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Using a sample of 13 early-type spiral galaxies hosting nuclear rings, we report remarkable correlations between the properties of the nuclear rings and the central intensity ratio (CIR) of their host galaxies. The CIR, a function of intensity of light within the central 1.5 and 3 arcsec region, is found to be a vital parameter in galaxy evolution, as it shares strong correlations with many structural and dynamical properties of early-type galaxies, including mass of the central supermassive black hole (SMBH). We use archival HST images for aperture photometry at the centre of the galaxy image to compute the CIR. We observe that the relative sizes of nuclear rings and ring cluster surface densities strongly correlate with the CIR. These correlations suggest reduced star formation in the centres of galaxies hosting small and dense nuclear rings. This scenario appears to be a consequence of strong bars as advocated by the significant connection observed between the CIR and bar strengths. In addition, we observe that the CIR is closely related with the integrated properties of the stellar population in the nuclear rings, associating the rings hosting older and less massive star clusters with low values of CIR. Thus, the CIR can serve as a crucial parameter in unfolding the coupled evolution of bars and rings as it is intimately connected with both their properties.

The kinematical parameters, spatial shape and structure of the open cluster IC 2391 and the associated stellar stream are studied here using Gaia Data Release 2 (GDR2) astrometry data. The apex positions are determined for the open cluster IC 2391 (data taken from Cantat-Gaudin et al.) and for the kinematical stream's stars mentioned in Montes et al. employing both convergent point and AD-diagram methods. The values of apex coordinates are: (A, D)_CP = (${6}_{.}^{{\rm{h}}}17\pm {0}_{.}^{{\rm{h}}}004,-{6}_{.}^{^\circ }88\pm {0}_{.}^{^\circ }381$; for cluster) and (${6}_{.}^{{\rm{h}}}07\pm {0}_{.}^{{\rm{h}}}007$, $-{5}_{.}^{^\circ }00\pm {0}_{.}^{^\circ }447$; stream), and (A₀, D₀) = (${6}_{.}^{{\rm{h}}}12\pm {0}_{.}^{{\rm{h}}}004$, $-{3}_{.}^{^\circ }4\pm {0}_{.}^{^\circ }3$; cluster) and (${6}_{.}^{{\rm{h}}}21\pm {0}_{.}^{{\rm{h}}}007$, $-{11}_{.}^{^\circ }895\pm {0}_{.}^{^\circ }290$; stream). The results are in good agreement with the previously calculated values. The positions of the stars in the disk and the spatial dispersion velocities are determined. The paths of cluster and associated stream are traced in the disk by orbit calculation back in time to their places of formation. A possible genetic relationship between the cluster and stream has been detected. The approximation of the spatial and kinematical shape of the stream and the cluster is made. According to this study, even though currently the cluster and stream seem to have a spatial difference in their locations, they appear to have formed in the same region of the Galactic disk.

A 200-second X-ray quasi-periodicity in the 2 – 8 keV band from Swift J1644+57 was found by Reis et al. From the onset time of quasi-periodic oscillation (QPO), we show that Swift J1644+57 is a plunging event. This QPO may be related to discrete clumps from the accretion disk falling into a supermassive black hole, then the outflow in the jet may be also discontinuous. We estimate the lifetime of clumps to be about several hundreds seconds and the fraction of clumpy ejecta to be about 30% from the QPO. The other possible model involves the interface between the inflow and jet magnetosphere in the magnetically choked accretion flow. Theory and numerical simulations indicate that a magnetic Rayleigh-Taylor and Kelvin-Helmholtz unstable magnetospheric interface can produce a jet-disk QPO mechanism. This event may be the first evidence of jet-disk QPO. From observations, the two models are comparable.

During non-flaring times, the radio flux of the Sun at wavelengths of a few centimeters to several tens of centimeters mostly originates from thermal bremsstrahlung emission, very similar to extremeultraviolet (EUV) radiation. Owing to such a proximity, it is feasible to investigate the relationship between the EUV emission and radio emission in a quantitative way. In this paper, we reconstruct the radio images of the Sun through the differential emission measure obtained from multi-wavelength EUV images of the Atmospheric Imaging Assembly on board Solar Dynamics Observatory (SDO). Through comparing the synthetic radio images at 6GHz with those observed by the Siberian Radioheliograph, we find that the predicted radio flux is qualitatively consistent with the observed value, confirming thermal origin of the coronal radio emission during non-flaring times. The results further show that the predicted radio flux is closer to the observations in the case that includes the contribution of plasma with temperatures above 3MK than in the case of only involving low temperature plasma, as was usually done in the pre-SDO era. We also discuss applications of the method and uncertainties of the results.

