2022 Vol. 46, No. 3
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The Large High Altitude Air Shower Observatory (LHAASO) (
In the γ-ray sky, the highest fluxes come from Galactic sources: supernova remnants (SNRs), pulsars and pulsar wind nebulae, star forming regions, binaries and micro-quasars, giant molecular clouds, Galactic center, and the large extended area around the Galactic plane. The radiation mechanisms of γ-ray emission and the physics of the emitting particles, such as the origin, acceleration, and propagation, are of very high astrophysical significance. A variety of theoretical models have been suggested for the relevant physics, and emission with energies E≥1014 eV are expected to be crucial in testing them. In particular, this energy band is a direct window to test at which maximum energy a particle can be accelerated in the Galactic sources and whether the most probable source candidates such as Galactic center and SNRs are “PeVatrons”. Designed aiming at the very high energy (VHE, >100 GeV) observation, LHAASO will be a very powerful instrument in these astrophysical studies. Over the past decade, great advances have been made in the VHE γ-ray astronomy. More than 170 VHE γ-ray sources have been observed, and among them, 42 Galactic sources fall in the LHAASO field-of-view. With a sensitivity of 10 milli-Crab, LHAASO can not only provide accurate spectra for the known γ-ray sources, but also search for new TeV-PeV γ-ray sources. In the following sub-sections, the observation of all the Galactic sources with LHAASO will be discussed in details.
Extra-galactic gamma-ray sources, such as gamma-ray bursts, active galactic nuclei, starburst galaxies, are interesting and important targets for LHAASO observations. In this chapter, the prospects of detecting these sources with LHAASO and their physical implications are studied. The upgrade plan for the Water Cherenkov Detector Array (WCDA), which aims to enhance the detectability of relatively lower energy photons, is also presented. In addition, a study on constraining the extragalactic background light with LHAASO observation of blazars is presented.
In the first part of this Chapter the present state of knowledge from the observations of cosmic rays between 1013 and 1020 eV is summarized. This is not intended to be a complete review, but rather a broad overview of the relevant processes involving cosmic rays, including the astrophysical environments in which they take place. This overview mainly concerns experimental results and phenomenological aspects of their interpretation, therefore experiments’ description is not given but references to the vast bibliography are provided in the text. Some attempt is made to address the most popular explanations offered by theoretical models. The second part is devoted to the description of the LHAASO performance and of its capability to provide a response to several open questions, still unanswered, concerning cosmic rays above 1013 eV, highlighting which major steps forward in this field could be taken from LHAASO observations.
In order to reveal the nature of dark matter, it is crucial to detect its non-gravitational interactions with the standard model particles. The traditional dark matter searches focused on the so-called weakly interacting massive particles. However, this paradigm is strongly constrained by the null results of current experiments with high precision. Therefore there is a renewed interest of searches for heavy dark matter particles above TeV scale. The Large High Altitude Air Shower Observatory (LHAASO) with large effective area and strong background rejection power is very suitable to investigate the gamma-ray signals induced by dark matter annihilation or decay above TeV scale. In this document, we review the theoretical motivations and background of heavy dark matter. We review the prospects of searching for the gamma-ray signals resulted from dark matter in the dwarf spheroidal satellites and Galactic halo for LHAASO, and present the projected sensitivities. We also review the prospects of searching for the axion-like particles, which are a kind of well motivated light pseudo-scalars, through the LHAASO measurement of the very high energy gamma-ray spectra of astrophysical sources.
Combining observations of multi-messengers help in boosting the sensitivity of astrophysical source searches, and probe various aspects of the source physics. In this chapter we discuss how LHAASO observations of very high energy (VHE) gamma rays in combination with telescopes for the other messengers can help in solving the origins of VHE neutrinos and galactic and extragalactic cosmic rays.
In the following sub-sections, studies of solar-heliospheric effects on cosmic rays, investigating a possible link between cosmic ray flux and Earth’s climate, and detection of MeV-range γ-rays from thunderstorms with the data from LHAASO will be discussed; geophysical research with environmental neutrons will be introduced, and some Monte Carlo simulation results about effects of thunderstorm electric fields on LHAASO observations of cosmic rays will be given.
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