The Review of [formula omitted]-ray Astronomical Observing Techniques

Introduction to Large High Altitude Air Shower Observatory (LHAASO)

The evolution of extensive air shower detection as a technique for γ-ray astronomical instrumentation for the last three decades is reviewed. The first discoveries of galactic PeVatrons by the Large High Altitude Air Shower Observatory demonstrate the importance of this technique in ultra-high energy γ-ray astronomy. Utilizing this technique, the origins of high energy cosmic rays may be discovered in the near future.

A Large Array of imaging atmospheric Cherenkov Telescopes (LACT) will be constructed at the Large High Altitude Air Shower Observatory site to explore the nature of PeV gamma-ray sources. The cameras of LACT will use Silicon Photomultipliers (SiPMs) as the photodetector. A dedicated test system was built to select SiPMs for LACT. The characteristics of six SiPM models from three manufacturers (Hamamatsu, Joinbon, and ON Semiconductor) were evaluated. Based on the characteristics of the candidate SiPMs and their preamplifiers, a Wiener-deconvolution algorithm is implemented to correct the pileup of the SiPM output pulses. The measurement methods and results for breakdown voltage, gain, dark count rate, optical crosstalk, and afterpulsing of the candidate SiPMs are reported in this article.

The origin of sub-TeV gamma rays detected by the \textit{Fermi}-Large Area Telescope (LAT) from the \textit{Fermi} Bubbles (FBs) at the Galactic center is still uncertain. In a hadronic model, acceleration of protons and/or nuclei and their subsequent interactions with gas in the bubble volume can produce the observed gamma rays. Recently the High Altitude Water Cherenkov (HAWC) observatory reported an absence of gamma-ray excess from the Northern FB at $b\gtrsim 6^\circ$ Galactic latitude, which resulted in flux upper limits in the energy range of $1.2-126$ TeV. These upper limits are consistent with the gamma-ray spectrum measured by \textit{Fermi}-LAT at $|b|\ge 10^\circ$, where an exponential cutoff at energies $\gtrsim 100$ GeV is evident. However, the FB gamma-ray spectrum at $|b|\le 10^\circ$, without showing any sign of cutoff up to around 1 TeV in the latest results, remains unconstrained. The upcoming Cherenkov Telescope Array (CTA) will perform a Galactic center survey with unprecedented sensitivity in the energy between 20 GeV and 300 TeV. In this work, we perform both morphological and classic on/off analyses with planned CTA deep central and extended survey and estimate the sensitivity of CTA to the FB hadronic gamma-ray flux models that best fit the spectrum at $|b|\le 10^\circ$ and whose counterpart neutrino flux model best fits the optimistic neutrino spectrum from IceCube Neutrino Observatory. We also perform sensitivity analysis with a future ground-based Cherenkov detector the Large High Altitude Air Shower Observatory (LHAASO). We find that CTA will be able to discover or constrain the FB gamma-ray flux at $|b|\le 10^\circ$ in the $\approx$ 200 GeV -- 100 TeV range with planned observation strategy, while LHAASO may constrain emission in the $\approx 100$~GeV -- 100~TeV range if $\lesssim 10\%$ systematic uncertainties can be achieved.

Status of the large high altitude air shower observatory project

The Sun albedo of Cosmic Rays (CRs) at GeVs energy has been discovered recently by the FERMI satellite. They are traces of atmospheric CRs hitting solar atmosphere and reflecting skimming gamma photons. Even if relevant for astrophysics, as being a trace of atmospheric solar CR noises they cannot offer any signal of neutrino astronomy. On the contrary, the Moon with no atmosphere, may become soon a novel filtering calorimeter and an amplifier of energetic muon astronomical neutrinos (at TeV up to hundred TeVs energy); these lepton tracks leave an imprint in their beta decay while in flight to Earth. Their TeV electron air-shower are among the main signals. Also, a more energetic, but more rare, PeV up to EeV tau lunar neutrino events may be escaping as a tau lepton from the Moon: [Formula: see text] PeV secondaries, then, may be shining on Earth’s atmosphere in lunar shadows in a surprising way. One or a few gamma air-shower events inside the Moon shadows may occur each year in near future Cherenkov telescope array (CTA) or large high altitude air shower observatory (LHAASO) TeV gamma array detector, assuming a nonnegligible astrophysical TeV up to hundred TeV neutrino component (with respect to our terrestrial ruling atmospheric ones); these signals will open a new wonderful passe-partout keyhole for neutrino, been seen along the Moon. The lunar solid angle is small and the muon or tau expected rate is rare, but with the future largest tau radio array as the giant radio array for neutrino detection (GRAND), one might well discover such neutrino imprint.

The detection of very high-energy neutrinos by IceCube experiment supports the existence of a comparable gamma-ray counterpart from the same cosmic accelerators. Under the likely assumption that the sources of these particles are of extragalactic origin, the emitted photon flux would be significantly absorbed during its propagation over cosmic distances. However, in the presence of photon mixing with ultra-light axion-like-particles (ALPs), this expectation would be strongly modified. Notably, photon-ALP conversions in the host galaxy would produce an ALP flux which propagates unimpeded in the extragalactic space. Then, the back-conversion of ALPs in the Galactic magnetic field leads to a diffuse high-energy photon flux. In this context, the recent detection of the diffuse high-energy photon flux by the Large High Altitude Air Shower Observatory (LHAASO) allows us to exclude at the 95% CL an ALP-photon coupling g_{agamma } > rsim 3.9–7.8 times 10^{-11}~mathrm {GeV^{-1}} for m_{a}lesssim 4times 10^{-7}~textrm{eV}, depending on the assumptions on the magnetic fields and on the original gamma-ray spectrum. This new bound is complementary with other ALP constraints from very-high-energy gamma-ray experiments and sensitivities of future experiments.

