Fault Detection and Diagnosis Software of LHAASO

The LHAASO~J2018+3651 region is one of the brightest sources in the sky at TeV energies. Photons with energies up to ∼0.27 PeV from this region have been detected with the Large High Altitude Air Shower Observatory (LHAASO) and here we present a detailed study of this region using more data from LHAASO. This analysis resolves the region into six sources: LHAASO~J2018+3641, LHAASO~J2019+3649, LHAASO~J2021+3657, LHAASO~J2016+3712, LHAASO~J2013+3610 and LHAASO~J2028+3655. An investigation of the morphology and spectrum for LHAASO~J2018+3641, LHAASO~J2019+3649 and LHAASO~J2021+3657 are the focus and we find that the spectrum above TeV deviates significantly from a single power-law, and is best described by a power-law with exponential cutoff. The three sources may be associated with PSR~J2021+3651 and its X-ray pulsar wind nebula. Additionally, LHAASO~J2016+3712 is tentatively associated with the evolved supernova remnant CTB 87.

Introduction to Large High Altitude Air Shower Observatory (LHAASO)

Status of the large high altitude air shower observatory project

Large High Altitude Air Shower Observatory (LHAASO) is a composite cosmic ray observatory consisting of three types of detectors: KM2A, WCDA and WFCTA. One of the main scientific objectives of LHAASO is to measure the cosmic ray spectrum and composition precisely. With hybrid detection of WCDA and WFCTA, one can further study the Knee of cosmic rays from 100TeV to 10PeV. The original components of cosmic rays can be effectively distinguished with four parameters provided by WFCTA, WCDA and MDA, respectively. The energy reconstruction resolution of proton shower is about 20% reconstructed only by WFCTA. Combining with the energy flow of shower core provided by WCDA, a better energy resolution is expected.

Diffuse γ-ray emission between 10 and 1000 TeV from the Galactic plane was recently measured by the Large High Altitude Air Shower Observatory (LHAASO). These observations will help tremendously in constraining the propagation and interaction of cosmic rays in the Milky Way. Additionally, new measurements of cosmic-ray spectra reach a very high precision of up to 100 TeV energies, revealing multiple spectral structures of various species. In this work, based on up-to-date measurements of local cosmic-ray spectra and a simplified propagation setup, we confront a model prediction of diffuse γ-ray emission with measurements of diffuse γ-rays. To better constrain the low-energy part of the model, we analyze the 14.6 yr of Fermi Large Area Telescope (Fermi-LAT) data to extract the Galactic diffuse emission between 1 and 500 GeV from the same sky regions of LHAASO, after subtracting the contribution from known sources and the isotropic diffuse γ-ray background. The joint Fermi-LAT and LHAASO spectra thus cover a very wide energy range from 1 GeV to 1 PeV with small gaps from 0.5 to 10 TeV. Compared with the prediction, we find that clear excesses between several GeV and ∼60 TeV of the diffuse emission exist. Possible reasons to explain the excesses may include unresolved sources or more complicated propagation models. We illustrate that an exponential cutoff power-law component with an index of −2.40 and a cutoff energy of ∼30 TeV is able to account for such excesses.

The Large High Altitude Air Shower Observatory (LHAASO) experiment, fully operational since July 2021, is a cutting-edge facility for detecting cosmic rays and gamma rays across a wide energy range. This paper offers an overview of the current status and recent significant scientific achievements of the LHAASO collaboration. These include the gamma-ray astronomy, charged cosmic ray physics and new physics.

We investigate the extinction coefficients of the surface atmospheric aerosol over the Large High Altitude Air Shower Observatory (LHAASO), located at the Haizi Mountain, Daocheng County, China. To this end, we utilize the Longtin model, Mie scattering theory, and experimental data obtained by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Our theoretical calculations show that the total extinction coefficients of the atmospheric aerosol at the wavelength of 200–500 nm are inversely proportional to the laser wavelength, and influenced by the wind speed. From July 2015 to October 2016, the extinction coefficient of the surface atmospheric aerosols at 532 nm wavelength reached 0.04 km−1 with no wind, while it increased to 0.1 km−1 with gusts. In this period, the extinction coefficients of the surface atmospheric aerosol at 532 nm wavelength, obtained by the CALIPSO, change from 0.01 to 0.07 km−1, which is less than the values obtained the theoretical calculation and larger than the average of Tibetan Plateau in 2006−2016. These calculations and experimental evidence provide important arguments to the model of atmospheric aerosol to be applied in the calibration of LHAASO. Our results suggest that the extinction coefficients over LHAASO require further study, including research on the size distribution, shape, concentration of aerosols particles, wind dependence, relative humidity dependence, etc.

Based on 42 months of observations by the Large High Altitude Air Shower Observatory(LHAASO), we report on the active behavior of the blazar Mrk 501, which exhibited several high states during this period. The most dramatic flare occurred between MJD 59334 and MJD 59348, reaching 62% of the Crab Nebula flux (> 1 TeV). The global spectral energy distribution (SED) of Mrk 501 above 1 TeV is well described by a power-law model with an exponential cutoff, yielding a power-law index of 𝛼 = 2.18 ± 0.04 and a cutoff energy of 𝐸cut = 9.51 ± 1.44 TeV. Ongoing studies focus on multi-wavelength correlations and broadband spectral modeling to further understand the underlying physical mechanisms driving these phenomena. LHAASO's all-weather capability and high duty cycle provide critical continuous data for such investigations.

