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Register a new userThe Gamma Ray Detection sensitivity of the upgraded VERITAS Observatory
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Authors
D. B. Kieda
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The VERITAS VHE gamma-ray observatory recently completed a major upgrade of its camera and pattern triggering systems. Bias curve testing of the upgraded VERITAS Observatory under dark sky conditions indicates a 50% increase in photon detection efficiency, and a 30% reduction in triggering threshold. Optimization of analysis of the Crab nebula observations performed in late 2012 and early 2013 is ongoing. A comparison of these results with pre-upgrade Crab observations can provide the most direct method for quantifying the impact of the upgrade on VERITAS sensitivity and energy threshold.
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The HAWC collaboration has recently completed the construction of a gamma-ray observatory at an altitude of 4100 meters on the slope of the Sierra Negra volcano in the state of Puebla, Mexico. In order to achieve an optimal angular resolution, energy reconstruction, and cosmic-ray background suppression for the air showers observed by HAWC, it is crucial to obtain good timing and charge calibrations of the photosensors in the detector. The HAWC calibration is based on a laser system which is able to deliver short light pulses to all the tanks in the array. The light intensity can range over 7 orders of magnitude, broad enough to cover all the dynamic range of the PMT readout electronics. In this contribution we will present the HAWC calibration system, together with the methods used to calibrate the detector.
The scientific potential of a wide field-of-view, and very-high duty cycle, ground-based gamma-ray detector has been demonstrated by the current generation of instruments, such as HAWC and ARGO, and will be further extended in the Northern Hemisphere by LHAASO. Nevertheless, no such instrument exists in the Southern Hemisphere yet, where a great potential lies uncovered for the mapping of Galactic large scale emission as well as providing access to the full sky for transient and variable multi-wavelength and multi-messenger phenomena. Access to the Galactic Centre and complementarity with the CTA-South are other key motivations for such a gamma-ray observatory in the South. There is also significant potential for cosmic ray studies, including investigation of cosmic-ray anisotropy. In this contribution I will present the motivations and the concept of the future Southern Wide-Field Gamma-ray Observatory (SWGO), now formally established as an international Collaboration and currently in R&D phase. I will also outline its scientific objectives.
The High-Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is under construction 4100 meters above sea level at Sierra Negra, Mexico. We describe the design and cabling of the detector, the characterization of the photomultipliers, and the timing calibration system. We also outline a next-generation detector based on the water Cherenkov technique.
It has been established that Gamma-Ray Bursts (GRB) can produce Very High Energy radiation (E > 100 GeV), opening a new window on the investigation of particle acceleration and radiation properties in the most energetic domain. We expect that next-generation instruments, such as the Cherenkov Telescope Array (CTA), will mark a huge improvement in their observation. However, constraints on the target visibility and the limited duty cycle of Imaging Atmospheric Cherenkov Telescopes (IACT) reduce their ability to react promptly to transient events and to characterise their general properties. Here we show that an instrument based on the Extensive Air Shower (EAS) array concept, proposed by the Southern Wide Field-of-view Gamma-ray Observatory (SWGO) Collaboration, has promising possibilities to detect and track VHE emission from GRBs. Observations made by the Fermi Large Area Telescope (Fermi-LAT) identified some events with a distinct spectral component, extending above $1,$GeV or even $10,$GeV, which can represent a substantial fraction of the emitted energy and also arise in early stages of the process. Using models based on these properties, we estimate the possibilities that a wide field of view and large effective area ground-based monitoring facility has to probe VHE emission from GRBs. We show that the ability to monitor VHE transients with a nearly continuous scanning of the sky grants an opportunity to access simultaneous electromagnetic counterparts to Multi-Messenger triggers up to cosmological scales, in a way that is not available to IACTs.
The motivation, physics objectives, and technical strategy of a upgrade to the Pierre Auger Observatory are discussed.
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