Search

Active galaxies, especially blazars, are among the most promising extragalactic candidates for high-energy neutrino sources. To date, ANTARES searches included these objects and used GeV–TeV γ -ray flux to select blazars. Here, a statistically complete blazar sample selected by their bright radio emission is used as the target for searches of origins of neutrinos collected by the ANTARES neutrino telescope over 13 yr of operation. The hypothesis of a neutrino–blazar directional correlation is tested by pair counting and a complementary likelihood-based approach. The resulting posttrial p -value is 3.0% (2.2 σ in the two-sided convention). Additionally, a time-dependent analysis is performed to search for temporal clustering of neutrino candidates as a means of detecting neutrino flares in blazars. None of the investigated sources alone reaches a significant flare detection level. However, the presence of 18 sources with a pretrial significance above 3 σ indicates a p = 1.4% (2.5 σ in the two-sided convention) detection of a time-variable neutrino flux. An a posteriori investigation reveals an intriguing temporal coincidence of neutrino, radio, and γ -ray flares of the J0242+1101 blazar at a p = 0.5% (2.9 σ in the two-sided convention) level. Altogether, the results presented here suggest a possible connection of neutrino candidates detected by the ANTARES telescope with radio-bright blazars.

Whereas light-element abundance variations are a hallmark of globular clusters, there is little evidence for variations in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-capture dispersion in M92. We conducted an analysis of archival Keck/HIRES spectra of 35 stars in M92, 29 of which are giants, which we use exclusively for our conclusions. M92 conforms to the abundance variations typical of massive clusters. Like other globular clusters, its neutron-capture abundances were generated by the r -process. We confirm a star-to-star dispersion in r -process abundances. Unlike M15, the dispersion is limited to “first-generation” (low-Na, high-Mg) stars, and the dispersion is smaller for Sr, Y, and Zr than for Ba and the lanthanides. This is the first detection of a relation between light-element and neutron-capture abundances in a globular cluster. We propose that a source of the main r -process polluted the cluster shortly before or concurrently with the first generation of star formation. The heavier r -process abundances were inhomogeneously distributed while the first-generation stars were forming. The second-generation stars formed after several crossing times (∼0.8 Myr); hence, the second generation shows no r -process dispersion. This scenario imposes a minimum temporal separation of 0.8 Myr between the first and second generations.

We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected ( u , v ) spacings up to ∼11 G λ . The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013–2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 G λ . For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 G λ baseline lengths, resulting in a new image with angular resolution of ∼150 μ as or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds ${T}_{{\rm{B}},\min }\sim {10}^{12}\,$ K. It is challenging to explain the origin of this record-high ${T}_{{\rm{B}},\min }$ value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.

We develop a theory of the magnetoplasmon resonance (MPR) in two-dimensional superconductors in the fluctuating regime, where the temperature is slightly above the critical temperature of the superconducting transition. In this regime, unpaired electrons and fluctuating Cooper pairs coexist in the system and interact with each other via long-range Coulomb forces, forming a Bose–Fermi mixture. The sample is considered to be under the influence of an external time-dependent electromagnetic field with a frequency in sub-terahertz range and a permanent magnetic field. It is shown that the MPR of the system is strongly modified in the presence of superconducting fluctuations in the vicinity of the superconducting transition. In particular, the fluctuating Cooper pairs dramatically change the broadening of the MPR, which is reflected in the optical response of the system.

We report on a novel mechanism of BCS-like superconductivity, mediated by a pair of Bogoliubov quasiparticles (bogolons). It takes place in hybrid systems consisting of a two-dimensional electron gas in a transition metal dichalcogenide monolayer in the vicinity of a Bose–Einstein condensate. Taking a system of two-dimensional indirect excitons as a testing ground of Bose-Einstein condensate we show, that the bogolon-pair-mediated electron pairing mechanism is stronger than phonon-mediated and single bogolon-mediated ones. We develop a microscopic theory of bogolon-pair-mediated superconductivity, based on the Schrieffer–Wolff transformation and the Gor’kov’s equations, study the temperature dependence of the superconducting gap and estimate the critical temperature of superconducting transition for various electron concentrations in the electron gas and the condensate densities.

We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (u, v) spacings up to ∼11 G λ. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013–2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 G λ. For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 G λ baseline lengths, resulting in a new image with angular resolution of ∼150 μ as or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds T B , min ∼ 10 12 K. It is challenging to explain the origin of this record-high T B , min value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow. [ABSTRACT FROM AUTHOR]