Y. J. Wang’s research while affiliated with Chinese Academy of Sciences and other places

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Publications (143)


An Enigmatic PeVatron in an Area around H ii Region G35.6−0.5
  • Article

January 2025

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7 Reads

The Astrophysical Journal

Zhen Cao

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F. Aharonian

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Axikegu

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[...]

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X. Zuo

Identifying Galactic PeVatrons (PeV particle accelerators) from ultrahigh-energy (UHE, >100 TeV) γ -ray sources plays a crucial role in revealing the origin of Galactic cosmic rays. The UHE source 1LHAASO J1857+0203u is suggested to be associated with HESS J1858+020, which may be attributed to the possible PeVatron candidate supernova remnant (SNR) G35.6−0.4 or H ii region G35.6−0.5. We perform detailed analysis on the very-high-energy and UHE γ -ray emissions toward this region with data from the Large High Altitude Air Shower Observatory (LHAASO). 1LHAASO J1857+0203u is detected with a significance of 11.6 σ above 100 TeV, indicating the presence of a PeVatron. It has an extent of ∼0 . ° 18 with a power-law (PL) spectral index of ∼2.5 at 1–25 TeV and pointlike emission with a PL spectral index of ∼3.2 above 25 TeV. Using archival CO and H i data, we identify some molecular and atomic clouds that may be associated with the TeV γ -ray emissions. Our modeling indicates that the TeV γ -ray emissions are unlikely to arise from clouds illuminated by the protons that escaped from SNR G35.6−0.4. In the scenario in which H ii region G35.6−0.5 could accelerate particles to the UHE band, the observed GeV–TeV γ -ray emission could be well explained by a hadronic model with a PL spectral index of ∼2.0 and cutoff energy of ∼450 TeV. However, an origin in an evolved pulsar wind nebula cannot be ruled out.


Deep view of composite SNR CTA1 with LHAASO in γ-rays up to 300 TeV

January 2025

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6 Reads

Science China Physics Mechanics and Astronomy

Zhen Cao

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F. Aharonian

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Axikegu

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[...]

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B. Li

The ultra-high-energy (UHE) gamma-ray source 1LHAASO J0007+7303u is positionally associated with the composite SNR CTA1 that is located at high Galactic Latitude b ≈ 10.5°. This provides a rare opportunity to spatially resolve the component of the pulsar wind nebula (PWN) and supernova remnant (SNR) at UHE. This paper conducted a dedicated data analysis of 1LHAASO J0007+7303u using the data collected from December 2019 to July 2023. This source is well detected with significances of 21σ and 17σ at 8–100 TeV and >100 TeV, respectively. The corresponding extensions are determined to be 0.23°±0.03° and 0.17°±0.03°. The emission is proposed to originate from the relativistic electrons accelerated within the PWN of PSR J0007+7303. The energy spectrum is well described by a power-law with an exponential cutoff function dN/dE=(42.4±4.1)(E20 TeV)2.31±0.11 exp(E110±25 TeV)dN/dE=(42.4\pm 4.1)({E\over 20\ \text{TeV}})^{-2.31\pm 0.11}\ \text{exp}(-{E\over 110\pm 25\ \text{TeV}}) TeV−1 cm−2 s−1 in the energy range from 8 to 300 TeV, implying a steady-state parent electron spectrum dNe/dEe (Ee100 TeV)3.13±0.16 exp[(Ee373±70 TeV)2]dN_{e}/dE_{e} \propto \ ({E_{e} \over 100\ \text{TeV}})^{-3.13\pm 0.16}\ \text{exp}[({-E_{e}\over373\pm 70\ \text{TeV}})^{2}] at energies above ≈ 50 TeV. The cutoff energy of the electron spectrum is roughly equal to the expected current maximum energy of particles accelerated at the PWN terminal shock. Combining the X-ray and gamma-ray emission, the current space-averaged magnetic field can be limited to ≈ 4.5 µG. To satisfy the multi-wavelength spectrum and the γ-ray extensions, the transport of relativistic particles within the PWN is likely dominated by the advection process under the free-expansion phase assumption.


