An hourglass model for the flare of HST-1 in M87

To explain the multi-wavelength light curves (from radio to X-ray) of HST-1 in the M87 jet, we propose an hourglass model that is a modified two-zone system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or Laval nozzle-shaped layer connected by two revolving exponential surfaces surrounding a fast spine, through which plasma blobs flow. Based on the conservation of magnetic flux, the magnetic field changes along the axis of the hourglass. We adopt the result of TG08---the high-energy emission from GeV to TeV can be produced through inverse Compton by the two-zone system, and the photons from radio to X-ray are mainly radiated by the fast inner zone system. Here, we only discuss the light curves of the fast inner blob from radio to X-ray. When a compressible blob travels down the axis of the first bulb in the hourglass, because of magnetic flux conservation, its cross section experiences an adiabatic compression process, which results in particle acceleration and the brightening of HST-1. When the blob moves into the second bulb of the hourglass, because of magnetic flux conservation, the dimming of the knot occurs along with an adiabatic expansion of its cross section. A similar broken exponential function could fit the TeV peaks in M87, which may imply a correlation between the TeV flares of M87 and the light curves from radio to X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1 verifies our prediction based on the model fit to the main peak of the VLA 15 GHz radio light curve.Comment: 14 pages, 2 figures, accepted for publication in A

Hidden Real Topology and Unusual Magnetoelectric Responses in Monolayer Antiferromagnetic Cr2_2Se2_2O

Recently, the real topology has been attracting widespread interest in two dimensions (2D). Here, based on first-principles calculations and theoretical analysis, we reveal the monolayer Cr$_2$Se$_2$O (ML-CrSeO) as the first material example of a 2D antiferromagnetic (AFM) real Chern insulator (RCI) with topologically protected corner states. Unlike previous RCIs, we find that the real topology of the ML-CrSeO is rooted in one certain mirror subsystem of the two spin channels, and can not be directly obtained from all the valence bands in each spin channel as commonly believed. In particular, due to antiferromagnetism, the corner modes in ML-CrSeO exhibit strong corner-contrasted spin polarization, leading to spin-corner coupling (SCC). This SCC enables a direct connection between spin space and real space. Consequently, large and switchable net magnetization can be induced in the ML-CrSeO nanodisk by electrostatic means, such as potential step and in-plane electric field, and the corresponding magnetoelectric responses behave like a sign function, distinguished from that of the conventional multiferroic materials. Our work considerably broadens the candidate range of RCI materials, and opens up a new direction for topo-spintronics and 2D AFM materials research

catena-Poly[(dichloridozinc)-μ-1-{4-[(1H-imidazol-1-yl)meth­yl]benz­yl}-1H-imidazole-κ2 N 3:N 3′]

The asymmetric unit of the title compound, [ZnCl2(C14H14N4)]n, contains a ZnII ion situated on a twofold rotation axis and one-half of a 1-{4-[(1H-imidazol-1-yl)meth­yl]benz­yl}-1H-imidazole (L) ligand with the benzene ring situated on an inversion center. The ZnII ion is coordinated by two chloride anions and two N atoms from two L ligands in a distorted tetra­hedral geometry. The L ligands bridge ZnCl2 fragments into polymeric chains parallel to [20-1]

catena-Poly[(dichloridozinc)-μ-4,4′-bis­[(1H-imidazol-1-yl)meth­yl]biphenyl-κ2 N 3:N 3′]

In the title compound, [ZnCl2(C20H18N4)]n, the ZnII ion lies on a twofold rotation axis and is four-coordinated in a tetra­hedral geometry defined by two Cl anions and two N atoms from two 4,4′-bis­[(imidazol-1-yl)meth­yl]biphenyl ligands. The mid-point of the ligand is located on an inversion center, and shows a trans conformation. The ligands link the ZnII ions, forming a chain structure along [10-1]