arXiv subjects

Bin Chen

Publications and source records attributed to Bin Chen.

At least 739 records · Page 41Linked to original sources

arXiv2012

Further Evidence that Quasar X-Ray Emitting Regions Are Compact: X-Ray and Optical Microlensing in the Lensed Quasar Q J0158-4325

We present four new seasons of optical monitoring data and six epochs of X-ray photometry for the doubly-imaged lensed quasar Q J0158-4325. The high-amplitude, short-period microlensing variability for which this system is known has historically precluded a time delay measurement by conventional methods. We attempt to circumvent this limitation by application of a Monte Carlo microlensing analysis technique, but we are only able to prove that the delay must have the expected sign (image A leads image B). Despite our failure to robustly measure the time delay, we successfully model the microlensing at optical and X-ray wavelengths to find a half light radius for soft X-ray emission log(r_{1/2,X,soft}/cm) = 14.3^{+0.4}_{-0.5}, an upper limit on the half-light radius for hard X-ray emission log(r_{1/2,X,hard}/cm) <= 14.6 and a refined estimate of the inclination-corrected scale radius of the optical R-band (rest frame 3100 Angstrom) continuum emission region of log(r_s/cm) = 15.6+-0.3.

astro-ph.CO↗

arXiv2012

A New Exponential Gravity

We propose a new exponential f(R) gravity model with f(R)=(R-λc)e^{λ(c/R)^n} and n>3, λ\geq 1, c>0 to explain late-time acceleration of the universe. At the high curvature region, the model behaves like the \LambdaCDM model. In the asymptotic future, it reaches a stable de-Sitter spacetime. It is a cosmologically viable model and can evade the local gravity constraints easily. This model share many features with other f(R) dark energy models like Hu-Sawicki model and Exponential gravity model. In it the dark energy equation of state is of an oscillating form and can cross phantom divide line ω_{de}=-1. In particular, in the parameter range 3< n\leq 4, λ\sim 1, the model is most distinguishable from other models. For instance, when n=4, λ=1, the dark energy equation of state will cross -1 in the earlier future and has a stronger oscillating form than the other models, the dark energy density in asymptotical future is smaller than the one in the high curvature region. This new model can evade the local gravity tests easily when n>3 and λ>1.

astro-ph.CO↗

arXiv2012

The Role of Inverse Compton Scattering in Solar Coronal Hard X-ray and Gamma-ray Sources

Coronal hard X-ray (HXR) and continuum gamma-ray sources associated with the impulsive phase of solar flares have been the subject of renewed interest in recent years. They have been interpreted in terms of thin-target, nonthermal bremsstrahlung emission. This interpretation has led to rather extreme physical requirements in some cases. For example, in one case, essentially all of the electrons in the source must be accelerated to nonthermal energies to account for the coronal HXR source. In other cases, the extremely hard photon spectra of the coronal continuum gamma-ray emission suggest that the low energy cutoff of the electron energy distribution lies in the MeV energy range. Here we consider the role of inverse Compton scattering (ICS) as an alternate emission mechanism in both the ultra- and mildly relativistic regimes. It is known that relativistic electrons are produced during powerful flares; these are capable of up-scattering soft photospheric photons to HXR and gamma-ray energies. Previously overlooked is the fact that mildly relativistic electrons, generally produced in much greater numbers in flares of all sizes, can up-scatter EUV/SXR photons to HXR energies. We also explore ICS on anisotropic electron distributions and show that the resulting emission can be significantly enhanced over an isotropic electron distribution for favorable viewing geometries. We briefly review results from bremsstrahlung emission and reconsider circumstances under which nonthermal bremsstrahlung or ICS would be favored. Finally, we consider a selection of coronal HXR and gamma-ray events and find that in some cases the ICS is a viable alternative emission mechanism.