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.

Context. The first Large High Altitude Air Shower Observatory (LHAASO) catalog presents six enigmatic ultra-high-energy (UHE) γ-ray sources with lonely > 25 TeV emission being detected, which are indicated as 1LHAASO: J0007+5659u, J0206+4302u, J0212+4254u, J0216+4237u, J1740+0948u, and J1959+1129u. No counterparts of the six sources have been observed except two energetic pulsars, PSR J0218+4232 and PSR J1740+1000. Among them, 1LHAASO: J0206+4302u, J0212+4254u, and J0216+4237u are connected on the significance map and constitute a dumbbell-like structure. They are close in position and show a similar spectral shape, suggesting a physical association among them. Aims. To explain the origin of the six LHAASO sources, especially the intriguing dumbbell-like structure, we conducted leptonic and hadronic modeling research according to our multiwavelength and multimessenger study. For the dumbbell-like structure, models with traveling pulsar wind nebulae (PWNe) were considered. Methods. The multiwavelength and multimessenger study was based on the Fermi-LAT, Swift-XRT, Planck, CfA 12CO survey, and IceCube neutrino datasets. In the traveling PWN modeling research, we assumed an isotropic and homogeneous diffusion condition and discussed the influence of the diffusion coefficient, distance, and proper motion velocity. Results. We do not discover any counterparts in the multiwavelength and multimessenger study except the two known pulsars. The traveling PWN modeling attempt with a single PWN appears to be implausible for explaining the dumbbell-like structure, as the diffusion coefficient needs to be much lower than the Bohm limit. We also explored a double traveling PWNe model, and it could account for the results of the LHAASO observations. However, the probability of the occurrence of this explanation is significantly lower than that of a conventional triple PWNe explanation. Furthermore, according to our model, the only known pulsar, PSR J0218+4232, is unlikely to be associated with the dumbbell-like structure in an isotropic and homogeneous diffusion environment. The expected teraelectronvolt emission of this pulsar is far from explaining even the eastern part of the structure.

The Water Cherenkov Detector Array (WCDA) is one of the components of Large High Altitude Air Shower Observatory (LHAASO) and can monitor any sources over two-thirds of the sky for up to 7 h per day with >98 per cent duty cycle. In this work, we report the detection of two outbursts of the Fanaroff–Riley I radio galaxy NGC 1275 that were detected by LHAASO-WCDA between 2022 November and 2023 January with statistical significance of 5.2$\sigma$ and 8.3$\sigma$. The observed spectral energy distribution in the range from 500 GeV to 3 TeV is fitted by a power law with the best-fitting spectral index of $\alpha =-3.37\pm 0.52$ and $-3.35\pm 0.29$, respectively. The outburst flux above 0.5 TeV was ($4.55\pm 4.21)\times 10^{-11}~\rm cm^{-2}~s^{-1}$ and ($3.45\pm 1.78)\times 10^{-11}~\rm cm^{-2}~s^{-1}$, corresponding to 60 per cent and 45 per cent of Crab Nebula flux, respectively. Variation analysis reveals the variability time-scale of days at the TeV energy band. A simple test by one-zone synchrotron self-Compton model reproduces the data in the gamma-ray band well.

The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the EBL density directly is challenging. However, gamma-ray astronomy provides an alternative approach to indirectly studying the EBL through the observation of gamma-ray absorption in the spectra of distant blazars. The Large High Altitude Air Shower Observatory (LHAASO), with its unique capabilities --- near full duty cycle, wide field of view, and high sensitivity -- is exceptionally well-suited for exploring the EBL, particularly in the near to mid-infrared region (wavelengths of 1 to 100 micrometers). In this presentation, we will discuss the methods we employed for data analysis and share our preliminary findings.

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.

Recently, two photons from the Crab Nebula with energy of approximately 1 PeV were detected by the Large High Altitude Air Shower Observatory (LHAASO), opening an ultrahigh-energy window for studying pulsar wind nebulae (PWNe). Remarkably, the LHAASO spectrum at the highest-energy end shows a possible hardening, which could indicate the presence of a new component. A two-component scenario with a main electron component and a secondary proton component has been proposed to explain the whole spectrum of the Crab Nebula, requiring a proton energy of 1046–1047 erg remaining in the present Crab Nebula. In this paper, we study the energy content of relativistic protons in pulsar winds using the LHAASO data of the Crab Nebula, considering the effect of diffusive escape of relativistic protons. Depending on the extent of the escape of relativistic protons, the total energy of protons lost in the pulsar wind could be 10–100 times larger than that remaining in the nebula presently. We find that the current LHAASO data allow up to (10–50)% of the spindown energy of pulsars being converted into relativistic protons. The escaping protons from PWNe could make a considerable contribution to the cosmic-ray flux of 10–100 PeV. We also discuss the leptonic scenario for the possible spectral hardening at PeV energies.