10 research outputs found
Exploring Lorentz Invariance Violation from Ultra-high-energy Gamma Rays Observed by LHAASO
Recently the LHAASO Collaboration published the detection of 12 ultra-high-energy gamma-ray sources above 100 TeV, with the highest energy photon reaching 1.4 PeV. The first detection of PeV gamma rays from astrophysical sources may provide a very sensitive probe of the effect of the Lorentz invariance violation (LIV), which results in decay of high-energy gamma rays in the superluminal scenario and hence a sharp cutoff of the energy spectrum. Two highest energy sources are studied in this work. No signature of the existence of LIV is found in their energy spectra, and the lower limits on the LIV energy scale are derived. Our results show that the first-order LIV energy scale should be higher than about 10^5 times the Planck scale M_{pl} and that the second-order LIV scale is >10^{-3}M_{pl}. Both limits improve by at least one order of magnitude the previous results
Construction and On-site Performance of the LHAASO WFCTA Camera
The focal plane camera is the core component of the Wide Field-of-view
Cherenkov/fluorescence Telescope Array (WFCTA) of the Large High-Altitude Air
Shower Observatory (LHAASO). Because of the capability of working under
moonlight without aging, silicon photomultipliers (SiPM) have been proven to be
not only an alternative but also an improvement to conventional photomultiplier
tubes (PMT) in this application. Eighteen SiPM-based cameras with square light
funnels have been built for WFCTA. The telescopes have collected more than 100
million cosmic ray events and preliminary results indicate that these cameras
are capable of working under moonlight. The characteristics of the light
funnels and SiPMs pose challenges (e.g. dynamic range, dark count rate,
assembly techniques). In this paper, we present the design features,
manufacturing techniques and performances of these cameras. Finally, the test
facilities, the test methods and results of SiPMs in the cameras are reported
here.Comment: 45 pages, 21 figures, articl
Energy spectrum of cosmic protons and helium nuclei by a hybrid measurement at 4300 m a.s.l.
The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called
âkneeâ by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber
(RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been
well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy
resolution of about 25% is achieved throughout the whole energy range (100â700 TeV). The observed energy spectrum
is compatible with a single power law with index
Îł
=â2.63±0.0
Construction and on-site performance of the LHAASO WFCTA camera
The focal plane camera is the core component of the Wide Field-of-view Cherenkov/fluorescence Telescope Array (WFCTA) of the Large High-Altitude Air Shower Observatory (LHAASO). Because of the capability of working under moonlight without aging, silicon photomultipliers (SiPM) have been proven to be not only an alternative but also an improvement to conventional photomultiplier tubes (PMT) in this application. Eighteen SiPM-based cameras with square light funnels have been built for WFCTA. The telescopes have collected more than 100 million cosmic ray events and preliminary results indicate that these cameras are capable of working under moonlight. The characteristics of the light funnels and SiPMs pose challenges (e.g. dynamic range, dark count rate, assembly techniques). In this paper, we present the design features, manufacturing techniques and performances of these cameras. Finally, the test facilities, the test methods and results of SiPMs in the cameras are reported here
The First LHAASO Catalog of Gamma-Ray Sources
We present the first catalog of very-high-energy and ultra-high-energy gamma-ray sources detected by the Large High Altitude Air Shower Observatory. The catalog was compiled using 508 days of data collected by the Water Cherenkov Detector Array from 2021 March to 2022 September and 933 days of data recorded by the Kilometer Squared Array from 2020 January to 2022 September. This catalog represents the main result from the most sensitive large coverage gamma-ray survey of the sky above 1 TeV, covering decl. from â20° to 80°. In total, the catalog contains 90 sources with an extended size smaller than 2° and a significance of detection at >5 Ï . Based on our source association criteria, 32 new TeV sources are proposed in this study. Among the 90 sources, 43 sources are detected with ultra-high energy ( E > 100 TeV) emission at >4 Ï significance level. We provide the position, extension, and spectral characteristics of all the sources in this catalog
Active galactic nuclei: whatâs in a name?
Active Galactic Nuclei (AGN) are energetic astrophysical sources powered by
accretion onto supermassive black holes in galaxies, and present unique
observational signatures that cover the full electromagnetic spectrum over more
than twenty orders of magnitude in frequency. The rich phenomenology of AGN has
resulted in a large number of different "flavours" in the literature that now
comprise a complex and confusing AGN "zoo". It is increasingly clear that these
classifications are only partially related to intrinsic differences between
AGN, and primarily reflect variations in a relatively small number of
astrophysical parameters as well the method by which each class of AGN is
selected. Taken together, observations in different electromagnetic bands as
well as variations over time provide complementary windows on the physics of
different sub-structures in the AGN. In this review, we present an overview of
AGN multi-wavelength properties with the aim of painting their "big picture"
through observations in each electromagnetic band from radio to gamma-rays as
well as AGN variability. We address what we can learn from each observational
method, the impact of selection effects, the physics behind the emission at
each wavelength, and the potential for future studies. To conclude we use these
observations to piece together the basic architecture of AGN, discuss our
current understanding of unification models, and highlight some open questions
that present opportunities for future observational and theoretical progress.Comment: Accepted for publication in Astronomy & Astrophysics Review, 56
pages, 25 figure