117323209
Search for GRB counterparts using the ARGO‐YBJ experiment in shower mode
In this paper, the effective area of the ARGO‐YBJ experiment to detect the gamma rays with energy range from 10 GeV to 1 TeV for different incident zenith angles (0,10,20,30,40 degrees) is given respectively. The optimal event selections to search for GRB counterparts with different cutoff energy models (Ecut = 100 GeV and 1 TeV) are studied. Using these selections and their corresponding angular resolutions the searches are done within two hours around the GRB trigger time via different time windows. Finally, the result for the 20 GRBs in the field of view of ARGO between July 2006 and July 2008 is presented, and the fluence upper limit for each GRB is set at 99% confidence level.
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.
55209539
Characteristic Plane Method with Conical Correction
In ground-based cosmic ray experiments, the equalization of the transit time of signals coming from different parts of the apparatus is of crucial importance for the improvement of the angular resolution and accuracy. In the ARGO-YBJ experiment, this is achieved using the Characteristic Plane Method with conical correction, studied by both Monte Carlo simulation and real data and also checked with manual absolute calibration on a portion of the detector. By introducing conical correction in primary direction reconstruction, the systematics error existing in the off-line calibration with planar fit is successfully removed. Two subsequent construction phases of the detector have been considered: ARGO-42 and ARGO-104. During the calibration of ARGO-104, events with more than 1000 hits and with the core reconstructed inside the carpet were used in order to achieve a good reconstruction of the shower, that is the arrival direction and the core position. The results of the calibration concerning the two configurations, ARGO-42 and ARGO-104, are compared and discussed.
115310371
Preliminary results of the Moon shadow with ARGO-YBJ
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.
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.
118654249
Particle acceleration on the background of the Kerr―Taub―NUT spacetime
Abstract We study the collision of two particles with the different rest masses moving in the equatorial plane of a Kerr–Taub–NUT spacetime and get the center-of-mass (CM) energy for the particles. We find that the CM energy depends not only on the rotation parameter, a , but also on the NUT charge of the Kerr–Taub–NUT spacetime, n . Especially, for the extremal Kerr–Taub–NUT spacetime, an unlimited CM energy can be approached if the parameter a is in the range [ 1 , 2 ] , which is different from that of the Kerr and Kerr–Newman black holes.
118839273
Cosmological perturbations in f(T) gravity
We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbein, we extract the corresponding dispersion relation, which provides a constraint on the f(T) Ansaetze that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from {Lambda}CDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.
118628016
Is the CMB asymmetry due to the kinematic dipole
Parity violation found in the Cosmic Microwave Background (CMB) radiation is a crucial clue for the non-standard cosmological model or the possible contamination of various foreground residuals and/or calibration of the CMB data sets. In this paper, we study the directional properties of the CMB parity asymmetry by excluding the $m=0$ modes in the definition of parity parameters. We find that the preferred directions of the parity parameters coincide with the CMB kinematic dipole, which implies that the CMB parity asymmetry may be connected with the possible contamination of the residual dipole component. We also find that such tendency is not only localized at $l=2,3$, but in the extended multipole ranges up to $l\sim 22$.
119095217
Properties of a thin accretion disk around a rotating non-Kerr black hole
Abstract We study the accretion process in the thin disk around a rotating non-Kerr black hole with a deformed parameter and an unbound rotation parameter. Our results show that the presence of the deformed parameter ϵ modifies the standard properties of the disk. For the case in which the black hole is more oblate than a Kerr black hole, the larger deviation leads to the smaller energy flux, the lower radiation temperature and the fainter spectra luminosity in the disk. For the black hole with positive deformed parameter, we find that the effect of the deformed parameter on the disk becomes more complicated. It depends not only on the rotation direction of the black hole and the orbit particles, but also on the sign of the difference between the deformed parameter ϵ and a certain critical value ϵ c . These significant features in the mass accretion process may provide a possibility to test the no-hair theorem in the strong-field regime in future astronomical observations.
195822336
CURRENT STATUS OF THE PROPOSED SHANGHAI SYNCHROTRON RADIATION FACILITY
The Shanghai Synchrotron Radiation Facility (SSRF) was proposed by the Chinese Academy of Sciences and the Shanghai Municipal Government in 1995. The estimated total budget is around US$100 M, and the operation is scheduled to begin in the end of 2003. The whole SSRF project is still awaiting final approval, but its R&D has been approved. The SSRF is a third-generation synchrotron light source designed to produce high brightness VUV and soft X-ray in the energy region of 10 eV~3 keV and high flux X-ray with moderate brightness in the energy region of 3~30 keV. It consists of the injector (including a 100 MeV Linac and a 2.2-2.5 GeV Booster), the 2.2-2.5 GeV storage ring and the synchrotron radiation experimental facilities. In this paper, the main parameters and features of the SSRF are presented.