119179510
Properties and performance of two wide field of view Cherenkov/fluorescence telescope array prototypes
A wide field of view Cherenkov/fluorescence telescope array is one of the main components of the Large High Altitude Air Shower Observatory project. To serve as Cherenkov and fluorescence detectors, a flexible and mobile design is adopted for easy reconfiguring of the telescope array. Two prototype telescopes have been constructed and successfully run at the site of the ARGO-YBJ experiment in Tibet. The features and performance of the telescopes are presented. (C) 2010 Elsevier B.V. All rights reserved.
118376307
Search for GeV Gamma‐Ray Bursts with the ARGO‐YBJ Detector in Scaler Mode
The ARGO‐YBJ experiment is a full coverage array made of Resistive Plate Chambers (RPCs) operated in streamer mode to detect the extensive array showers (EASs). With large field of view (>2sr) and high duty cycle (>90%), the ARGO‐YBJ detector is the right ground‐based apparatus to detect VHE GRBs, while the high altitude (4300 m a.s.l) and scaler working mode enable it to detect GRBs in the GeV region as high energy follow‐up observation of satellites such as SWIFT. If a GRB signal is detected, the four scaler channels, which correspond to different energy thresholds, can provide further information on the energy spectrum and its cut‐off. More than 40 SWIFT GRBs were in ARGO‐YBJ field of view, no significant excess was detected till now.
118578178
Observations of very high energy gamma-ray emission from AGNs with the ground-based EAS arrays
The ground-based EAS array is usually operated with a high duty cycle (> 90%) and a large field of view (∼ 2sr), which can continuously monitor the sky. It is essential and irreplaceable to understand the gamma-ray emission mechanism and intrinsic physics progress of the variable source AGN. The EAS arrays, AS-γ experiment (since 1990) and ARGO-YBJ experiment (since 2007), have continuously monitored the northern sky at energies above 3 TeV and 0.3 TeV, respectively. They have made substantial contributions for long-term monitoring of Mrk 421 and Mrk 501. In this paper, we will review the results obtained by the EAS arrays. The next generation of EAS array, LHAASO project, will boost the sensitivity of current EAS array at least up to 30 times with a much wider energy range from 40 GeV to 1 PeV. Beside increasing the number of VHE gamma-ray sources, it will guide us look sight into the properties of jet, and throw light on the determining of the EBL, intergalactic magnetic fields, and the validity of the Lorentz Invariance.
118403311
Geometry and optics calibration of WFCTA prototype telescopes using star light
The Large High Altitude Air Shower Observatory project is proposed to study high energy gamma ray astronomy ( 40 GeV-1 PeV ) and cosmic ray physics ( 20 TeV-1 EeV ). The wide field of view Cherenkov telescope array, as a component of the LHAASO project, will be used to study energy spectrum and compositions of cosmic ray by measuring the total Cherenkov light generated by air showers and shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial to the direction reconstruction of the primary particles. On the other hand the primary energy reconstruction relies on the shape of the Cherenkov image on the camera and the unrecorded photons due to the imperfect connections between photomultiplier tubes. UV bright stars are used as point-like objects to calibrate the pointing and to study the optical properties of the camera, the spot size and the fractions of unrecorded photons in the insensitive areas of the camera.
115310371
Preliminary results of the Moon shadow with ARGO-YBJ
118413139
TeV gamma-ray survey of the northern sky using the ARGO-YBJ experiment
The ARGO-YBJ experiment is an extensive air shower array that monitored the northern g-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper we present the result of a sky survey in the declination band from -10 ◦ to 70 ◦ , using the data recorded in more than five years. With a cumulative sensitivity ranging from 0.24 to ∼1 Crab units, depending on the declination, six sources have been observed with a statistical significance greater than 5 standard deviations. Several interesting hotspots are also reported as potential g-ray emitters. The features of each source are presented and discussed. Additionally, 95% confidence level upper limits to the flux from all sky regions are presented, which are more stringent than any previously published limits for TeV g-ray all-sky surveys. The specific upper limits for 663 GeV g-ray AGNs inside the ARGO-YBJ field of view are presented. The effect of the absorbtion of g-rays due to the interaction with the extragalactic background light are estimated.
