The Compact Symmetric Objects (CSOs) are small (<1 kiloparsec) and powerful extragalactic radio sources showing emission on both sides of an active galactic nucleus and no signs of strong relativistic beaming. They may be young radio sources, progenitors of large FRII radio galaxies. We aim to study the statistical properties of CSOs by constructing and investigating a new large sample of CSO candidates on the basis of dual-frequency, parsec-scale morphology. For the candidate selection we utilized VLBI data for 4170 extragalactic objects obtained simultaneously at 2.3 and 8.6 GHz (S and X band) within the VLBA Calibrator Survey 1-6 and the Research and Development - VLBA projects. Properties of their broad-band radio spectra were characterized by using RATAN-600 observations. Numerical modeling was applied in an attempt to explain the observed effects. A sample of 64 candidate CSOs is identified. The median two-point S-X band spectral index of parsec-scale hotspots is found to be -0.52; with the median brightness temperature ~10^9 K at X band. Statistical analysis reveals a systematic difference between positions of brightest CSO components (associated with hotspots) measured in the S and X bands. The distance between these components is found to be on average 0.32+/-0.06 mas greater at 8.6 GHz than at 2.3 GHz. This difference in distances cannot be explained by different resolutions at the S and X bands. It is a manifestation of spectral index gradients across CSO components, which may potentially provide important physical information about them. Despite our detailed numerical modeling of a CSO hotspot, the model was not able to reproduce the magnitude of the observed positional difference. A more detailed modeling may shed light on the origin of the effect.
Spectroscopic redshifts of selected flat-spectrum radio sources I
Institute of Astrophysics, Foundation for Research and Technology – Hellas（希腊研究与技术基金会天体物理研究所）；University of Crete（克里特大学）；National Institute for Astrophysics (INAF), Astronomical Observatory of Padova（意大利国家天体物理研究所帕多瓦天文台）
On the Possibility of an Extragalactic Positron Annihilation Signal
Julius-Maximilians-Universität Würzburg（维尔茨堡大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学博雅中心）；Department of Physics, Kyoto University（京都大学物理系）；RIKEN Nishina Center（理化学研究所西村中心）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo（东京大学宇宙线研究所 Kavli宇宙物理数学研究所）
