Large High Altitude Air Shower Observatory Research Articles

Self-calibration of LHAASO-KM2A electromagnetic particle detectors using single particles within extensive air showers

In the Large High Altitude Air Shower Observatory (LHAASO), the square kilometer array, with 5249 electromagnetic particle detectors (EDs) and 1188 muon detectors, is deployed to explore the gamma-ray sources above 30 TeV with unprecedented sensitivity and to measure primary cosmic rays in the energy range from 10 TeV to 100 PeV. The energetic particles produced by extensive air showers can serve as a continuously available source for calibration of the numerous EDs over a large area. In this study, the detector untriggered probability is first proposed to estimate the particle density at different distances from the shower core and distinguish the characteristic single-particle signal detected by each ED. This method uses science data directly, and does not require prior knowledge of the cosmic-ray elemental composition or hadronic interaction model. Experimental results show that this self-calibration can be used to determine the number of particles detected by each ED with an accuracy better than 2% within a time scale of hours, which is adequate to meet the physics requirements of the LHAASO experiment. With this high efficiency and accuracy, this calibration also provides an ideal method to monitor the detector performance throughout an expected lifetime of >10 years.9 MoreReceived 15 April 2022Accepted 21 November 2022DOI:https://doi.org/10.1103/PhysRevD.106.122004© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic rays & astroparticlesTechniquesAstrophysical & cosmological simulationsCosmic ray & astroparticle detectorsMonte Carlo methodsProbability theoryScintillatorsAccelerators & BeamsGravitation, Cosmology & AstrophysicsParticles & Fields

Constraints on Heavy Decaying Dark Matter from 570Days of LHAASO Observations.

The kilometer square array (KM2A) of the large high altitude air shower observatory (LHAASO) aims at surveying the northern γ-ray sky at energies above 10TeV with unprecedented sensitivity. γ-ray observations have long been one of the most powerful tools for dark matter searches, as, e.g., high-energy γ rays could be produced by the decays of heavy dark matter particles. In this Letter, we present the first dark matter analysis with LHAASO-KM2A, using the first 340days of data from 1/2-KM2A and 230days of data from 3/4-KM2A. Several regions of interest are used to search for a signal and account for the residual cosmic-ray background after γ/hadron separation. We find no excess of dark matter signals, and thus place some of the strongest γ-ray constraints on the lifetime of heavy dark matter particles with mass between 10^{5} and 10^{9} GeV. Our results with LHAASO are robust, and have important implications for dark matter interpretations of the diffuse astrophysical high-energy neutrino emission.

Axion-Photon Conversion of LHAASO Multi-TeV and PeV Photons

Abstract The Large High Altitude Air Shower Observatory (LHAASO) has reported the detection of a large number of multi-TeV-scale photon events including also several PeV-scale gamma-ray-photon events with energy as high as 1.4 PeV. The possibility that some of these events may have extragalactic origins is not yet excluded. Here we propose a mechanism for the traveling of very-high-energy (VHE) and ultra-high-energy (UHE) photons based upon the axion-photon conversion scenario, which allows extragalactic above-threshold photons to be detected by observers on the Earth. We show that the axion-photon conversation can serve as an alternative mechanism, besides the threshold anomaly due to Lorentz invariance violation, for the very-high-energy features of the newly observed gamma ray burst GRB 221009A.

Axion-Photon Conversion of LHAASO Multi-TeV and PeV Photons

The Large High Altitude Air Shower Observatory (LHAASO) has reported the detection of a large number of multi-TeV-scale photon events also including several PeV-scale gamma-ray-photon events with energy as high as 1.4 PeV. The possibility that some of these events may have extragalactic origins is not yet excluded. Here we propose a mechanism for the traveling of very-high-energy and ultra-high-energy photons based upon the axion-photon conversion scenario, which allows extragalactic above-threshold photons to be detected by observers on the Earth. We show that the axion-photon conversation can serve as an alternative mechanism, besides the threshold anomaly due to Lorentz invariance violation, for the very-high-energy features of the newly observed gamma ray burst GRB 221009A.