astro-ph.SR↗

arXiv2012

X-ray Monitoring of Gravitational Lenses With Chandra

We present \emph{Chandra} monitoring data for six gravitationally lensed quasars: QJ 0158$-$4325, HE 0435$-$1223, HE 1104$-$1805, SDSS 0924+0219, SDSS 1004+4112, and Q 2237+0305. We detect X-ray microlensing variability in all six lenses with high confidence. We detect energy dependent microlensing in HE 0435$-$1223, SDSS 1004+4112, SDSS 0924+0219 and Q 2237+0305. We present a detailed spectral analysis for each lens, and find that simple power-law models plus Gaussian emission lines give good fits to the spectra. We detect intrinsic spectral variability in two epochs of Q 2237+0305. We detect differential absorption between images in four lenses. We also detect the \feka\ emission line in all six lenses, and the Ni XXVII K$α$ line in two images of Q 2237+0305. The rest frame equivalent widths of the \feka\ lines are measured to be 0.4--1.2 keV, significantly higher than those measured in typical active galactic nuclei of similar X-ray luminosities. This suggests that the \feka\ emission region is more compact or centrally concentrated than the continuum emission region.

astro-ph.HE↗

arXiv2012

Notes on Self-dual Warped dS$_3$ Spacetime

In this paper, we investigate the warped dS/CFT correspondence of the self-dual warped dS$_3$ spacetime, which is a solution of three-dimensional topologically massive gravity (TMG) with a positive cosmological constant. We discuss its thermodynamics at two cosmological horizons. We propose that the self-dual warped dS$_3$ spacetime is holographically dual to a chiral conformal field theory. We analytically calculate the quasinormal modes of scalar, vector, tensor, and spinor perturbations under the self-dual warped dS$_3$ spacetime. It turns out that the frequencies of the quasinormal modes could be identified with the poles in the thermal boundary-boundary correlators.

hep-th↗

arXiv2011

Quasinormal Modes and Hidden Conformal Symmetry of Warped dS$_3$ Black Hole

In this paper, we analytically calculate the quasinormal modes of scalar, vector, tensor, and spinor perturbations of the warped dS$_3$ black hole. There are two horizons for the warped dS$_3$ black hole, namely, the black hole horizon $r_b$ and the cosmological horizon $r_c$. In the calculation, we impose the ingoing boundary condition at the black hole horizon and the outgoing boundary condition at the cosmological horizon. We also investigate the hidden conformal symmetry of the warped dS$_3$ black hole in the region between the black hole horizon and the cosmological horizon $r_b<r<r_c$. We use the hidden conformal symmetry to construct the quasinormal modes in an algebraic way and find that the results agree with the analytically ones. It turns out that the frequencies of the quasinormal modes could be identified with the poles in the thermal boundary-boundary correlators.

hep-th↗

arXiv2011

High Spin Topologically Massive Gravity

We propose an action to describe high spin topologically massive gravity with a negative cosmological constant. With the frame-like fields and spin connections being combined into two gauge fields, the action includes two gauge field Chern-Simons actions with different levels, and also a linear term proportional to the difference of the gauge field strengths. Such linear term play the role of imposing the torsion free conditions for high spin fields. We discuss the gauge symmetry of this action and study the fluctuations around the AdS$_3$ vacuum. We show how to relate the the fluctuations of the gauge field to the Frondal fields, using the gauge symmetry. For the gauge group $SL(n,R)\times SL(n,R)$, we find that the fluctuations of all high spin fields up to spin $n$ satisfy third order differential equations, and hence there generically exist massive traceless and trace mode for every spin.

hep-th↗

arXiv2011

General Hidden Conformal Symmetry of 4D Kerr-Newman and 5D Kerr Black Holes

There are two known CFT duals, namely the J-picture and the Q-picture, for a four-dimensional Kerr-Newman black hole, corresponding to the angular momentum $J$ and the electric charge $Q$ respectively. In our recent study we found a one-parameter class of CFT duals for extremal Kerr-Newman black hole, connecting these two pictures. In this paper we study these novel CFT duals for the generic non-extremal Kerr-Newman black hole. We investigate the hidden conformal symmetry in the low frequency scattering off Kerr-Newman black hole, from which the dual temperatures could be read. We find that there still exists a hidden conformal symmetry for a general CFT dual. We reproduce the correct Bekenstein-Hawking entropy from the Cardy formula, assuming the form of the central charge being invariant. Moreover we compute the retarded Green's function in the general CFT dual picture and find it is in good match with the CFT prediction. Furthermore we discuss the hidden conformal symmetries of the five dimensional Kerr black hole and obtain the similar evidence to support the general dual CFT pictures.

hep-th↗

arXiv2011

Novel CFT Duals for Extreme Black Holes

In this paper, we study the CFT duals for extreme black holes in the stretched horizon formalism. We consider the extremal RN, Kerr-Newman-AdS-dS, as well as the higher dimensional Kerr-AdS-dS black holes. In all these cases, we reproduce the well-established CFT duals. Actually we show that for stationary extreme black holes, the stretched horizon formalism always gives rise to the same dual CFT pictures as the ones suggested by ASG of corresponding near horizon geometries. Furthermore, we propose new CFT duals for 4D Kerr-Newman-AdS-dS and higher dimensional Kerr-AdS-dS black holes. We find that every dual CFT is defined with respect to a rotation in certain angular direction, along which the translation defines a U(1) Killing symmetry. In the presence of two sets of U(1) symmetry, the novel CFT duals are generated by the modular group $SL(2,\mb Z)$, and for $n$ sets of U(1) symmetry there are general CFT duals generated by T-duality group $SL(n,\mb Z)$.

hep-th↗

arXiv2011

Spin-3 Topological Massive Gravity

In this paper, we study the spin-3 topological massive gravity(TMG), paying special attention to its properties at the chiral point. We propose an action describing the high spin fields coupled to TMG. We discuss the spin-3 fluctuations around the AdS$_3$ vacuum and find that there is an extra local massive mode, besides the left-moving and right-moving boundary massless modes. At the chiral point, such extra mode becomes massless and degenerates with the left-moving mode. We show that at the chiral point the only degrees of freedom in the theory are the boundary right-moving graviton and spin-3 field. We conjecture that spin-3 chiral gravity with Brown-Henneaux boundary condition is holographically dual to 2D chiral CFT with classical $W_3$ algebra and central charge $c_R=3l/G$.

hep-th↗

arXiv2011

Holographic Q-picture of Kerr-Newman-AdS-dS Black Hole

In this article, we show that a four-dimensional Kerr-Newman-AdS-dS black hole could be described by two different holographic two-dimensional conformal field theories. The first description, in view of the angular momentum, has been well discussed in (arXiv:1006.0157). The other alternative dual picture, however, is somehow overlooked. This new description, in view of the charge, provides another holographic correspondence. This picture again is supported not only by the match of the macroscopic entropy with the counting of microscopic degrees of freedom via the Cardy formula and also by the agreement on the real-time correlator in the superradiant scattering.

hep-th↗

arXiv2011

Discovery of Energy Dependent X-ray Microlensing in Q2237+0305

We present our long term Chandra X-ray monitoring data for the gravitationally lensed quasar Q2237+0305 with 20 epochs spanning 10 years. We easily detect microlensing variability between the images in the full (0.2--8 keV), soft (0.2--2 keV), and hard (2--8 keV) bands at very high confidence. We also detect, for the first time, chromatic microlensing differences between the soft and hard X-ray bands. The hard X-ray band is more strongly microlensed than the soft band, suggesting that the corona above the accretion disk thought to generate the X-rays has a non-uniform electron distribution, in which the hotter and more energetic electrons occupy more compact regions surrounding the black holes. Both the hard and soft X-ray bands are more strongly microlensed than the optical (restframe UV) emission, indicating that the X-ray emission is more compact than the optical, confirming the microlensing results from other lenses.

astro-ph.CO↗

arXiv2011

Holographic Correlation Functions for Open Strings and Branes

In this paper, we compute holographically the two-point and three-point functions of giant gravitons with open strings. We consider the maximal giant graviton in $S^5$ and the string configurations corresponding to the ground states of Z=0 and Y=0 open spin chain, and the spinning string in AdS$_5$ corresponding to the derivative type impurities in Y=0 or Z=0 open spin chain as well. We treat the D-brane and open string contribution separately and find the corresponding D3-brane and string configurations in bulk which connect the composite operators at the AdS$_5$ boundary. We apply a new prescription to treat the string state contribution and find agreements for the two-point functions. For the three-point functions of two giant gravitons with open strings and one certain half-BPS chiral primary operator, we find that the D-brane contributions to structure constant are always vanishing and the open string contribution for the Y=0 ground state is in perfect match with the prediction in the free field limit.