Experimental observation of the periodic 2D modulated patterns in the BFO film grown on a LAO (001) substrate
a, High-resolution X-ray 2θ–ω scan showing the pseudocubic 002 peaks of the BFO/LAO (001) film, with the surrounding thickness fringes indicating the smooth surface of the BFO films. b, Local piezoresponse phase and amplitude hysteresis loops of the BFO film. c, Topography image (Topo.) of the 830 × 830 nm² region in the BFO film. d, DF TEM image of the BFO film showing the periodic distribution of dot-like contrast. e, Selected area electron diffraction pattern of the BFO film along the [001] zone axis. f, Under-focused atomic-resolved high-angle annular dark-field scanning TEM (HAADF-STEM) image of the BFO film, showing the dot-like contrast. g, Atomic-resolved electric vector colour map of the 2D modulated patterns. h, Sketch of the sample orientation with respect to the segmented detector, with the [100] and [010] directions of the BFO unit cells being parallel to the A–C and B–D segments of the detectors, respectively. i, Under-focused electric vector colour map showing the grid-like periodic 2D modulation patterns. The inset colour wheels in g and i represent the vector direction and magnitude by the colour and brightness, respectively. The rectangles in g and i highlight one modulation period.
Experimental polarization distribution of the periodic topological lattices in BFO films
a, Atomic-resolved HAADF-STEM image of the planar-view TEM sample with the 2D modulation patterns. b, Corresponding −δFe vector map of a. The rectangle in b defines a unit cell of the topological lattice. c, Schematic of the polarization distribution for one topological unit cell constituted by four centre-convergent domains. d, Averaged strain distribution (ε) map derived from geometric phase analysis, showing the 2D grid-like strain distribution. e, Cross-sectional atomic-resolved HAADF-STEM image viewed along the [11¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\bar{1}$$\end{document}0] direction of the BFO film. f, Corresponding −δFe vector map of e and the schematic illustration of polarization distribution. g, Reconstructed schematic of the polarization distribution for the centre-convergent domain (Skyrmion structure).
Experimental polarization distribution of the single-q topological state in BFO films
a, Schematic of the SE, HAADF and DPC-STEM imaging under the STEM mode. b, Atomic-resolved SE imaging of BFO films. c, Three-dimensional diagram of the enlarged cyan rectangle in b, showing the distribution of atomic columns. d, Corresponding FFT image of b with superstructure spots highlighted by black cycles. e, Atomic-resolved planar-view HAADF-STEM images of the 1D modulation fringes with the period of 2.2 nm. Inset: corresponding FFT pattern showing the superstructure spots. f, Corresponding −δFe vector map. g, Schematic illustration of the charged domain walls induced by 1D structural modulation, corresponding to the rectangle in f. Solid and broken lines in g denote the head-to-head and tail-to-tail charged domain walls, respectively. h, Under-focused DPC-STEM image showing the periodic electric field modulation of the single-q ordering.
The double-q topological lattice resultant from the intersection of two single-q topological dipole orderings
a, Atomic-resolved HAADF-STEM image of the planar-view TEM sample, showing the twin boundary derived from the intersection of two perpendicular 1D modulation fringes. The white dots denote the intersections. Insets: FFT patterns of the two 1D modulation fringes numbered with 1 and 2 in a. b, Corresponding −δFe vector map of a, showing the centre-convergent domains at the crosses. c,d, Magnified 1D modulation pattern (c) and skyrmion unit cell (d). e, Schematic illustration showing the formation of 2D SkX derived from the interaction of 1D modulation patterns. f,g, Under-focused iDPC-STEM (f) and DPC-STEM (g) maps, showing the formation of 2D modulation patterns derived from the intersection of two 1D modulation patterns. The colour wheel in g represents the vector direction and magnitude of local electric field by the colour and brightness, respectively. h–k, A series of DF TEM images showing the process of the topological phase transition from 1D modulation patterns to 2D modulation patterns under electron beam irradiation, which is highlighted by the red and green arrows. The irradiation time is increased from 0 min thereby the initial state (h), 3 min (i), 6 min (j) to 8 min (k). Note that all the DF TEM images were acquired in the same region as referenced with the cyan ellipses. l,m, FFT images of the DF TEM images in h and k, respectively, showing the transformation from single-q dipole wavevector to double-q dipole wavevector. n, Quantitative measurements of effective d33 for BFO films being 8 nm. o, Effective d33 versus BFO film thickness, where the DTD, SkX and SLD denote the diffused topological domains, skyrmion crystal and strike-like domains in different thicknesses, respectively.
The single-q and double-q topological polar orderings derived from phase-field simulations
a, Relaxed polarization configuration formed by two intersecting single-q states with 50% overlap. b, Planar polarization distribution at the interface between the single-q polar ordering and the double-q topological lattice configuration. c, Detailed three-dimensional polarization arrangement within the double-q lattice model. d, Specific depiction of the polarization structure of an individual skyrmion in the lattice. e, Planar view of the polarization distribution within the highlighted region of the lattice model. f, Corresponding topological charge density map of e, with the colour bar indicating the topological charge density in units of 1 nm⁻². The colours in the three-dimensional depiction indicate in-plane polarization angles with white for polarization pointing upwards and dark for polarization pointing downwards in the out-of-plane direction, as shown in the HSV colour sphere.
Dipolar wavevector interference induces a polar skyrmion lattice in strained BiFeO3 films
  • Article
  • Publisher preview available

