M. H. Cohen

The small-scale structure of radio galaxies and quasi-stellar sources at 3.8 centimeters.

Observation of fringes from 31 compact radio sources, including eight known or suspected galaxies and 20 known or suspected QSSs, by using the Goldstack interferometer at lambda = 3.8 cm (d/lambda = 10 to the 8th power). Fringe visibility curves were obtained for nine sources showing structure on a scale of .001 sec of arc, and simple models are fitted to the data. Results for 3C 273 and 3C 279 are compared with data taken by Knight et al. (1971) at an earlier epoch. The apparent changes in brightness distribution of 3C 273 and 3C 279 are difficult to explain.

Further monitoring of the structure of superluminal radio sources

We have studied the sources 3C 120, 3C 273, 3C 279, and 3C 345 at six epochs between 1975.40 and 1977.13 using long baseline interferometry at 10.65 GHz, and at 1976.52 and 1977.41 at 5.01 GHz. The sources 3C 120 (usually) and 3C 345 (always) appear as double radio sources whose components are separating along constant potition angles. Assuming their redshifts are cosmological, the apparent transverse velocities of separation are v/c=6.7 +- 0.8 beginning in 1966.3 +- 0.3 yr for 3C 345 and, for 3C 120, v/c=4.1 +- 0.4 beginning in 1972.4 +- 0.5 yr and continuing into 1974, then v/c=8.5 +- 0.9 beginning in 1974.4 +- 0.2 yr and continuing until mid-1976. No models of 3C 273 are derived, but evidence for superluminal expansion is presented, showing v/c=5.2 +- 0.5 beginning in 1967.6 +- 0.4 yr. Visibility functions of 3C 279 have changed very little over the period 1976.39 +- 1977.41.

Very high-resolution observations of the radio sources NRAO 150, OJ 287, 3C 273, M87, 1633+38, BL Lacertae, and 3C 454. 3

Very long baseline interferometer observations made at a wavelength of 2 and 2.8 cm with baselines ranging from 54 to 291 million wavelengths show a number of radio sources with only slightly resolved components, even on the longest baselines; the quasars 1633 + 38 and 3C 454.3, the objects OJ 287 and BL Lac, and the nucleus of M87 (Virgo A, 3C 274) all contain components < or approximately 0.4 milli-arcsec. The smallest component observed is in the core of 3C 454.3, which contains about 50% of the total flux density and is < or approximately 0.2 milli-arcsec in diameter. The compact component in the nucleus of M87 is < or approximately 1.5 light-months across, and contains about one-third of the total flux density of the nucleus at 2.8 cm. NRAO 150 and BL Lac are double: the components of NRAO 150 are separated by 0.6 milli-arcsec, while BL Lac has an elongated structure consisting of a large (1.4 milli-arcsec) component separated by 1.25 milli-arcsec from a smaller (0.5 milli-arcsec) variable one. The present data on 3C 273 are consistent with triple models similar to those discussed previously, but with a somewhat greater apparent separation of components.

A compact radio source in the nucleus of M82

Abstract : The compact radio source in M 87 has been observed with a long baseline interferometer composed of the 210-foot telescope at Goldstone, California, U.S.A., and the 85-foot telescope at Tidbinbilla, near Canberra, A.C.T., Australia. The observations suggest that the radio source is remarkably concentrated to the galactic nucleus and has a linear diameter of about 2.5 light months.

The compact radio sources in 4C 39.25 and 3C 345

Long-baseline interferometry of the quasars 4C 39.25 and 3C 345 at 10.65 and 14.77 GHz shows that the centimeter radio source in each object is double, with component separations of 0.0020 arcsec (4C 39.25) and 0.0013 arcsec (3C 345 at 1974.5). For each source, the separation is the same at both frequencies, as well as similar to the structure observed at 7.85 GHz (and 5.0 GHz for 4C 39.25). The spectra of the individual components are derived and shown to vary with time approximately as expected for expanding self-absorbed synchrotron sources. The magnetic fields in the components are estimated to be as high as 0.1 gauss, but the structure of the sources appears to be unrelated to the magnetic-field orientation derived from low-resolution polarization measurements. The component separation in 4C 39.25 has not changed for several years, whereas 3C 345 shows rapid expansion.

Rapid increase in the size of 3C 345

The brightness distribution of the quasar 3C 345 at lambda=2.8 cm is accurately modeled with two Gaussian elliptical components. Observations at four epochs between 1974.15 and 1975.68 show that the separation of the components increased from 1.23 to about 1.61 milli-arcsec, at a rate 0.2 milli-arcsec per year. The apparent transverse velocity is vapprox. =8c, if one assumes a cosmological interpretation of the redshift. (AIP)

Observations with a VLB array. II - The sources 4C 39.25, NRAO 150, VRO 42.22.01, 3C 345, and 3C 454.3

Three-antenna long-baseline interferometry at 10.7 GHz is reported for NRAO 150, 4C 39.25, 3C 345, VRO 42.22.01, and 3C 454.3 for several epochs between 1972 April and 1974 February. Simple models for the source brightness distributions fit the observations and indicate that most of the radio emission comes from one or two components. Component separations range up to approx.50 lt-yr, and component sizes are on the order of 10 lt-yr. Small variations in source structure have been observed.

Variations in the Radio Structure of BL Lacerate

We have observed the structure of the rapid variable radio source BL Lac (VRO 42.22.01) using long baseline interferometer systems with baselines up to 266 million wavelengths. Despite large variations in the total flux and in the overall size of this source, it has maintained an elongated brightness distribution, and the direction of elongation has not changed during the 1.3 years of observation. No simple model of stationary variable components or of separating, evolving components appears to fit all the data For this source. In particular, it apparently cannot be explained in terms of a stationary brightness distribution with a single variable component of very small angular size. The peak brightness temperature of VRO 42.22.01 is in excess of 5x 10/sup 12/. K at 11 cm wavelength, a value close to the limit set by inverse Compton scattering.

Observations of further outbursts in the radio galaxy 3C 120.

interferometer observations made during two years with the Goldstack interferometer show considerable increases and decreases in the apparent angular size of the radio galaxy 3C 120. The data suggest that the outbursts occur in regions separated by several light years but are also consistent with the individual components expanding or moving with an apparent velocity close to the speed of light.