The ARGO-YBJ experiment in Tibet

The ARCO-YBJ experiment, (Astrophysical Radiation Ground-based Observatory at YaugBaJing) is under construction in Tibet, 90 kill to the north of Lhasa. The full coverage approach and the high altitude location allow the study of many physics items in the field of low energy cosmic rays, namely gamma-ray astronomy, diffuse gamma-rays, gamma-ray bursts (GRBs), proton/antiproton ratio, primary proton spectrum and heliosphere physics, In this paper the expected sensitivities of ARGO-YBJ for gamma astronomy and GRB physics are presented and compared with the present experimental techniques and results. The performance of a test-module of similar to 50 m(2) operated on-site is, also discussed

The ARGO-YBJ experiment in Tibet

The ARCO-YBJ experiment, (Astrophysical Radiation Ground-based Observatory at YaugBaJing) is under construction in Tibet, 90 kill to the north of Lhasa. The full coverage approach and the high altitude location allow the study of many physics items in the field of low energy cosmic rays, namely gamma-ray astronomy, diffuse gamma-rays, gamma-ray bursts (GRBs), proton/antiproton ratio, primary proton spectrum and heliosphere physics, In this paper the expected sensitivities of ARGO-YBJ for gamma astronomy and GRB physics are presented and compared with the present experimental techniques and results. The performance of a test-module of similar to 50 m(2) operated on-site is, also discussed

LONG-TERM MONITORING OF THE TeV EMISSION FROM Mrk 421 WITH THE ARGO-YBJ EXPERIMENT

ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. It is operated with a high duty cycle and a large field of view. It continuously monitors the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from 2007 November to 2010 February. This source was observed by the satellite-borne experiments Rossi X-ray Timing Explorer and Swift in the X-ray band. Mrk 421 was especially active in the first half of 2008. Many flares are observed in both X-ray and gamma-ray bands simultaneously. The gamma-ray flux observed by ARGO-YBJ has a clear correlation with the X-ray flux. No lag between the X-ray and gamma-ray photons longer than 1 day is found. The evolution of the spectral energy distribution is investigated by measuring spectral indices at four different flux levels. Hardening of the spectra is observed in both X-ray and gamma-ray bands. The gamma-ray flux increases quadratically with the simultaneously measured X-ray flux. All these observational results strongly favor the synchrotron self-Compton process as the underlying radiative mechanism

Early warning for VHE gamma-ray flares with the ARGO-YBJ detector

Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, > 100 GeV) band is a very important topic in gamma-ray astronomy. The ARGO-YBJ detector is characterized by a high duty cycle and a wide field of view. Therefore, it is particularly capable of detecting flares from extragalactic objects. Based on fast reconstruction and analysis, real-time monitoring of 33 selected VHE extragalactic sources is implemented. Flares exceeding a specific threshold are reported timely, hence enabling the follow-up observation of these objects using more sensitive detectors, such as Cherenkov telescopes. (C) 2011 Elsevier B.V. All rights reserved

Early warning for VHE gamma-ray flares with the ARGO-YBJ detector

Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, > 100 GeV) band is a very important topic in gamma-ray astronomy. The ARGO-YBJ detector is characterized by a high duty cycle and a wide field of view. Therefore, it is particularly capable of detecting flares from extragalactic objects. Based on fast reconstruction and analysis, real-time monitoring of 33 selected VHE extragalactic sources is implemented. Flares exceeding a specific threshold are reported timely, hence enabling the follow-up observation of these objects using more sensitive detectors, such as Cherenkov telescopes. (C) 2011 Elsevier B.V. All rights reserved

Software timing calibration of the ARGO-YBJ detector

The ARGO-YBJ experiment is mainly devoted to search for astronomical gamma sources. The arrival direction of air showers is reconstructed thanks to the times measured by the pixels of the detector. Therefore, the timing calibration of the detector pixels is crucial in order to get the best angular resolution and pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore an off-line software calibration has been adopted. Here, the details of the procedure and the results are presented. (C) 2008 Elsevier B.V. All rights reserved

Layout and performance of RPCs used in the Argo-YBJ experiment

The layout of the RPCs, used in the Argo-YBJ experiment to image with a high space-time granularity the atmospheric shower, is described in this paper. The detector has been assembled to provide both digital and analog informations in order to cover a wide particle density range with a time accuracy of 1 ns. The experimental results obtained operating the chambers in streamer mode at sea level with a standard gas mixture are presented. (c) 2006 Elsevier B.V. All rights reserved

Light-component spectrum of the primary cosmic rays in the multi-TeV region measured by the ARGO-YBJ experiment

The ARGO-YBJ experiment detects extensive air showers in a wide energy range by means of a full-coverage detector which is in stable data taking in its full configuration since November 2007 at the YBJ International Cosmic Ray Observatory (4300 m a.s.l., Tibet, People's Republic of China). In this paper the measurement of the light-component spectrum of primary cosmic rays in the energy region (5 divided by 200) TeV is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment