120027918
SPIN EXPANSION FOR HEAD-ON COLLISION OF TWO BLACK HOLES
The spin expansion technique proposed in [L. Boyel, M. Kesden and S. Nissanke, Phys. Rev. Lett.100 (2008) 151101] is very powerful to analyze the relation between the initial state of binary black hole and the final state of the merged black hole. But this technique needs orbital angular momentum to determine the third direction of a triad. Without this triad we cannot get the decomposed components of the involved quantities, and the spin expansion breaks down. The head-on collision of two black holes, whose orbital angular momentum vanishes, falls into this case. In this paper we propose a new method to construct a triad for spin expansion technique. With this new method, we get the same set of equations as in the above-mentioned paper. Furthermore, we use numerical simulations to illustrate the validity of our new method for the head-on collision of two black holes.
8231444
Hawking Radiation from Spherically Symmetrical Gravitational Collapse to an Extremal R-N Black Hole for a Charged Scalar Field*
Si-Jie Gao has recently investigated Hawking radiation from spherically symmetrical gravitational collapse to an extremal R-N black hole for a real scalar field. Especially he estimated the upper bound for the expected number of particles in any wave packet belonging to H-out spontaneously produced from the state \0>(in), which confirms the traditional belief that extremal black holes do not radiate particles. Making some modifications, we demonstrate that the analysis can go through for a charged scalar field.
122996811
Newman-Penrose constants of the Kerr-Newman metric
The Newman-Unti formalism of the Kerr-Newman metric near future null infinity is developed, with which the Newman-Penrose constants for both the gravitational and electromagnetic fields of the Kerr-Newman metric are computed and shown to be zero. The multipole structure near future null infinity in the sense of Janis-Newman of the Kerr-Newman metric is then further studied. It is found that up to the ${2}^{4}$-pole, modulo a constant dependent upon the order of the pole, these multipole moments agree with those of Geroch-Hansen multipole moments defined at spatial infinity.
119264530
Numerical stability of the Z4c formulation of general relativity
We study numerical stability of different approaches to the discretization of a conformal decomposition of the Z4 formulation of general relativity. We demonstrate that in the linear, constant coefficient regime a novel discretization for tensors is formally numerically stable with a method of lines time-integrator. We then perform a full set of apples with apples tests on the non-linear system, and thus present numerical evidence that both the new and standard discretizations are, in some sense, numerically stable in the non-linear regime. The results of the Z4c numerical tests are compared with those of BSSNOK evolutions. We typically do not employ the Z4c constraint damping scheme and find that in the robust stability and gauge wave tests the Z4c evolutions result in lower constraint violation at the same resolution as the BSSNOK evolutions. In the gauge wave tests we find that the Z4c evolutions maintain the desired convergence factor over many more light-crossing times than the BSSNOK tests. The difference in the remaining tests is marginal.
119160554
THE ARGO-YBJ EXPERIMENT PROGRESSES AND FUTURE EXTENSION
Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray origins. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. To target the goals, the ARGO-YBJ experiment has been established. Significant progresses have been made in the experiment. A large air shower detector array in an area of 1 km2 is proposed to boost the sensitivity. Hybrid detections with multi-techniques will allow a good discrimination between different types of primary particles, including photons and protons, thus enable an energy spectrum measurement for individual species. Fluorescence light detector array will extend the spectrum measurement to 100 PeV and higher where the second knee is located. An energy scale determined by balloon experiments at 10 TeV will be propagated to ultra high energy cosmic ray experiments.
121086320
Cosmic Ray Experiments in the Era of LHC
Many uncertainties in cosmic ray experiments will be eliminated with more measurements about interaction between nucleons in the Large Hadron Collider (LHC) experiment. Cosmic ray experiments will enter an era marked by the high precision of measurements carried out by combining multipurpose instruments on very large scales. They have been putting strict constraints on models of cosmic ray acceleration at sources and propagation through the universe. Measurements of electrons, all kinds of nuclei, even gamma rays and neutrinos will enhance the opportunity of breakthrough in solving the mystery of origin of cosmic rays or even finding the source of the dark matter. A fundamental problem in cosmic ray experiments is the energy scale of ground based experiments for ultra high energy cosmic rays. A unique and straightforward approach is to match the energy spectra of nuclei measured by space or balloon borne experiments with what measured by ground based detectors at high altitudes and propagate the scale up ...
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.
32243559
The measurement of UHECR spectrum with the HiRes experiment in stereo mode
In this paper, the energy spectrum of UHECR with energy above 10 18.2 eV has been measured with HiRes detector in stereo mode. The cosmic ray events reconstruction has been presented briefly. A new direction reconstruction method has been introduced. The resolution of arrival direction is about 0.44 degree and the energy resolution is about 10%. The detector aperture is studied in detail, and an aerosol free aperture is given. At last, the result on the UHECR spectrum is presented and its uncertainty is discussed.
118444189
Multi-wavelength study of the MGRO J2019+37
MGRO J2019+37 within the Cygnus region is a bright and extended source revealed by Milagro at 12-35 TeV. This source is almost as bright as Crab Nebula in northern sky, while it is not confirmed by ARGO-YBJ around TeV. Up to now, no obvious counterpart at low energy wavelengths has been found. Hence, MGRO J2019+37 becomes mysterious and its VHE gamma-ray emission mechanism is attractive. In this paper, a brief summary of the multi-wavelength observations from Radio to gamma-ray is presented. All the available data from the XMM-Newton and INTEGRAL at X-ray, and the Fermi-LAT at gamma-ray bands were used to get constraint on its emission flux at low energy wavelengths. Then, its possible counterparts and the VHE emission mechanism are discussed.