Solar Flares with an Exponential Growth of the Emission Measure in the Impulsive Phase Derived from X-ray Observations

The light curves of solar flares in the impulsive phase are complex in general, indicating that multiple physical processes are involved in. With the GOES (Geostationary Operational Environmental Satellite) observations, we find that there are a subset of flares, whose impulsive phases are dominated by a period of exponential growth of the emission measure. The flares occurred from January 1999 to December 2002 are analyzed, and the results from the observations made with both GOES 8 and GEOS 10 satellites are compared to estimate the instrumental uncertainties. Their mean temperatures during this exponential growth phase have a normal distribution. Most flares within the 1\sigma\ range of this temperature distribution belong to the GOES class B or C, with the peak fluxes at the GOES low-energy channel following a log-normal distribution. The growth rate and duration of the exponential growth phase also follow a lognormal distribution, in which the duration is distributed in the range from half a minute to about half an hour. As expected, the growth time is correlated with the decay time of the soft X-ray flux. We also find that the growth rate of the emission measure is strongly anti-correlated with the duration of the exponential growth phase, and the mean temperature increases slightly with the increase of the growth rate. The implications of these results on the study of energy release in solar flares are discussed in the end.Comment: 10 figure

Hamiltonian Structures and Reciprocal Transformations for the rr-KdV-CH Hierarchy

The $r$-KdV-CH hierarchy is a generalization of the Korteweg-de Vries and Camassa-Holm hierarchies parametrized by $r+1$ constants. In this paper we clarify some properties of its multi-Hamiltonian structures, prove the semisimplicity of the associated bihamiltonian structures and the formula for their central invariants. By introducing a class of generalized Hamiltonian structures, we give in a natural way the transformation formulae of the Hamiltonian structures of the hierarchy under certain reciprocal transformation, and prove the formulae at the level of its dispersionless limit. We also consider relations of the associated bihamiltonian structures to Frobenius manifolds.Comment: 37 page

Constructing new pseudoscalar meson nonets with the observed X(2100)X(2100), X(2500)X(2500), and η(2225)\eta(2225)

Stimulated by the BESIII observation of $X(2100)$, $X(2500)$, and $\eta(2225)$, we try to pin down new pseudoscalar meson nonets including these states. The analysis of mass spectra and the study of strong decays indicate that $X(2120)$ and $\eta(2225)$ associated with $\pi(2070)$ and the predicted kaon $K(2150)$ may form a new pseudoscalar meson nonet. In addition, more experimental data for $X(2100)$ are necessary to determine its structure of nonets. Then, $X(2500)$, $X(2370)$, $\pi(2360)$, and the predicted kaon $K(2414)$ can be grouped into another new nonet. These assignments to the discussed pseudoscalar states can be further tested in experiment.Comment: 15 pages, 4 tables and 10 figures. More discussions added and typos corrected. Accepted by Phys. Rev.

A GeV source in the direction of Supernova Remnant CTB 37B

Supernova remnants (SNRs) are the most attractive candidates for the acceleration sites of Galactic cosmic rays. We report the detection of GeV $\gamma$-ray emission with the Pass 8 events recorded by Fermi Large Area Telescope (Fermi-LAT) in the vicinity of the shell type SNR CTB 37B that is likely associated with the TeV $\gamma-$ray source HESS J1713-381. The photon spectrum of CTB 37B is consistent with a power-law with an index of $1.89\pm0.08$ in the energy range of $0.5-500$ GeV, and the measured flux connects smoothly with that of HESS J1713-381 at a few hundred GeV. No significant spatial extension and time variation are detected. The multi-wavelength data can be well fitted with either a leptonic model or a hadronic one. However, parameters of both models suggest more efficient particle acceleration than typical SNRs. Meanwhile, the X-ray and $\gamma$-ray spectral properties of CTB 37B show that it is an interesting source bridging young SNRs dominated by non-thermal emission and old SNRs interacting with molecular clouds.Comment: 6 pages, 5 figures, 2 tables, published in ApJ, 817, 6

The SNR Puppis A Revisited with Seven Years of Fermi Large Area Telescope Observations

Puppis A is a very famous and extensively studied supernova remnant (SNR) that shows strong evidence of shock-cloud interaction. We re-analyze the GeV $\gamma$-ray emission of it using seven years Pass 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT). The morphology of the $\gamma$-ray emission is more compatible with that of the thermal X-ray and IR emissions than the radio image, which suggests a possible correlation between the gamma-ray emitting region and dense clouds. The $\gamma$-ray spectrum in the energy range of 1-500 GeV shows a break at $7.92\pm1.91$ GeV with the photon indices of $1.81\pm0.08$ below the break and $2.53\pm0.12$ above the break, which can naturally explain the lack of TeV $\gamma$-ray emission from Puppis A. The multi-wavelength observations favor a hadronic origin for the $\gamma$-ray emission.Comment: 9 pages, 4 figures, 4 tables, Accepted for publication in Ap

Studying X(2100)X(2100) hadronic decays and predicting its pion and kaon induced productions

