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For refcode 1990A&AS...84..549O:
Retrieve 18 NED objects in this reference.
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1990A&AS...84..549O Multifrequency VLA observations of GHz-peaked-spectrum radio cores C.P. O'Dea, S.A. Baum, C. Stanghellini, G.B. Morris, A.R. Patnaik and Gopal-Krishna Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands Instituto di Radioastronomia del CNR, via Irnerio n. 46, I-40126 Bologna, Italy Dept. of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27514, U.S.A. Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, U.K. T.I.F.R. Radio Astronomy Centre, PO. Box 1234, Bangalore 5600l2, India T.I.F.R., GMRT Project, Poona University Campus, Ganeshkhind, Pune 411 007, India Received November 28, accepted December 7, 1989 Abstract. - We present simultaneous, multifrequency VLA observations of the cores of 18 suspected GPS sources. 3 of the 18 source, have flat spectra and are probably variable. The remaining 15 are confirmed as true GPS sources with spectral peaks between 0.8 and 6 GHz. Improved positions (~ 0.1" uncertainty) are reported for the cores of seven sources which are not VLA calibrators. Nine sources have steep high frequency spectra ({alpha} <~ -0.8) and ten (6 in common) have very inverted low frequency spectra ({alpha} >~ +0.8). The core of the compact double source 0108 + 388 has an optically-thick spectral index of {alpha} = +2.14+/-0.09 which is the most inverted (at centimeter wavelengths) of any compact extragalactic radio source currently known. We combined our data with recent high frequency measurements of four sources with the result that the high frequency spectra of these sources are found to either flatten or fail to steepen out to 90 GHz (230 GHz for 0552 + 398). The flattening of the spectrum indicates that there is very compact structure in two sources in addition to the components which peak near ~ 1 GHz. The fractional polarization at 22, 18, and 6 cm is remarkably low in the GPS sources. The majority of sources have polarizations less than 0.5% and only one source with an isolated core (i.e., not confused by extended emission) has a value greater than 1%. At 1.3 cm we obtain upper limits of a few percent for the polarization of isolated cores. Faraday rotation measures are obtained for four GPS sources. Two sources with polarizations above 1% have low RMs (less than 20 rad m^-2^) and two sources with polarizations below 1%, 0201 + 113 and 0552 + 398, may have very high rotation measures (|RM| ~ 650 rad m^-2^). For 0552 + 398, the RM in the rest frame of the source is ~ -7.4 x 10^3^ rad m^-2^. Key words: active galaxies - radio galaxies - polarization - quasars - radio sources.
Retrieve 18 NED objects in this reference.
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