We present the results of simultaneous multifrequency imaging observations at 22, 43, 86, and 129 GHz of OJ 287. We used the Korean Very Long Baseline Interferometry Network as part of the Interferometric Monitoring of Gamma-ray Bright active galactic nuclei (iMOGABA). The iMOGABA observations were performed during 31 epochs from 2013 January 16 to 2016 December 28. We also used 15 GHz OVRO and 225 GHz SMA flux density data. We analyzed four flux enhancements in the light curves. The estimated timescales of three flux enhancements were similar with timescales of ∼50 days at two frequencies. A fourth flux enhancement had a variability timescale approximately twice as long. We found that 225 GHz enhancements led the 15 GHz enhancements by a range of 7–30 days in the time delay analysis. We found the fractional variability did not change with frequency between 43 and 86 GHz. We could reliably measure the turnover frequency, , of the core of the source in three epochs. This was measured to be in a range from 27 to 50 GHz and a flux density at the turnover frequency, , ranging from 3 to 6 Jy. The derived SSA magnetic fields, , are in a range from 0.157 ± 0.104 to 0.255 ± 0.146 mG. We estimated the equipartition magnetic field strengths to be in a range from 0.95 ± 0.15 to 1.93 ± 0.30 mG. The equipartition magnetic field strengths are up to a factor of 10 higher than the values of . We conclude that the downstream jet may be more particle energy dominated.

We report on the spectral variability of the blazar 3C 279 in the optical to X-ray band between MJD 55100 and 58400 during which long-term radio variability was observed. We construct light curves and band spectra in each of the optical (2 × 1014–1.5 × 1015 Hz) and X-ray (0.3–10 keV) bands, measure the spectral parameters (flux F and spectral index α), and investigate the correlation between F and α within and across the bands. We find that the correlation of the optical properties dramatically change after ∼MJD 55500 and the light curves show more frequent activity after ∼MJD 57700. We therefore divide the time interval into three “states” based on the correlation properties and source activity in the light curves, and analyze each of the three states separately. We find various correlations between the spectral parameters in the states and an intriguing 65 day delay of the optical emission with respect to the X-ray one in state 2 (MJD 55500–57700). We attempt to explain these findings using a one-zone synchro-Compton emission scenario.

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Symmetric varieties are normal equivarient open embeddings of symmetric homogeneous spaces, and they are interesting examples of spherical varieties. We prove that all smooth Fano symmetric varieties with Picard number one admit Kähler–Einstein metrics by using a combinatorial criterion for K-stability of Fano spherical varieties obtained by Delcroix. For this purpose, we present their algebraic moment polytopes and compute the barycenter of each moment polytope with respect to the Duistermaat–Heckman measure.

Let p : X → Y be a surjective holomorphic mapping between Kähler manifolds. Let D be a bounded smooth domain in X such that every generic fiber D y := D ∩ p −1 (y) for y ∈ Y is a strongly pseudoconvex domain in X y := p −1 (y), which admits the complete Kähler-Einstein metric. This family of Kähler-Einstein metrics induces a smooth (1, 1)-form ρ on D. In this paper, we prove that ρ is positive-definite on D if D is strongly pseudoconvex. We also discuss the extensioin of ρ as a positive current across singular fibers.