Hadronuclear interactions in the jet of low TeV luminosity AGN: Implications for the low-state very-high-energy gamma-ray emission

In the study of radiation mechanisms of AGNs' jets, hadronuclear (pp) interactions are commonly neglected, because the number density of cold protons in the jet is considered insufficient. Very recently, our previous work proves that pp interactions in the low TeV luminosity AGNs, which have potential to generate detectable very-high-energy (VHE) emission, could be important. Based on this, the one-zone pp model is employed to study low-state quasi-simultaneous spectral energy distributions of a sample of low TeV luminosity AGNs in this work. Our modeling results show that the gamma-ray generated in pp interactions can explain the observed TeV spectra and has contribution to higher energy band that could be detected by the Large High Altitude Air Shower Observatory (LHAASO). In the sample, we suggest that M 87, Mrk 421 and Mrk 501 are the most likely objects to be detected by LHAASO in the near future. Other possible origins of VHE emission are also briefly discussed.

Investigating the [formula omitted]-ray properties for the pulsar wind nebula G75.2+0.1

Ultra-high-energy (UHE, E>0.1PeV) γ-ray sources emitting detected γ-rays with energies above 100 TeV in the Galaxy are potential candidates for the origin of the cosmic rays with energies up to 1 PeV. However, it is usually in debate whether the γ-rays are produced by protons/nuclei or electrons/positrons. Recently, photons with energies up to ∼0.27PeV from LHAASO J2018＋3651 have been detected with the Large High Altitude Air Shower Observatory (LHAASO). We investigate the origin of the γ-rays associated with the UHE source, and the detected fluxes can be reproduced via inverse Compton scattering of the electrons/positrons in the pulsar wind nebula (PWN) G75.2＋0.1. The electrons/positrons which have a spectrum of a power-law with cut-off energy powered due to spin-down of the pulsar are continuously injected into the nebula. Our results support that the UHE source originates from the PWN, and a detailed γ-ray spectrum in the range 10 TeV–1 PeV from future observations can give more insight concerning the cutoff pattern in the energy distribution of the particles injected into the nebula.

Constraining axion-like particles with the diffuse gamma-ray flux measured by the Large High Altitude Air Shower Observatory

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.

Joint photon-electron Lorentz violation parameter plane from LHAASO data

The Large High Altitude Air Shower Observatory (LHAASO) is one of the most sensitive gamma-ray detector arrays, whose ultrahigh-energy (UHE) work bands not only help to study the origin and acceleration mechanism of UHE cosmic rays, but also provide the opportunity to test fundamental physics concepts such as Lorentz symmetry. LHAASO directly observes the 1.42PeV highest-energy photon. By adopting the synchrotion self-Compton model, LHAASO also suggests that the 1.12PeV high-energy photon from Crab Nebula corresponds to a 2.3PeV high-energy electron. We study the 1.42PeV photon decay and the 2.3PeV electron decay to perform a joint analysis on photon and electron two-dimensional Lorentz violation (LV) parameter plane. Our analysis is systematic and comprehensive, and we naturally get the strictest constraints from merely considering photon LV effect in photon decay and electron LV effect in electron decay. Our result also permits the parameter space for new physics beyond relativity.

Flux variations of cosmic ray air showers detected by LHAASO-KM2A during a thunderstorm on June 10, 2021* *Supported in China by National Key R&D program of China (2018YFA0404201, 2018YFA0404202, 2018YFA0404203, 2018YFA0404204), NSFC (U2031101, 11475141, 12147208) and in Thailand by RTA6280002 from Thailand Science Research and Innovation

