2003/11/17 by A. Caccianiga, M. J. M. Marchã, M. J. M. Marcha
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Blazar #Galaxy #Gamma ray #Neutrino Physics Research #Physics #ROSAT #Radio Astronomy Observations and Technology #Radio galaxy #Sky #Spectral index #Spectral line #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2004.07415.x
published as Mon.Not.Roy.Astron.Soc. 348 (2004) 937 · 20 pages, accepted for publication in MNRAS
arxiv created 2003/11/17 · openalex publication_date 2004/02/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We discuss the properties of the sources in the CLASS blazar survey, which aims at the selection of low radio power (P5 GHz < 1025 W Hz−1) blazars. We use Very Large Array (VLA) data from available catalogues and from our own observations to constrain the radio core-dominance of the sample which, together with the flat radio spectral index, is a signature of the blazar activity. X-ray data from the ROSAT All Sky Survey were also collected in order to constrain the radio-to-X-ray luminosity ratio (αRX) of the sources. The data analysis shows that more than 30 per cent of sources at low radio power (P5 GHz < 1025 W Hz−1) have an αRX steeper than that expected in the framework of the ‘blazar sequence’ recently put forward to unify the high- and low-power blazars. The possibility that this result is influenced by contaminating sources in the current sample is discussed. The conclusion is that, even if a number of non-blazars (typically CSO/GPS sources) are expected in the survey, it is unlikely that this constitutes the sole reason for the observed deviation. In particular, we show two examples for which the blazar nature is confirmed from VLBI data and for which the steep αRX (suggesting a synchrotron peak frequency below 1015.5 Hz) and the low radio power (0.6–2 × 1024 W Hz−1) put these sources outside the ‘blazar sequence’. The results presented here show the importance of a correct and unbiased sampling of the low-power regime of the blazar population.