The Large High Altitude Air Shower Observatory (LHAASO) is a hybrid extensive air shower (EAS) array with an area of about 1 𝑘𝑚2 at an altitude of 4410 m a.s.l. in Sichuan province, China. It contains three sub-detectors: 1 𝑘𝑚2 array (KM2A) composed of 5195 electromagnetic particle detectors (ED) and muon detectors (MD); water Cerenkov detector array (WCDA) and 18 Wide Field-of-view Cerenkov Telescope Array (WFCTA). One of the main scientific goals is measuring the individual energy spectra of cosmic rays from ~30 TeV to a couple of EeV. The construction of the whole observatory will be completed by the end of 2021. In this paper, a new energy reconstruction method and result based on KM2A simulated nuclei events will be shown.

The intensity of Galactic cosmic rays in the arrival directions is highly isotropic; however, many cosmic ray experiments have observed weak anisotropies of various angular sizes. In this work, we report the observation of the medium-scale structures with the square kilometer array of the Large High Altitude Air Shower Observatory(LHAASO-KM2A). We have found that the positions of the excess regions, located at $\alpha \sim 315^{\circ}$, $\delta \sim 21^{\circ}$ (around 17 TeV), and $\alpha \sim 125$, $\delta \sim 42^{\circ}$, provide compelling evidence of energy dependence within the energy range of 10 TeV to over 100 TeV. Furthermore, the evolution behaviors of energy dependence may indicate that local complex turbulent environments play a potential role in the propagation of cosmic rays, which offers a new perspective on their origin and transport of cosmic rays.

The Cherenkov Telescope Array (CTA) observatory will probe the non-thermal universe above 20 GeV up to several hundreds of TeV with a significant improvement in sensitivity and angular resolution compared to current experiments. Its outstanding capabilities will allow to increase the number of extragalactic cosmic accelerators detected at very high energy (VHE) and therefore to better constrain the population of VHE accelerators and the gamma-ray absorption processes in the intergalactic medium. For the first time in the history of imaging atmospheric Cherenkov telescopes (IACTs), CTA will be an open observatory and high-level data will be made available to the astronomical community. Gammapy is an open-source Python package developed by the Cherenkov telescope community that provides tools to simulate the gamma-ray sky and analyse IACT data. The versatile architecture of, and steady user contributions to Gammapy enable a large variety of high-level data analyses. Examples of Gaammapy applications are presented, particularly in the context of extragalactic science with CTA.

The Large High Altitude Air Shower Observatory (LHAASO) 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 the energy spectrum and composition of cosmic rays by measuring the total Cherenkov light generated by air showers and the shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial for 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 the 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.

The aim of the Large High Altitude Air Shower Observatory (LHAASO), supported by IHEP of the Chinese Academy of Sciences, is a multipurpose project with a complex detectors array for high energy gamma ray and cosmic ray detection. The Wide Field of view Cherenkov Telescope Array (WFCTA), as one of the components of the LHAASO project, aim to tag each primary particle that causes an air shower. The WFCTA is a portable telescope array used to detect cosmic ray spectra. The design of the readout electronics of the WFCTA is described in this paper Sixteen photomultiplier tubes (PMTs), together with their readout electronics are integrated into a single sub-cluster. To maintain good resolution and linearity over a wide dynamic range, a dual-gain amplification configuration on an analog board is used The digital board contains two 16channel 14-bit, 50 Msps analog-to-digital converters (ADC) and its power consumption, noise level, and relative deviation are all tested.

The Large High Altitude Air Shower Observatory (LHAASO) is located in Haizi Mountain, Daocheng County, Sichuan Province, with an average altitude of 4410 m. The Wide Field of view Cherenkov Telescope Array (WFCTA) is one of its three observation arrays. Laser calibration system for WFCTA consists of 2 nitrogen lasers and 1 Nd:YAG laser system. During the operation of WFCTA, the outdoor temperature may dropped from 17 °C to about -30 °C, which will bring serious challenges to the operation of laser calibration system operating in the field. In order to ensure the stable working environment and remote operation of the laser, we have developed the LHAASO-WFCTA laser temperature control, remote control and data monitoring system. The fluctuation of temperature in the box is within 1 °C around the target. The laser temperature control system was officially put into operation in Sept. 2020. In this paper, the design scheme, fabrication scheme, comparison of heat dissipation coefficient and test of temperature control system are introduced. The working data shows that both nitrogen molecule lasers and Nd:YAG laser temperature control system can achieve stable and long-term operation in high-altitude extreme field.

Status of LHAASO updates from ARGO-YBJ

Ground Level Enhancement (GLE) events of solar cosmic ray refer to the sudden,sharp and short-lived enhancement of ground level energetic particles generated from solar flare. The study of GLE events has been playing an important role in the study of solar activity and basic physics of cosmic rays. The Large High Altitude Air Shower Observatory (LHAASO), a multi-component instrument, is located at high altitude (4410 m a.s.l.) in Daocheng, Sichuan province, P.R. China, with the one of the main aims to observe GLE events. The sensitivity of LHAASO WCDA to observe GLE events has been estimated in this paper. The minimum flux needed for LHAASO-WCDA to observe GLE event has been calculated by using the energy spectrum of 13 GLE events during 22 solar cycles. The result shows that LHAASO-WCDA can observe GLE events with the energy exceeds 50, 100, 500 or 1000 GeV.