January 2025

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67 Reads

Nature Nanotechnology

Skyrmions can form regular arrangements, so-called skyrmion crystals (SkXs). A mode with multiple wavevectors q then describes the arrangement. While magnetic SkXs, which can emerge in the presence of Dzyaloshinskii–Moriya interaction, are well established, polar skyrmion lattices are still elusive. Here we report the observation of polar SkXs with a well-defined double-q state in ultrathin BiFeO3 films on LaAlO3. The compressive strain induced by the LaAlO3 substrate yields a dipolar topological texture with a periodic arrangement of skyrmions. The square-like superstructure with a lattice constant of 2.68 nm features a periodic modulation of polarization fields and topological charge density. The film furthermore exhibits an enhanced electromechanical response with an increased converse piezoelectric coefficient (d33) compared with SkX-free films. Transmission electron microscopy experiments in combination with phase-field simulations indicate that the dipole skyrmion texture results from the interference of two orthogonal single-q dipole patterns. We anticipate that the interference of multiple wavevectors may lead to a diversity of topological crystals with a variety of symmetries and lattice constants.

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An Enigmatic PeVatron in an Area around HII Region G35.6-0.5

November 2024

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23 Reads

Identifying Galactic PeVatrons (PeV particle accelerators) from the ultra-high-energy (UHE, >100 TeV) γ\gamma-ray sources plays a crucial role in revealing the origin of Galactic cosmic rays. The UHE source 1LHAASO J1857+0203u is suggested to be associated with HESS J1858+020, which may be attributed to the possible PeVatron candidate supernova remnant (SNR) G35.6-0.4 or HII region G35.6-0.5. We perform detailed analysis on the very-high-energy and UHE γ\gamma-ray emissions towards this region with data from the Large High Altitude Air Shower Observatory (LHAASO). 1LHAASO J1857+0203u is detected with a significance of 11.6σ\sigma above 100 TeV, indicating the presence of a PeVatron. It has an extension of 0.18\sim 0.18^\circ with a power-law (PL) spectral index of \sim2.5 in 1-25 TeV and a point-like emission with a PL spectral index of \sim3.2 above 25 TeV. Using the archival CO and HI data, we identify some molecular and atomic clouds that may be associated with the TeV γ\gamma-ray emissions. Our modelling indicates that the TeV γ\gamma-ray emissions are unlikely to arise from the clouds illuminated by the protons that escaped from SNR G35.6-0.4. In the scenario that HII region G35.6-0.5 could accelerate particles to the UHE band, the observed GeV-TeV γ\gamma-ray emission could be well explained by a hadronic model with a PL spectral index of \sim2.0 and cutoff energy of \sim450 TeV. However, an evolved pulsar wind nebula origin cannot be ruled out.