One of the most efficient ways to probe the lunar inner structure at present is through the study of its rotation. Range and range rate (Doppler) data between the Chang'E-3 lander and station on the Earth were collected from the beginning of the Chang'E-3 lunar mission in 2013. These observation data, taken together with the existing lunar laser ranging data, provide a new approach to extend research on the Earth-Moon system. The high precision of current observation data imposes exacting demands, making it necessary to include previously neglected factors. In this paper, motivated by progress of the Chinese lunar exploration project and to use its data in the near future, two lunar models: a one-layer model and a two-layer model with a fluid core, were applied to the rotational equations based on our implemented algorithm of the Moon's motion. There was a difference of about 0.5'' in ϕ and ψ, but 0.2'' in θ between the two models. This result confirms that stratification of the inner structure of the Moon can be inferred from rotation data. We also added precise Earth rotation parameters in our model; the results show that this factor is negligible at present, due to the limited precision of the existing data. These results will help us understand the rotational process clearly and build a more realistic Earth-Moon model when we combine Lunar Laser Ranging data with high precision radio data to fit lunar motion in the near future.

We use 1221 galaxies with unusually high gas-phase metallicity to study their physical properties. The scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase metallicity. Our goal is to understand the physical origins of the high gas-phase metallicity. To address this study, we select a control sample matching similar redshift and stellar mass. Our main results are as follows. (i) Compared with the control sample, the high-metallicity sample shows lower ionization parameter, higher electron density and more dust content. (ii) We also find that the high-metallicity sample has older stellar age and higher [Mgb/<Fe>] ratio, which indicates that the high-metallicity sample has shorter timescale of star formation. (iii) According to the plane of Hδ_A vs. D_n4000, we can see that the control sample has higher Hδ_A and lower D_n4000 than the high-metallicity sample, which may imply that the control sample experiences recent star formation. (iv) There is a significant difference in gas distribution between the high-metallicity and control samples. The high-metallicity sample has lower gas fraction than control sample, which indicates that galaxies have high gas-phase metallicity probably due to their low HI gas fraction. (v) There is no significant difference between the high-metallicity and control samples in environment, which may suggest that the environment has no effect on gas-phase metallicity.

Based on the Seventh Data Release (DR7) quasar catalog from the Sloan Digital Sky Survey, we investigate the variability of optical quasars in W1, W2, W3 and W4 bands of the Wide-field Infrared Survey Explorer (WISE) and the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE). Adopting the structure function (SF) method, we calculate the SF (δ t = 1 yr) which shows no obvious correlations with the bolometric luminosity, the black hole mass and the Eddington ratio. The ensemble SFs in W1 and W2 bands show that the SF slopes are steeper than those in previous studies which may be caused by different cadence and observational epoch number. We further investigate the relation of variability amplitude σ_m between mid-infrared band and optical band, but no obvious correlation is found. No correlation is found between W1–W2 and g – r color. We think that the mid-infrared emission of quasars may be smoothed out by the extended dust distribution, thus leading to no obvious correlation. For the radio-loud quasar sub-sample, we further analyze the relation between the variability amplitude in the mid-infrared band and the radio luminosity at 6 cm, but no obvious correlations are found, which indicate the mid-infrared emission contributed from the synchrotron radiation of the relativistic jet is very weak.

Studies on the periodic variation and the phase relationship between different solar activity indicators are useful for understanding the long-term evolution of solar activity cycles. Here we report the statistical analysis of grouped solar flare (GSF) and sunspot number (SN) during the time interval from January 1965 to March 2009. We find that, (1) the significant periodicities of both GSF and SN are related to the differential rotation periodicity, the quasi-biennial oscillation (QBO), and the eleven-year Schwabe cycle (ESC), but the specific values are not absolutely identical; (2) the ESC signal of GSF lags behind that of SN with an average of 7.8 months during the considered time interval, which implies that the systematic phase delays between GSF and SN originate from the inter-solar-cycle signal. Our results may provide evidence about the storage of magnetic energy in the corona.

In this reported work, we study a major X-class flare (X9.3) that arose from NOAA Active Region (AR) 12673 on 2017 September 6, from 11:53 UT to 12:10 UT in multi-wavelength views. This event also produced a fast coronal mass ejection (CME). NOAA AR 12673 emerged at S09W30 on 2017 September 6 and grew rapidly to a large AR. On 2017 September 9, the maximum area of this AR was 1060 millionth of the solar hemisphere. The group of sunspots disappeared over the west limb of the Sun (S09W83) on September 10. It was a fast emerging flux region. The group of sunspots showed magnetic configuration category alpha-beta-gamma. We identified their earliest signatures of eruption in AIA 94 Å images with initialization and successive rapid growth from low coronal heights of hot channeled structures. On the other hand, the CME associated with this flare event triggered the intense Dst at 1AU (−142nT). We have acquired observations and analyze the reported event from the Sun's surface, corona (source AR), interplanetary space and in-situ measurement near Earth. In addition, here we analyze the complex processes of CME-CME interaction that have contributed a significant role to make the reported event so geoeffective.

