 88, Jan. 1983, p. 1-15. l.
A survey of extragalactic radio sources made using driven declination scans
is reported covering an area of about 0.07 sr to a limiting flux density of
35 mJy. The fast-scan survey was carried out at a galactic latitude greater
than 17 deg with the NRAO 91-m telescope operating at 4.755 GHz, and the 480
sources detected were reobserved at 1.4 GHz with the National Astronomy and
Ionosphere Center 305-m telescope at Arecibo. The survey list, source counts
and spectral index distribution are presented, and it is noted that the
results confirm previous reports of a monotonic decline in the fraction of
flat-spectrum sources with decreasing flux density.
Simultaneous radio spectra of sources with strong millimeter components
Owen, F. N.; Spanger, S. R.; Cotton, W. D.
Astronomical Journal, vol. 85, Apr. 1980, p. 351-362.
Simultaneous radio spectra (within a 36-day period) are presented for
136 sources with flat or inverted spectra at centimeter wavelengths.
Flux densities were measured at up to 11 frequencies ranging from 318 MHz
to 90 GHz. At low frequencies (less than 1 GHz) a comparison of our data
with previous measurements yielded several new low-frequency variables.
The observations below 1 GHz also showed that many flat-spectrum sources
have an upturn in their spectra below 1 GHz, probably owing to an optically
thin 'halo.' Very few, if any, sources seem to have a real low-frequency cutoff.
At 5 GHz, sources with high-frequency turnovers below 30 GHz showed much less
variability over one year than those which were stronger than 1 Jy at 90 GHz. H
However, sources with S(90) greater than 1 Jy had variations only a little
larger at 90 GHz than at 5 GHz. This latter result seems inconsistent with
either simple inhomogeneous or relativistic Maxwellian models.
Models with relativistic jets close to the line of sight can probably account
for most of our results.
Observations of radio sources with flat spectra
Owen, F. N.; Porcas, R. W.; Mufson, S. L.; Moffett, T. J.
Astronomical Journal, vol. 83, July 1978, p. 685-696.
CENTIMETER WAVES, RADIANT FLUX DENSITY, RADIO SOURCES (ASTRONOMY),
RADIO SPECTRA, UBV SPECTRA, ASTRONOMICAL PHOTOMETRY, OPTICAL EMISSION
SPECTROSCOPY, OPTICAL THICKNESS
Results are reported for simultaneous or nearly simultaneous optical and
radio observations of 237 sources with flat or inverted radio spectra at
centimeter wavelengths. The observations include radiometry of all 237
sources at 90 GHz, radiometry of 104 sources at centimeter wavelengths
(central frequencies of 1.379, 4.585, 15.064, and 22.185 GHz), and optical
photometry of nine sources transformed to the Johnson UBV system. Optical
results are briefly discussed for the sources 1305+32 and 0851+20
(OJ 287), and the 90-GHz flux-density distribution is analyzed. The
radio spectra of the sources are examined, variability at 90 GHz is
investigated, and models for the radio emission are considered. It is
shown that: (1) the sources tend to have flat radio spectra over the
range from 1 to 100 GHz; (2) the weaker sources at 90 GHz have spectra
which tend to turn over at or near 5 GHz; (3) sources which turn over
at higher frequencies tend to be brighter optically; (4) BL Lac objects
tend to have flat spectra; (5) most of the strong sources are consistent
with a 90-GHz variability of less than 30% for one year; and (6) one or
more components with inhomogeneous structure are likely to exist in most
of the strong millimeter sources.