1,441 research outputs found
M5-branes and Wilson Surfaces
We investigate the M5-brane description of the Wilson surface operators in
six-dimensional (2,0) superconformal field theory from AdS/CFT correspondence.
We consider the Wilson surface operators in high-dimensional representation,
whose description could be M5-brane string soliton solutions in background. We construct such string soliton solutions from the covariant
M5-brane equations of motion and discuss their properties. The supersymmetry
analysis shows that these solutions are half-BPS. We also discuss the subtle
issue on the boundary terms.Comment: 30 pages, Latex; little revision;Typos corrected, references added,
JHEP published versio
The "amplitude" parameter of Gamma-Ray Bursts and its implications for GRB classification
Traditionally gamma-ray bursts (GRBs) are classified in the -hardness
ratio two-dimensional plane into long/soft and short/hard GRBs. In this paper,
we suggest to add the "amplitude" of GRB prompt emission as the third dimension
as a complementary criterion to classify GRBs, especially those of short
durations. We define three new parameters , and as ratios between the measured/simulated peak flux of a GRB/pseudo-GRB
and the flux background, and discuss the applications of these parameters to
GRB classification. We systematically derive these parameters to find that most
short GRBs are likely not "tip-of-iceberg" of long GRBs. However, one needs to
be cautious if a short GRB has a relatively small (e.g. ), since the
chance for an intrinsically long GRB to appear as a "disguised" short GRB is
higher. Based on avaialble data, we quantify the probability of a disguised
short GRB below a certain value is as . By progressively "moving" a long GRB to higher redshifts
through simulations, we also find that most long GRBs would show up as
rest-frame short GRBs above a certain redshift.Comment: 11 pages, 14 figures. Accepted by MNRA
The electromagnetic and gravitational-wave radiations of X-ray transient CDF-S XT2
Binary neutron star (NS) mergers may result in remnants of supra-massive or
even stable NS, which have been supported indirectly by observed X-ray plateau
of some gamma-ray bursts (GRBs) afterglow. Recently, Xue et al. (2019)
discovered a X-ray transient CDF-S XT2 that is powered by a magnetar from
merger of double NS via X-ray plateau and following stepper phase. However, the
decay slope after the plateau emission is a little bit larger than the
theoretical value of spin-down in electromagnetic (EM) dominated by losing its
rotation energy. In this paper, we assume that the feature of X-ray emission is
caused by a supra-massive magnetar central engine for surviving thousands of
seconds to collapse black hole. Within this scenario, we present the
comparisons of the X-ray plateau luminosity, break time, and the parameters of
magnetar between CDF-S XT2 and other short GRBs with internal plateau samples.
By adopting the collapse time to constrain the equation of state (EOS), we find
that three EOSs (GM1, DD2, and DDME2) are consistent with the observational
data. On the other hand, if the most released rotation energy of magnetar is
dominated by GW radiation, we also constrain the upper limit of ellipticity of
NS for given EOS, and it is range in . Its GW signal
can not be detected by aLIGO or even for more sensitive Einstein Telescope in
the future.Comment: 13 pages, 5 figures,1 table. Accepted for publication by Research in
Astronomy and Astrophysic
Responses of microbial abundance and enzyme activity in integrated vertical-flow constructed wetlands for domestic and secondary wastewater
Although micro-organisms play a significant role in pollutant removal in constructed wetlands, little is known on the effect of wastewater-quality properties on microbial characteristics. In this study, two groups of integrated vertical-flow constructed wetland microcosms were applied to treat synthetic domestic wastewater and synthetic secondary effluent. The effects of wastewater-quality properties on microbial features were assessed. Results showed that higher values of microbial indicators were observed in the systems with domestic wastewater and in down-flow cells. Redundancy analysis revealed that organic matter concentration and temperature were two critical determinants influencing the microbial features
The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?
The first gravitational-wave event from the merger of a binary neutron star system (GW170817) was detected recently. The associated short gamma-ray burst (GRB 170817A) has a low isotropic luminosity (~1047 erg s−1) and a peak energy E p ~ 145 keV during the initial main emission between −0.3 and 0.4 s. The origin of this short GRB is still under debate, but a plausible interpretation is that it is due to the off-axis emission from a structured jet. We consider two possibilities. First, since the best-fit spectral model for the main pulse of GRB 170817A is a cutoff power law with a hard low-energy photon index (), we consider an off-axis photosphere model. We develop a theory of photosphere emission in a structured jet and find that such a model can reproduce a low-energy photon index that is softer than a blackbody through enhancing high-latitude emission. The model can naturally account for the observed spectrum. The best-fit Lorentz factor along the line of sight is ~20, which demands that there is a significant delay between the merger and jet launching. Alternatively, we consider that the emission is produced via synchrotron radiation in an optically thin region in an expanding jet with decreasing magnetic fields. This model does not require a delay of jet launching but demands a larger bulk Lorentz factor along the line of sight. We perform Markov Chain Monte Carlo fitting to the data within the framework of both models and obtain good fitting results in both cases
A Novel Systematic Error Compensation Algorithm Based on Least Squares Support Vector Regression for Star Sensor Image Centroid Estimation
The star centroid estimation is the most important operation, which directly affects the precision of attitude determination for star sensors. This paper presents a theoretical study of the systematic error introduced by the star centroid estimation algorithm. The systematic error is analyzed through a frequency domain approach and numerical simulations. It is shown that the systematic error consists of the approximation error and truncation error which resulted from the discretization approximation and sampling window limitations, respectively. A criterion for choosing the size of the sampling window to reduce the truncation error is given in this paper. The systematic error can be evaluated as a function of the actual star centroid positions under different Gaussian widths of star intensity distribution. In order to eliminate the systematic error, a novel compensation algorithm based on the least squares support vector regression (LSSVR) with Radial Basis Function (RBF) kernel is proposed. Simulation results show that when the compensation algorithm is applied to the 5-pixel star sampling window, the accuracy of star centroid estimation is improved from 0.06 to 6 × 10−5 pixels
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