FIG. 7. The attenuation length of the muon content varies with the flux cut. The bars represent statistical errors.
Measurement of attenuation length of the muon content in extensive air showers from 0.3 to 30 PeV with LHAASO

November 2024

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26 Reads

Physical Review D

The attenuation length of the muon content in extensive air showers provides important information regarding the generation and development of air showers. This information can be used not only to improve the description of such showers but also to test fundamental models of hadronic interactions. Using data from the LHAASO-KM2A experiment, the development of the muon content in high-energy air showers was studied. The attenuation length of muon content in the air showers was measured from experimental data in the energy range from 0.3 to 30 PeV using the constant intensity cut method. By comparing the attenuation length of the muon content with predictions from high-energy hadronic interaction models (-II-04, 2.3d, and -), it is evident that LHAASO results are significantly shorter than those predicted by the first two models (-II-04 and 2.3d) but relatively close to those predicted by the third model (-). Thus, the LHAASO data favor the - model over the other two models. The three interaction models confirmed an increasing trend in the attenuation length as the cosmic-ray energy increases. Published by the American Physical Society 2024


Detection of two TeV gamma-ray outbursts from NGC 1275 by LHAASO

November 2024

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16 Reads

Monthly Notices of the Royal Astronomical Society

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 hours per day with >98% 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 November 2022 and January 2023 with statistical significance of 5.2 σ and 8.3 σ. The observed spectral energy distribution in the range from 500 GeV to 3 TeV is fitted by a power-law with a best-fit spectral index of α = −3.37 ± 0.52 and −3.35 ± 0.29, respectively. The outburst flux above 0.5 TeV was (4.55±4.21)× 1011 cm2 s14.55\pm 4.21)\times ~10^{-11}~\rm cm^{-2}~s^{-1} and (3.45±1.78)× 1011 cm2 s13.45\pm 1.78)\times ~10^{-11}~\rm cm^{-2}~s^{-1}, corresponding to 60%, 45% of Crab Nebula flux. 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.


Figure 1. Significance maps of a 2° × 2° region around M87 by LHAASO-WCDA for the full time period (left panel), flare state (middle panel), and low state (right panel). M87 is marked by the cyan open cross. The gray circle indicates the 95% position error of the source. The white circle at the bottom-left corner shows the size of the LHAASO point-spread function (68% containment).
Figure 5. Fitting of the 1 day binned light curve (range from MJD 59593 to MJD 59629) of the VHE flare measured by LHAASO-WCDA with a two-sided exponential function (the red line). Fitting parameters are F 0 = (5.62 ± 1.26) × 10 −12 TeV −1 cm −2 s −1 , t 0 = MJD 59610 ± 0.58, t =  1.05 0.49 d rise
Best-fit Spectral Parameters of the LHAASO Data for Different Time Intervals
Best-fit Spectral Parameters of the Fermi-LAT Data
Detection of Very High-energy Gamma-Ray Emission from the Radio Galaxy M87 with LHAASO

November 2024

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39 Reads

The Astrophysical Journal Letters

The nearby radio galaxy M87 is a very high-energy (VHE) gamma-ray emitter established by observations with ground-based gamma-ray detectors. Here we report the long-term monitoring of M87 from 2021 to 2024 with the Large High Altitude Air Shower Observatory (LHAASO). M87 has been detected by LHAASO with a statistical significance ∼ 9 σ . The observed energy spectrum extends to 20 TeV, with a possible hardening at ∼20 TeV and then a clear softening at higher energies. Assuming that the intrinsic spectrum is described by a single power law up to 20 TeV, a tight upper bound on the extragalactic background light intensity is obtained. A strong VHE flare lasting 8 days, with a rise time of τ r rise = 1.05 ± 0.49 days and decay time of τ d decay = 2.17 ± 0.58 days, was found in early 2022. A possible GeV flare is seen also in Fermi Large Area Telescope data during the VHE flare period. The variability time as short as 1 day seen in the LHAASO data suggests a compact emission region with a size of ∼3 × 10 ¹⁵ δ cm ( δ being the Doppler factor of the emitting region), corresponding to a few Schwarzschild radii of the central supermassive black hole in M87. The continuous monitoring of the source reveals a duty cycle of ∼1% for VHE flares with a flux above 10 ⁻¹¹ erg cm ⁻² s ⁻¹ .