hep-th↗

arXiv2011

The Gravitational Lens Equation for Embedded Lenses; Magnification and Ellipticity

We give the lens equation for light deflections caused by point mass condensations in an otherwise spatially homogeneous and flat universe. We assume the signal from a distant source is deflected by a single condensation before it reaches the observer. We call this deflector an embedded lens because the deflecting mass is part of the mean density. The embedded lens equation differs from the conventional lens equation because the deflector mass is not simply an addition to the cosmic mean. We prescribe an iteration scheme to solve this new lens equation and use it to compare our results with standard linear lensing theory. We also compute analytic expressions for the lowest order corrections to image amplifications and distortions caused by incorporating the lensing mass into the mean.

astro-ph.CO↗

arXiv2011

Enhancement of the Superconducting Transition Temperature with Hydrostatic Pressure in Ca_{3}Ir_{4}Sn_{13} Single Crystals

We report high pressure magnetic susceptibility and electrical resistivity measurements on Ca_{3}Ir_{4}Sn_{13} single crystals up to 60 kbar. These measurements allow us to follow the evolution of the superconducting critical temperature T_c, the resistivity anomaly temperature T*, the superconducting coherence length and the Fermi velocity under pressure. The pressure-temperature phase diagram constructed for Ca_{3}Ir_{4}Sn_{13} shows a dome-shaped pressure dependence of T_c. The initial rise in T_c, which is accompanied by a decrease in T*, is consistent with a reduction in the partial gapping of the Fermi surface under pressure.

cond-mat.supr-con↗

arXiv2011

Boundary Conditions for NHEK through Effective Action Approach

We study the asymptotic symmetry group(ASG) of the near horizon geometry of extreme Kerr black hole through the effective action approach developed in 1007.1031. By requiring a finite boundary effective action, we derive a new set of asymptotic Killing vectors and boundary conditions, which are much more relaxed than the ones proposed in 0907.0303, and still allow a copy of conformal group as its ASG. In the covariant formalism, the asymptotic charges are finite, with the corresponding central charge vanishing. By using the quasi-local charge and introducing a plausible cut-off, we find that the higher order terms of the asymptotic Killing vectors, which could not be determined through the effective action approach, contribute to the central charge as well. We also show that the boundary conditions suggested in 0809.4266 lead to a divergent first order boundary effective action.

hep-th↗

arXiv2011

Spatially and Spectrally Resolved Observations of a Zebra Pattern in Solar Decimetric Radio Burst

We present the first interferometric observation of a zebra-pattern radio burst with simultaneous high spectral (~ 1 MHz) and high time (20 ms) resolution. The Frequency-Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe the X1.5 flare on 14 December 2006. By using OVSA to calibrate the FST the source position of the zebra pattern can be located on the solar disk. With the help of multi-wavelength observations and a nonlinear force-free field (NLFFF) extrapolation, the zebra source is explored in relation to the magnetic field configuration. New constraints are placed on the source size and position as a function of frequency and time. We conclude that the zebra burst is consistent with a double-plasma resonance (DPR) model in which the radio emission occurs in resonance layers where the upper hybrid frequency is harmonically related to the electron cyclotron frequency in a coronal magnetic loop.

astro-ph.SR↗

arXiv2011

Quasi-normal Modes of Extremal Black Holes from Hidden Conformal Symmetry

In this paper, we construct the quasi-normal modes of three-dimensional extremal black holes in an algebraic way. We show that the infinite towers of the quasi-normal modes of scalar, vector and tensor could be constructed as the descendents of the highest weight modes. Our investigation shows that the hidden conformal symmetry suggested in arXiv:1007.4269 is an intrinsic property of the extremal black hole. Moreover, we notice that we need to fix the freedom in defining the local vector fields and find the right hidden conformal symmetry to obtain the physical quasi-normal modes.

hep-th↗