119215629
Strong gravitational lensing in a squashed Kaluza-Klein Gödel black hole
We investigate the strong gravitational lensing in a squashed Kaluza-Klein black hole immersed in the G\"{o}del universe with global rotation. Our result show that the strong gravitational lensing in the squashed Kaluza-Klein G\"{o}del black hole spacetime has some distinct behaviors from that in the Kerr case. In the squashed Kaluza-Klein G\"{o}del black hole spacetime, the photon sphere radius, the minimum impact parameter, the coefficient $\bar{a}$, $\bar{b}$ and the deflection angle $\alpha(\theta)$ in the $\phi$ direction are independent of whether the photon goes with or against the global rotation of the G\"{o}del Universe. While in the Kerr black hole, the values of these quantities for the prograde photons are different from those for the retrograde photons. Moreover, the coefficient of $\bar{b}$ increases with $j$ in the squashed Kaluza-Klein G\"{o}del black hole, but decreases with $a$ in the Kerr case. We also probe the influence of the squashed effect on the strong gravitational lensing in this black hole and find that in the extremely squashed case $\rho_0=0$, the coefficient $\bar{a}$ is a constant 1 and is independent of the global rotation of the G\"{o}del Universe. Furthermore, we assume that the gravitational field of the supermassive central object of the Galaxy can be described by this metric and estimate the numerical values of the coefficients and the main observables in the strong gravitational lensing.
110035692
DESIGN OF LOW IMPEDANCE ELECTROSTATIC SEPARATORS FOR BEPC II
The multi bunch train collision is adopted in BEPC II. There are 4 horizontal electrostatic separators in the main ring to generate close-orbit displacement as "pretzels" which allow the electrons and positrons to be stored in the same vacuum chamber simultaneously without unwanted destructive collisions. In the separator the beam current (576mA) and the gap voltage (220 kV) are both very high. So there are five key problems that must be handled well: To reduce the beam impedance and loss factor; To absorb the high order modes (HOMs); To reduce the leakage of RF EM field; To extract the heats due to the HOMs losses and the SR power; To reduce the spark rate. Their analysis and the solutions are presented in this paper.
119228301
The big bang and inflation united by an analytic solution
Exact analytic solutions for a class of scalar-tensor gravity theories with a hyperbolic scalar potential are presented. Using an exact solution we have successfully constructed a model of inflation that produces the spectral index, the running of the spectral index, and the amplitude of scalar perturbations within the constraints given by the WMAP 7 years data. The model simultaneously describes the big bang and inflation connected by a specific time delay between them so that these two events are regarded as dependent on each other. In solving the Friedmann equations, we have utilized an essential Weyl symmetry of our theory in 3+1 dimensions which is a predicted remaining symmetry of 2T-physics field theory in 4+2 dimensions. This led to a new method of obtaining analytic solutions in the 1T field theory which could in principle be used to solve more complicated theories with more scalar fields. Some additional distinguishing properties of the solution includes the fact that there are early periods of time when the slow-roll approximation is not valid. Furthermore, the inflaton does not decrease monotonically with time; rather, it oscillates around the potential minimum while settling down, unlike the slow-roll approximation. While the model we used for illustrationmore » purposes is realistic in most respects, it lacks a mechanism for stopping inflation. The technique of obtaining analytic solutions opens a new window for studying inflation, and other applications, more precisely than using approximations.« less
119127372
Rotating charged black hole with Weyl corrections
We present firstly a four-dimensional spherical symmetric black hole with small Weyl corrections and find that with increasing Weyl corrections the region of the event horizon existence for the black hole in the parameter space increases for the negative Weyl coupling parameter and decreases for the positive one. Moreover, we also obtain a rotating charged black hole with weak Weyl corrections by the method of complex coordinate transformation. Our results show that the sign of Weyl coupling parameter $\alpha$ yields the different spatial topology of the event horizons for the black hole with its parameters lied in some special regions in the parameter space. We also analyze the dependence of the ergosphere on the Weyl coupling parameter $\alpha$ and find that with the increase of the Weyl corrections the ergosphere in the equatorial plane becomes thick for a black hole with $\alpha>0$, but becomes thin in the case with $\alpha<0$, which means that the energy extraction become easier in the background of a black hole with the positive Weyl coupling parameter, but more difficult in the background of a black hole with the negative one.
37077901
Asymptotic quasinormal modes of a coupled scalar field in the Gibbons-Maeda dilaton spacetime
Adopting the monodromy technique devised by Motl and Neitzke, we investigate analytically the asymptotic quasinormal frequencies of a coupled scalar field in the Gibbons–Maeda dilaton spacetime. We find that it is described by , which depends on the structure parameters of the background spacetime and on the coupling between the scalar and gravitational fields. As the parameters ξ and βI tend to zero, the real parts of the asymptotic quasinormal frequencies become THln 3, which is consistent with Hod's conjecture. When , the formula becomes that of the Reissner–Nordstrom spacetime.