The Large High Altitude Air Shower Observatory (LHAASO) has three sub-arrays, KM2A, WCDA, and WFCTA. The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10, 2021. The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields, with a maximum fractional increase of 20%. The variations in trigger rates (increases or decreases) were found to be strongly dependent on the primary zenith angle. The flux of secondary particles increased significantly, following a trend similar to that of shower events. To better understand the observed behavior, Monte Carlo simulations were performed with CORSIKA and G4KM2A (a code based on GEANT4). We found that the experimental data (in saturated negative fields) were in good agreement with the simulations, assuming the presence of a uniform electric field of -700 V/cm with a thickness of 1500 m in the atmosphere above the observation level. Due to the acceleration/deceleration by the atmospheric electric field, the number of secondary particles with energy above the detector threshold was modified, resulting in the changes in shower detection rate.

Pulsars as candidates of LHAASO sources J2226+6057, J1908+0621, and J1825−1326

ABSTRACT The Large High Altitude Air Shower Observatory (LHAASO) Collaboration has observed ultrahigh-energy photons up to 1.4 PeV from 12 $\gamma$-ray Galactic sources. In particular, the γ-ray spectra of the sources J2226+6057, J1908+0621, and J1825−1326 have been published. We investigate the possibility of suggested origin pulsars near the sources as the PeVatrons. The pulsar is described by a rotating magnetic dipole. Assuming protons are uniformly distributed out of the light cylinders, we obtain the Lorentz distribution of proton energy spectrum. It is found that the protons around pulsar could be accelerated to PeV at short times. The hadronic γ-ray spectra of the suggested origin pulsars are in good agreement with the LHAASO observed γ-ray spectra of the sources J2226+6057, J1908+0621, and J1825−1326.

Slow Diffusion is Necessary to Explain the γ-Ray Pulsar Halos

It was suggested that the γ-ray halo around Geminga might not be interpreted by slow diffusion. If the ballistic regime of electron/positron propagation is considered, the Geminga halo may be explained even with a large diffusion coefficient. In this work, we examine this effect by taking the generalized Jüttner propagator as the approximate relativistic Green’s function for diffusion and find that the morphology of the Geminga halo can be marginally fitted in the fast-diffusion scenario. However, the recently discovered γ-ray halo around PSR J0622+3749 at the Large High-Altitude Air Shower Observatory cannot be explained by the same effect and slow diffusion is the only solution. Furthermore, both the two pulsar halos require a conversion efficiency from the pulsar spin-down energy to the high-energy electrons/positrons much larger than 100%, if they are interpreted by this ballistic transport effect. Therefore, we conclude that slow diffusion is necessary to account for the γ-ray halos around pulsars.

Exploring the Hadronic Origin of LHAASO J1908+0621

Recent observations by the Large High Altitude Air Shower Observatory (LHAASO) have paved the way for the observational detection of PeVatrons in the Milky Way, thus revolutionizing the field of γ-ray astrophysics. In this paper, we study one such detected source, LHAASO J1908+0621, and explore the origin of multi-TeV γ-ray emission from this source. A middle-aged radio supernova remnant SNR G40.5–0.5 and a GeV pulsar PSR J1907+0602 are cospatial with LHAASO J1908+0621. Dense molecular clouds are also found to be associated with SNR G40.5–0.5. We explain the multi-TeV γ-ray emission observed from the direction of LHAASO J1908+0621, by the hadronic interaction between accelerated protons that escaped from the SNR shock front and cold protons present inside the dense molecular clouds, and the leptonic emission from the pulsar wind nebula (PWN) associated with the pulsar J1907+0602. Moreover, we explain lower energy γ-ray emission by considering the radiative cooling of the electrons that escaped from SNR G40.5–0.5. Finally, the combined lepto-hadronic scenario was used to explain the multiwavelength spectral energy distribution of LHAASO J1908+0621. Although not yet significant, an IceCube hotspot of neutrino emission is spatially associated with LHAASO J1908+0621, indicating a possible hadronic contribution. In this paper, we show that if a hadronic component is present in LHAASO J1908+0621, then the second-generation IceCube observatory will detect neutrinos from this source.

