We are carrying out the densest and longest multiyear, multiwavelength monitoring project of OJ 287 ever done. The project MOMO (Multiwavelength Observations and Modeling of OJ 287) covers ...wavelengths from the radio to the high‐energy regime. A few selected observations are simultaneous with those of the Event Horizon Telescope (EHT). MOMO aims at understanding disk‐jet physics and at testing predictions of the binary black hole scenario of OJ 287. Here, we present a discussion of extreme outburst and minima states in context, and then focus on the recent flux and spectral evolution between 2021 and May 2022, including an ongoing bright radio flare. Further, we show that there is no evidence for precursor flare activity in our optical–UV–X‐ray light curves that would be associated with any secondary supermassive black hole (SMBH) disk impact and that was predicted to start as thermal flare on December 23, 2021.
AgSnSe2, by formal electron count, should have Sn in a highly unusual 3+ valence state and was therefore suggested to be a valence-skipping compound with potential for negative-U centers and local ...electron pairing. It has been proposed that the latter may be the mechanism beyond seemingly conventional superconductivity in this compound. We report NMR measurements and first-principles calculations that agree with each other perfectly, and both indicate that valence skipping does not take place and the highly unusual Sn3+ state is realized instead, likely because of geometrical constraint prohibiting a breathing distortion that could screen the on-site Coulomb repulsion.
We report our intensive, high angular resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from 2011 ...February to 2012 October, together with contemporaneous high-energy (100 MeV <E < 100 GeV) γ-ray light curves obtained by the Fermi Large Area Telescope. During this period (specifically from 2012 February to 2012 March), an elevated level of the M 87 flux is reported at very high energy (VHE; E > 100 GeV) γ rays by VERITAS. We detected a remarkable (up to ∼70%) increase of the radio flux density from the unresolved jet base (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. Meanwhile, we confirmed with EVN at 5 GHz that the peculiar knot, HST-1, which is an alternative favored γ-ray production site located at ≳120 pc from the nucleus, remained quiescent in terms of its flux density and structure. These results in the radio bands strongly suggest that the VHE γ-ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. We further conducted VERA astrometry for the M 87 core at six epochs during the flaring period, and detected core shifts between 22 and 43 GHz, a mean value of which is similar to that measured in the previous astrometric measurements. We also discovered a clear frequency-dependent evolution of the radio core flare at 43, 22, and 5 GHz; the radio flux density increased more rapidly at higher frequencies with a larger amplitude, and the light curves clearly showed a time-lag between the peaks at 22 and 43 GHz, the value of which is constrained to be within ∼35-124 days. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity. By combining the obtained core shift and time-lag, we estimated an apparent speed of the newborn component propagating through the opaque region between the cores at 22 and 43 GHz. We derived a sub-luminal speed (less than ∼0.2c) for this component. This value is significantly slower than the super-luminal (∼1.1c) features that appeared from the core during the prominent VHE flaring event in 2008, suggesting that stronger VHE activity can be associated with the production of a higher Lorentz factor jet in M 87.
We explore energy densities of magnetic fields and relativistic electrons in M87 jet. Since the radio core at the base of the M87 jet is the optically thick surface against synchrotron self ...absorption (SSA), observations directly give the size and turnover frequency for SSA. Using the observed angular diameter 0.11 mas, which corresponds to 16 Schwarzschild radii of the central black hole with 6 x 10 super(9) solar mass, and the flux density of the radio core at 43 GHz, we estimate the energy densities of magnetic field (U sub(B) and relativistic electrons (U sub(e) by comparing the standard SSA formula to the observed radio core. Together with the allowed total kinetic power of the M87 jet, we find that (i) the allowed B is limited in the range 2 G < or = B < or = 13 G, and that (ii) 0:18 < or = (U sub(e)(U sub(B)< or = 66 holds. Our results significantly constrain formation mechanism of relativistic jets in active galactic nuclei.
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