I present a novel mechanism to boost magnetic field amplification of newly born neutron stars in core collapse supernovae. In this mechanism, that operates in the jittering jets explosion mechanism and comes on top of the regular magnetic field amplification by turbulence, the accretion of stochastic angular momentum in core collapse supernovae forms a neutron star with strong initial magnetic fields but with a slow rotation. The varying angular momentum of the accreted gas, which is unique to the jittering jets explosion mechanism, exerts a varying azimuthal shear on the magnetic fields of the accreted mass near the surface of the neutron star. This, I argue, can form an amplifying effect which I term the stochastic omega (Sω) effect. In the common αω dynamo the rotation has constant direction and value, and hence supplies a constant azimuthal shear, while the convection has a stochastic behavior. In the Sω dynamo the stochastic angular momentum is different from turbulence in that it operates on a large scale, and it is different from a regular rotational shear in being stochastic. The basic assumption is that because of the varying direction of the angular momentum axis from one accretion episode to the next, the rotational flow of an accretion episode stretches the magnetic fields that were amplified in the previous episode. I estimate the amplification factor of the Sω dynamo alone to be ≈ 10. I speculate that the Sω effect accounts for a recent finding that many neutron stars are born with strong magnetic fields.

Active galactic nuclei (AGNs) can be divided into two major classes, namely radio-loud and radio-quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which are believed to be unified with Fanaroff-Riley type I and type II (FRI&II) radio galaxies. Following our previous work, we present a latest sample of 966 sources with measured radio flux densities of the core and extended components. The sample includes 83 BL Lacs, 473 flat spectrum radio quasars, 101 Seyferts, 245 galaxies, 52 FRIs&IIs and 12 unidentified sources. We then calculate the radio core-dominance parameters and spectral indices and study their relationship. Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources. We also confirm that the correlation between core-dominance parameter and radio spectral index extends over all the sources in a large sample presented.

We propose a magnetic confinement nuclear fusion mechanism for the evolution of a solar flare in the solar atmosphere. The mechanism agrees with two observed characteristics of explosive flares and coronal mass ejections (CMEs) that have proved to be very difficult to explain with previous mechanisms: the huge enrichments of ³He and the high energy gamma ray radiation. The twisted magnetic flux rope is a typical structure during the solar flares, which is closely related to the solar active region that magnetic fields have almost complete control over the plasma. Consequently, the plasma inside the flux rope is heated to more than 1.0 × 10⁷ K by an adiabatic compression process, and then the thermonuclear fusion can take place in the flux rope accompanied with high energy gamma rays. We utilize the time-dependent ideal 2.5-dimensional magnetohydrodynamic (MHD) simulation to demonstrate the physical mechanism for producing flares, which reveals three stages of flare development with the process of magnetic energy conversion and intense release during the solar flares and CMEs in the solar atmosphere. Furthermore, we discuss the relationship between magnetic reconnection and solar eruptions.

By appealing to a quark nova (QN; the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova (CCSN) explosion of a massive star, we develop a unified model for long duration gamma-ray bursts (LGRBs) and fast radio bursts (FRBs). The time delay (years to decades) between the SN and the QN, and the fragmented nature (i.e., millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine. In our model, an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent (i.e., filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula (PWN). The afterglow is due to the interaction of the QN chunks, exiting the SN ejecta, with the surrounding medium. Our model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra, thus yielding the observed properties of LGRBs (e.g., the Band function and the X-ray flares). We find that the peak luminositypeak photon energy relationship (i.e., the Yonetoku law), and the isotropic energy-peak photon energy relationship (i.e., the Amati law) are not fundamental but phenomenological. FRB-like emission in our model results from coherent synchrotron emission (CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta, where conditions are prone to the Weibel instability. Magnetic field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate coherently. The resulting emission frequency, luminosity and duration in our model are consistent with FRB data. We find a natural unification of high-energy burst phenomena from FRBs (i.e., those connected to CCSNe) to LGRBs including X-ray flashes (XRFs) and X-ray rich GRBs (XRR-GRBs) as well as superluminous SNe (SLSNe). We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yield a short duration GRB (SGRB) with fits to BAT/XRT light curves.