Figure 2 Left panel: One-dimensional distribution of γ ray flux of LHAASO J0248+6021. The blue (green) solid line represents the best-fitting model and the blue (green) shaded band is the ±1σ statistical uncertainty, which is the convolution of Eq. 1 (Gaussian model) with the PSF. Right panel: The θ d varies with the energy. The E in the legend represents the energy of the electrons. The result of the energy bin 1-25 TeV is derived from WCDA data, and those of energy bins 25-63 TeV and 63-251 TeV are derived from KM2A data, respectively.
Figure 3 Left panel: The energy spectrum of LHAASO J0248+6021. The solid line is the best-fit result assuming a log-parabola function, and the dotted line is the result of a single power-law. Right panel: SED fit results for different radiation models of LHAASO J0248+6021, and the green data ( 95% upper limits are derived from Fermi-LAT observations.
Figure 4 Left panel: The GeV residual TS map around PSR J0248+6021 in which the contribution of sources in the 4FGL-DR4 catalog are subtracted as background. Right panel: CO intensity map integrated over from −110 to 110 km s −1 using survey data from Dame et al.[25] (in unit of K km s −1 ). The green cross shows the position of PSR J0248+6021, and the green arrow shows the possible birth position of the pulsar given the direction and velocity of its transverse motion v T ∼ 500 km s −1 [10]. The dashed circle with radii of σ (the Gaussian disk models) obtained from WCDA data is shown in white and that from KM2A data is shown in magenta. The yellow contours show the CO intensity distribution integrated over the velocity range of −50 km s −1 to −30 km s −1 (W CO > 2 K km s −1 ) using data from Dame et al. [25].
Best-fit results of different radiation models described in Sec.4
Comparison of the properties of pulsars J0622+3749, Geminga, and Monogem.
LHAASO detection of very-high-energy gamma-ray emission surrounding PSR J0248+6021

October 2024

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39 Reads

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1 Citation

We report the detection of an extended very-high-energy (VHE) gamma-ray source coincident with the locations of middle-aged (62.4~\rm kyr) pulsar PSR J0248+6021, by using the LHAASO-WCDA data of live 796 days and LHAASO-KM2A data of live 1216 days. A significant excess of \gray induced showers is observed both by WCDA in energy bands of 1-25~\rm TeV and KM2A in energy bands of >> 25~\rm TeV with 7.3 σ\sigma and 13.5 σ\sigma, respectively. The best-fit position derived through WCDA data is R.A. = 42.06±^\circ \pm 0.12^\circ and Dec. = 60.24±^\circ \pm 0.13^\circ with an extension of 0.69±^\circ\pm0.15^\circ and that of the KM2A data is R.A.= 42.29±^\circ \pm 0.13^\circ and Dec. = 60.38±^\circ \pm 0.07^\circ with an extension of 0.37±^\circ\pm0.07^\circ. No clear extended multiwavelength counterpart of this LHAASO source has been found from the radio band to the GeV band. The most plausible explanation of the VHE \gray emission is the inverse Compton process of highly relativistic electrons and positrons injected by the pulsar. These electrons/positrons are hypothesized to be either confined within the pulsar wind nebula or to have already escaped into the interstellar medium, forming a pulsar halo.


Stringent Tests of Lorentz Invariance Violation from LHAASO Observations of GRB 221009A

August 2024

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76 Reads

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19 Citations

Physical Review Letters

On 9 October 2022, the Large High Altitude Air Shower Observatory (LHAASO) reported the observation of the very early TeV afterglow of the brightest-of-all-time gamma-ray burst 221009A, recording the highest photon statistics in the TeV band ever obtained from a gamma-ray burst. We use this unique observation to place stringent constraints on the energy dependence of the speed of light in vacuum, a manifestation of Lorentz invariance violation (LIV) predicted by some quantum gravity (QG) theories. Our results show that the 95% confidence level lower limits on the QG energy scales are EQG,1>10 times the Planck energy EPl for the linear LIV effect, and EQG,2>6×10−8EPl for the quadratic LIV effect. Our limits on the quadratic LIV case improve previous best bounds by factors of 5–7.


Citations (62)


... 1LHAASO J0249+6022 is an extended source detected simultaneously by (39% containment radius r 39 ≈ 0.71 • ) WCDA and (r 39 ≈ 0.38 • ) KM2A detectors, with a positional offset of ∼ 0.45 • (Cao et al. 2024a). Next, Cao et al. (2024b) observed excess γ-ray induced showers using the LHAASO-WCDA data of live 796 days and LHAASO-KM2A data of live 1216 days. In the case of a twodimensional Gaussian model, the best-fit position derived from WCDA data is R.A. = 42.06 • ± 0.12 • and Dec. = 60.24 ...

