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|Title:||A sample of weak blazars at milli-arcsecond resolution||Authors:||Mantovani, F.
MACK, KARL HEINZ
Zensus, J. A.
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||577||First Page:||A36||Abstract:||Aims: We started a follow-up investigation of the "Deep X-ray Radio Blazar Survey" objects with declination >-10 deg to better understand the blazar phenomenon. We undertook a survey with the European Very Long Baseline Interferometry Network at 5 GHz to make the first images of a complete sample of weak blazars, aiming at a follow-up comparison between high- and low-power samples of blazars. Methods: We observed 87 sources with the EVN at 5 GHz during the period October 2009 to May 2013. The observations were correlated at the Max-Planck-Institut für Radioastronomie and at the Joint Institute for VLBI in Europe. The correlator output was analysed using both the AIPS and DIFMAP software packages. <BR /> Results: All of the sources observed were detected. Point-like sources are found in 39 cases on a milli-arcsecond scale, and 48 show core-jet structure. The total flux density distribution at 5 GHz has a median value ⟨ S ⟩ = 44<SUP>+23</SUP><SUB>-10</SUB> mJy. A total flux density ≤150 mJy is observed in 68 out of 87 sources. Their brightness temperature T<SUB>b</SUB> ranges between 10<SUP>7</SUP> K and 10<SUP>12</SUP> K. According to the spectral indices previously obtained with multi-frequency observations, 58 sources show a flat spectral index, and 29 sources show a steep spectrum or a spectrum peaking at a frequency around 1-2 GHz. Adding to the DXRBS objects we observed those already observed with ATCA in the Southern sky, we found that 14 blazars and a Steep Spectrum Radio Quasars, are associated to γ-ray emitters. Conclusions: We found that 56 sources can be considered blazars. We also detected 2 flat spectrum narrow line radio galaxies. About 50% of the blazars associated to a γ-ray object are BL Lacs, confirming that they are more likely detected among blazars γ-emitters. We confirm the correlation found between the source core flux density and the γ-ray photon fluxes down to fainter flux densities. We also found that weak blazars are also weaker γ-ray emitters compared to bright blazars. Twenty-two sources are SSRQs or Compact Steep-spectrum Sources, and 7 are GigaHz Peaked Sources. The available X-ray ROSAT observations allow us to suggest that CSS and GPS quasars are not obscured by large column of cold gas surrounding the nuclei. We did not find any significant difference in X-ray luminosity between CSS and GPS quasars. <P />Appendix A is available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201425527/olm">http://www.aanda.org</A>||Acknowledgments:||The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement No 283393 (RadioNet3). E.R. acknowledges partial support by the Spanish MINECO project AYA2012-38941-C02-01 and the Generalitat Valenciana project PROMETEOII/2012/057. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team ( Lister et al. 2009 ). We are gratful to Alaksander Pushkarev for providing his data and to Lars Fuhrmann for all the suggestions while we were drafting the paper. This work made use of the Swinburne University of Technology software correlator, developed as part of the Australian Major National Research Facilities Programme and operated under licence. It has also used the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, and NASA’s Astrophysics Data System. We are very grateful to an anonymous referee for very helpful comments and suggestions and for a careful reading of the manuscript of this paper.||URI:||http://hdl.handle.net/20.500.12386/23451||URL:||https://www.aanda.org/articles/aa/abs/2015/05/aa25527-14/aa25527-14.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201425527||Bibcode ADS:||2015A&A...577A..36M||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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