Neutrino observations of LHAASO sources: Present constraints and future prospects

ABSTRACT The Large High Altitude Air Shower Observatory (LHAASO) observed a dozen gamma-ray sources with significant emission above 100 TeV that may be strong candidates for PeVatrons. Neutrino observations are crucial for diagnosing whether the gamma-ray radiative process is hadronic or leptonic. We use the Bayesian method to analyse the 10-yr (2008–2018) IceCube data, and hence constrain the hadronic gamma-ray emission in the LHAASO sources. The present neutrino data show that the hadronic gamma-ray flux from the Crab Nebula is lower than the observed gamma-ray flux at the 90 per cent confidence level and contributes less than 86 per cent, which disfavours the hadronic origin of gamma-rays below tens of TeV. For the other LHAASO sources, the present neutrino observations cannot put useful constraints on the gamma-ray radiative process. We consider the uncertainty of the source extension: the upper limits on the hadronic gamma-ray flux tend to increase with the extension; and some sources, namely LHAASO J2032+4102, LHAASO J1929+1745, and LHAASO J1908+0621, show a relatively high statistical significance of neutrino signals if the extension is ≲ 0.°6. Finally, we estimate the future observational results of LHAASO sources by proposed neutrino telescopes. If the LHAASO-observed PeV gamma-rays are of hadronic origin, the Crab Nebula may be detected at >100 TeV at the 3σ confidence level within 20 years by a neutrino detector with an effective area 30 times that of IceCube.

An asymmetrical model for high-energy radiation of Cassiopeia A

ABSTRACT The supernova remnant Cassiopeia A (Cas A) shows strong radiation from radio to gamma-ray bands. The mechanism of gamma-ray radiation in Cas A and its possible contribution to PeV cosmic rays are still under debate. The X-ray imaging reveals an asymmetric profile of Cas A, suggesting the existence of a jet-like structure. In this paper, we propose an asymmetrical model for Cas A, consisting of a fast moving jet-like structure and a slowly expanding isotropic shell. This model can account for the multiwavelength spectra of Cas A, especially for the power-law hard X-ray spectrum from ∼60 to 220 keV. The GeV to TeV emission from Cas A should be contributed by both hadronic and leptonic processes. Moreover, the jet-like structure may produce a gamma-ray flux of $\sim 10^{-13}\rm erg\, cm^{-2}\, s^{-1}$ at ∼100 TeV, to be examined by the Large High Altitude Air Shower Observatory (LHAASO) and the Cherenkov Telescope Array (CTA).

Testing Lorentz invariance of electrons with LHAASO observations of PeV gamma-rays from the Crab Nebula

The Large High Altitude Air Shower Observatory (LHAASO) recently reported the detection of gamma-ray emissions with energies up to 1.1PeV from the Crab Nebula. Using the absence of vacuum Cherenkov effect by inverse-Compton electrons, we improve previous bounds to linear-order Lorentz invariance violation (LV) in the dispersion relations of electrons by 104 times. We show that the LV effect on electrons is severely constrained, compatible with certain type of LV as expected by some models of quantum gravity (QG), such as the string/D-brane inspired space-time foam. We argue that such models are supported by the Crab Nebula constraints from the LHAASO observations, as well as various LV phenomenologies for photons to date.

Implications of gamma-ray photon measurements at the LHAASO on Lorentz symmetry * *Supported in part by the Natural Science Foundation of China (11875053, 12035016). Liu Yuxuan acknowledges the support from the National Postdoctoral Program for Innovative Talents (BX2021303), funded by China Postdoctoral Science Foundation

The Large High Altitude Air Shower Observatory (LHAASO) has reported the measurement of photons with high energies of up to 1.42 PeV from twelve gamma-ray sources. We are concerned with the implications of the LHAASO data on the fate of Lorenz symmetry at such high energy levels; thus, we consider the interaction between gamma rays and photons in the cosmic microwave background (CMB) and compute the optical depth, mean free path, and survival probability of photons from these gamma-ray sources. Employing the threshold value predicted by standard special relativity, the lowest survival probability for observed gamma ray photons is found to be approximately 0.60, which is fairly high and implies that abundant photons with energies above the threshold may reach the Earth without Lorentz symmetry violation. We conclude that it is unreasonable to argue that Lorentz symmetry would be violated using current observations at the LHAASO.

