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.
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.
14464884
Detector time offset and off-line calibration in EAS experiments
In extensive air shower (EAS) experiments, the primary direction is reconstructed by the space–time pattern of secondary particles. Thus the equalization of the transit time of signals coming from different parts of the detector is crucial in order to get the best angular resolution and pointing accuracy allowed by the detector. In this paper an off-line calibration method is proposed and studied by means of proper simulations. It allows to calibrate the array repeatedly just using the collected data without disturbing the standard acquisition. The calibration method is based on the definition of a Characteristic Plane introduced to analyze the effects of the time systematic offsets, such as the quasi-sinusoidal modulation on azimuth angle distribution. This calibration procedure works also when a pre-modulation on the primary azimuthal distribution is present.
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.
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.
115310371
Preliminary results of the Moon shadow with ARGO-YBJ
195862506
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 120M USD, and the operation is scheduled to begin by the end of 2004. Although the whole SSRF project is still awaiting final approval, its R&D has been approved already. The SSRF is a third generation light source designed to produce high brightness and flux soft X-ray and hard X-ray in the energy region of 0.1/spl sim/40 keV. It consists of a 300 MeV linac, a 3.5 GeV booster, a 3.5 GeV storage ring and dozens of beam lines and experimental stations. In this paper, the main parameters and features of the SSRF are presented.
118389950
Dark energy model with higher derivative of Hubble parameter
Abstract In this Letter we consider a dark energy model in which the energy density is a function of the Hubble parameter H and its derivative with respect to time ρ d e = 3 α H ¨ H − 1 + 3 β H ˙ + 3 γ H 2 . The behavior of the dark energy and the expansion history of the Universe depend heavily on the parameters of the model α , β and γ . It is very interesting that the age problem of the well-known three old objects can be alleviated in this models.
17776491
Noncommutativity as a possible origin of the ultrahigh energy cosmic ray and the TeV-photon paradoxes
In this paper, we present a general modified dispersion relation derived from q-deformed noncommutative theory and apply it to the ultrahigh energy cosmic ray and the TeV-photon paradoxes — threshold anomalies. Our purpose is not only trying to solve these puzzles by noncommutative theory but also to support noncommutative theory through the coincidence of the region in the parameter space for resolving the threshold anomalies with the one from the q-deformed noncommutative theory.
118374075
A new approach to the vacuum of inflationary models
A new approach is given for the implementation of boundary conditions used in solving the Mukhanov–Sasaki equation in the context of inflation. The familiar quantization procedure is reviewed, along with a discussion of where one might expect deviations from the standard approach to arise. The proposed method introduces a (model-dependent) fitting function for the z″/z and a″/a terms in the Mukhanov–Sasaki equation for scalar and tensor modes, as well as imposes the boundary conditions at a finite conformal time. As an example, we employ a fitting function and compute the spectral index, along with its running, for a specific inflationary model, which possesses background equations that are analytically solvable. The observational upper bound on the tensor to scalar ratio is used to constrain the parameters of the boundary conditions in the tensor sector as well. An overview on the generalization of this method is also discussed.
118507719
Greybody factor for a scalar field coupling to Einstein's tensor
Abstract We study the greybody factor and Hawking radiation for a scalar field coupling to Einstein's tensor in the background of Reissner–Nordstrom black hole in the low-energy approximation. We find that the presence of the coupling terms modifies the standard results in the greybody factor and Hawking radiation. Our results show that both the absorption probability and Hawking radiation increase with the coupling constant. Moreover, we also find that for the stronger coupling, the charge of black hole enhances the absorption probability and Hawking radiation of the scalar field, which is different from those of ones without coupling to Einstein's tensor in the black hole spacetime.