The newly observed $X(2100)$ by the BESIII Collaboration inspires our interest in studying the light meson system, especially axial-vector mesons. Since the $X(2100)$ has $J^P=1^+$ possibilities but cannot be distinguished only by mass, we make use of flux-tube model to study the strong decay behavior of $X(2100)$ under this assignment. The experimental width of the newly reported $X(2100)$ can be reproduced in our calculation, which favors an assignment of $X(2100)$ as the second radial excitation of $h_1(1380)$ with $I(J^P)=0(1^+)$. And the $\mathcal{B}(X(2100)\to \phi \eta^\prime)$ has a sizable contribution to the total width. Furthermore, we focus on the production of $X(2100)$ and its flavour partner $h_1(1965)$ induced by pion and kaon on a proton target with the Feynman model and the Regge model, which is an available platform to further identify their nature. The numerical results indicate that the total cross section are similar in the two models. When the range of momentum ${\mathrm{p_{Lab}}}$ is 10 to 30 GeV/$c$, the total cross sections for $\pi^-p\to X(2100)n$ and $K^-p\to X(2100)\Lambda$ are predicted to be at an order of magnitude of 0.1 $\mu$b. Whereas, the total cross section for $\pi^-p\to h_1(1965)n$ is near an order of magnitude of 10 $\mu$b when $p_{\mathrm{Lab}}$ is from 10 to 30 GeV/$c$, and much larger than that of reaction $K^-p\to h_1(1965)\Lambda$. These predictions can provide some valuable information to search for $X(2100)$ and $h_1(1965)$ in experiments at J-PARC, COMPASS, OKA@U-70 and [email protected]: 9 pages and 8 figures. Accepted by Phys. Rev. D for publicatio

Almost ideal nodal-loop semimetal in monoclinic CuTeO3_3 material

Nodal-loop semimetals are materials in which the conduction and valence bands cross on a one-dimensional loop in the reciprocal space. For the nodal-loop character to manifest in physical properties, it is desired that the loop is close to the Fermi level, relatively flat in energy, simple in its shape, and not coexisting with other extraneous bands. Here, based on the first-principles calculations, we show that the monoclinic CuTeO$_3$ is a realistic nodal-loop semimetal that satisfies all these requirements. The material features only a single nodal loop around the Fermi level, protected by either of the two independent symmetries: the $\mathcal{PT}$ symmetry and the glide mirror symmetry. The size of the loop can be effectively tuned by strain, and the loop can even be annihilated under stain, making a topological phase transition to a trivial insulator phase. Including the spin-orbit coupling opens a tiny gap at the loop, and the system becomes a $\mathbb{Z}_2$ topological semimetal with a nontrivial bulk $\mathbb{Z}_2$ invariant but no global bandgap. The corresponding topological surface states have been identified. We also construct a low-energy effective model to describe the nodal loop and the effect of spin-orbit coupling.Comment: 8 pages, 10 figure

General monogamy property of global quantum discord and the application

We provide a family of general monogamy inequalities for global quantum discord (GQD), which can be considered as an extension of the usual discord monogamy inequality. It can be shown that those inequalities are satisfied under the similar condition for the holding of usual monogamy relation. We find that there is an intrinsic connection among them. Furthermore, we present a different type of monogamy inequality and prove that it holds under the condition that the bipartite GQDs do not increase when tracing out some subsystems. We also study the residual GQD based on the second type of monogamy inequality. As applications of those quantities, we investigate the GQDs and residual GQD in characterizing the quantum phase transition in the transverse field Ising model.Comment: 11 pages, 6 figure

Statistical properties of radio flux densities of solar flares

Short timescale flux variations are closely related to the energy release process of magnetic reconnection during solar flares. Radio light curves at 1, 2, 3.75, 9.4, and 17 GHz of 209 flares observed by the Nobeyama Radio Polarimeter from 2000 to 2010 are analyzed with a running smooth technique. We find that the impulsive component (with a variation timescale shorter than 1 second) of 1 GHz emission of most flares peaks at a few tens of solar flux unit and lasts for about 1 minute and the impulsive component of 2 GHz emission lasts a shorter period and peaks at a lower flux level, while at the three high frequency channels the occurrence frequency of flares increases with the decrease of the flux density up to the noise level of the corresponding background. The gradual components of these emissions, however, have similar duration and peak flux density distributions. We also derive the power spectrum on different timescales and a normalized wavelet analysis is used to confirm features on short timescales. At a time resolution of 0.1 second, more than $\sim$ 60$\%$ of these radio light curves show significant flux variation on 1 second or shorter time scales. This fraction increases with the decrease of frequency and reaches $\sim$ 100$\%$ at 1 GHz, implying that short timescale processes are universal in solar flares. We also study the correlation between the impulsive radio flux densities and soft X-ray fluxes obtained with the GOES satellites and find that more than 65$\%$ of the flares with an impulsive component have their impulsive radio emission reach a peak value ahead of the soft X-ray fluxes and this fraction increases with the radio frequency

Detecting degeneracy and subtle broken-symmetry states of graphene at nanoscale

Measuring degeneracy and broken-symmetry states of a system at nanoscale requires extremely high energy and spatial resolution, which has so far eluded direct observation. Here, we realize measurement of the degeneracy and subtle broken-symmetry states of graphene at nanoscale for the first time. By using edge-free graphene quantum dots, we are able to measure valley splitting and valley-contrasting spin splitting of graphene at the single-electron level. Our experiments detect large valley splitting around atomic defects of graphene due to the coexistence of sublattice symmetry breaking and time reversal symmetry breaking. Large valley-contrasting spin splitting induced by enhanced spin-orbit coupling around the defects is also observed. These results reveal unexplored exotic electronic states in graphene at nanoscale induced by the atomic defects.Comment: 4 figures in main tex