Ultrahigh-energy γ-Rays from Past Explosions in Our Galaxy

Abstract The discovery of the sources of ultrahigh-energy photons in our Galaxy by the High-Altitude Water Cherenkov Gamma-ray Observatory and the Large High Altitude Air Shower Observatory (LHAASO) has revolutionized the field of gamma-ray astronomy in the last few years. These emissions are sometimes found in the vicinity of powerful pulsars or supernova remnants (SNRs) associated with giant molecular clouds (GMCs). Inverse Compton emission by shock-accelerated electrons emitted by pulsars and proton–proton interactions of shock-accelerated protons emitted by SNRs with cold protons in molecular clouds are often identified as the causes of these emissions. In this paper we have selected two ultrahigh-energy photon sources, LHAASO J2108+5157 and LHAASO J0341+5258, which are associated with GMCs, but no powerful pulsar or SNR has been detected in their vicinity. We have proposed a scenario where shock-accelerated electrons and protons are injected in the local environment of these sources from past explosions, which happened thousands of years ago. We show that the observed ultrahigh-energy photon flux can be explained with the secondary gamma rays produced by the time-evolved relativistic electron and proton spectra.

Chapter 1 LHAASO Instruments and Detector technology * *Supported by National Natural Science Foundation in China (NSFC) (U2031103, U1831208, 11805209, 11775233), NSFC for Distinguished Young Scholars (12025502), the Science and Technology Department of Sichuan Province (2021YFSY0031) and the International Partnership Program of Chinese Academy of Sciences (113111KYSB20170055)

The Large High Altitude Air Shower Observatory (LHAASO) (Fig. 1) is located at Mt. Haizi (4410 m a.s.l., 600 g/cm2, 29° 21’ 27.56” N, 100° 08’ 19.66” E) in Daocheng, Sichuan province, P.R. China. LHAASO consists of 1.3 km2 array (KM2A) of electromagnetic particle detectors (ED) and muon detectors (MD), a water Cherenkov detector array (WCDA) with a total active area of 78,000 m2, 18 wide field-of-view air Cherenkov telescopes (WFCTA) and a newly proposed electron-neutron detector array (ENDA) covering 10,000 m2. Each detector is synchronized with all the other through a clock synchronization network based on the White Rabbit protocol. The observatory includes an IT center which comprises the data acquisition system and trigger system, the data analysis facility. In this Chapter, all the above-mentioned components of LHAASO as well as infrastructure are described.

Chapter 5 Dark Matter and New Physics Beyond the Standard Model with LHAASO

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.

Constraints on Hadronic Contributions to LHAASO Sources with Neutrino Observations

Abstract The Large High Altitude Air Shower Observatory (LHAASO) detected 12 gamma-ray sources above 100 TeV, which are the possible origins of Galactic cosmic-rays. We summarize the neutrino measurements by IceCube and ANTARES in the vicinity of LHAASO sources to constrain the contribution of hadronic gamma-rays in these sources. We find that the current observations constrain hadronic gamma-rays to contribute no more than ∼60% of the gamma-rays from the Crab Nebula. Gamma-rays from two LHAASO sources, LHAASO J1825−1326 and LHAASO J1907+0626, are dominated by leptonic components up to ∼200 TeV, under the hypotheses in the analysis by IceCube. The uncertainties of the constraint on the hadronic gamma-ray emission are discussed. We also constrain the total 100 TeV gamma-ray emission from TeV pulsar wind nebulae by relying on the remarkable sensitivity of LHAASO at that energy.