A&A 435, 839-856 (2005)
Long term variability of gigahertz-peaked spectrum sources and candidatesI. Torniainen1, M. Tornikoski1, H. Teräsranta1, M. F. Aller2 and H. D. Aller2 1
Metsähovi Radio Observatory, Helsinki University of Technology,
Kylmäläntie 114, 02540 Kylmälä, Finland
Department of Astronomy, University of Michigan, Ann Arbor, MI, 48109 USA
(Received 24 August 2004 / Accepted 14 February 2005)
We have combined new data from our observing campaigns and data from
the literature to construct the radio continuum spectra for a sample
of mostly quasar-type high peaking gigahertz-peaked spectrum (GPS)
source candidates. We have also studied the spectra and variability
of so called "bona fide" GPS sources and other inverted-spectrum
sources from the literature. For many of our sample sources we now
have data spanning over two decades, enabling us to study their long
Based on our earlier results we expected to find several new high
peaking GPS sources. Instead we found out that even most of the "bona fide" GPS sources cease to adhere to the generic GPS source properties
when using these well-sampled long term data sets.
In our sample of 35 inverted-spectrum sources from the literature only five seem to
be consistent with the GPS properties, and even out of these sources
two are too sparsely sampled to firmly make conclusions about their variability.
Thirteen of the "bona fide" GPS sources exhibit pronounced
activity, which diverges from the low variability expected from these
sources. None of our new candidates turned out to have both a convex spectrum
and little to no variability, but there is one variable source with a
consistently convex spectrum. All the rest have flat spectra, but the upper
envelope of the spectrum is clearly convex for four extremely variable sources.
Similar continuum spectra with a flat lower envelope and a
convex upper envelope are observed for eight previously identified inverted-spectrum sources.
According to this study the genuine quasar-type GPS sources are rare
but there is a large number of highly variable sources that can have
a convex spectrum peaking at high radio frequencies (up to ca. 100 GHz)
during flares. Many of the GPS sources from the literature have too
easily been classified as GPS sources based on too sparse data,
and studying the long term variability is essential for identifying
the sources with consistently convex continuum spectra.
galaxies: quasars: general
© ESO 2005