Reference:

Detection of the Extended $\gamma$-ray Emission around TeV source 1LHAASO J0249+6022 with Fermi-LAT
LHAASO detection of very-high-energy gamma-ray emission surrounding PSR J0248+6021

... The performance of LHAASO-KM2A have been studied in detail employing the Monte Carlo simulations 54 , and calibrated using the measurements of Crab Nebula as a standard candle 55 . The data quality control system and the long-term performance monitoring about the LHAASO-KM2A data can be found in 56 . ...

Data quality control system and long-term performance monitor of LHAASO-KM2A
  • Citing Article
  • August 2024

Astroparticle Physics

... At time t, the evolution of the total number of captured DM particles N (t) can be expressed as 6 It is worthwhile to mention here that though for the NFW parameters namely ρs and rs we use the above-mentioned expressions, we have also calculated the gamma-ray flux adopting the ρs and rs values directly from the various Refs. [56][57][58][59][60] and compared with those obtained from the analytical expressions and we find no significant changes in the main results. ...

Constraints on Ultraheavy Dark Matter Properties from Dwarf Spheroidal Galaxies with LHAASO Observations
  • Citing Article
  • August 2024

Physical Review Letters

... The number of events simulated by the QGSJET-II-04 model exceeded 7.1 × 10 7 , whereas the number of events simulated by EPOS-LHC and SIBYLL 2.3d exceeded 3.5 × 10 7 . The primary The ED and MD detector responses were simulated using the G4KM2A [17] package developed in the framework of Geant4 [18]. Random noise in a single ED and MD was also considered in the simulation. ...

LHAASO-KM2A detector simulation using Geant4
  • Citing Article
  • May 2024

Radiation Detection Technology and Methods

... Light particles have higher interaction cross-sections with these fields, leading to more frequent production of secondary photons than occurs with heavier nuclei [10]. Recent studies using the data acquired by the Large High Altitude Air Shower Observatory (LHAASO) suggest that the average cosmic-ray mass is heavier than helium at around 10 16 eV with an increasing trend towards heavier elements up to about 2 × 10 17 eV [11], after which the composition either remains constant or becomes lighter [12][13][14][15][16][17]. ...

Measurements of All-Particle Energy Spectrum and Mean Logarithmic Mass of Cosmic Rays from 0.3 to 30 PeV with LHAASO-KM2A

Physical Review Letters

... γ-ray emissions can arise from hadronic interactions, where π 0 decays into two γ-ray photons, through inverse Compton (IC) scattering, or via nonthermal bremsstrahlung radiation from high-energy electrons. γ-ray emissions from SNRs and PWNe have been extensively observed by space telescopes, particularly the Large Area Telescope (LAT) aboard the Fermi satellite, and ground-based Cherenkov telescopes such as H.E.S.S. (Aharonian et al. 2004), VERITAS (Holder et al. 2006), MAGIC (Aleksić et al. 2016), HAWC (Abeysekara et al. 2013), and LHAASO (Cao et al. 2024). Detailed studies of these γ-ray SNRs and PWNe are crucial for understanding the acceleration and radiation processes of particles, and for further elucidating the origin of CRs. ...

The First LHAASO Catalog of Gamma-Ray Sources

The Astrophysical Journal Supplement Series

... Located at a distance of 3.4 kpc, this source has a diameter of around 5 pc (Kassim et al. 1995;Reed et al. 1995). As one of the brightest galactic radio sources, Cas A has been extensively studied across various wavelengths from radio to X-rays, and up to ultra-high-energy γ-ray band (Cao et al. 2024a). ...

Does or Did the Supernova Remnant Cassiopeia A Operate as a PeVatron?

The Astrophysical Journal Letters

... Also, the spectrum of gamma rays from the clouds may provide insights into particle acceleration at the source and the particle transport around the source. Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported the discovery of a giant UHE gamma-ray bubble in the star-forming region Cygnus X [11], which was suggested to be an efficient CR factory [12,13]. The gamma-ray spectrum extends up to 2 PeV without showing a clear cutoff feature, suggesting the existence of a super-PeVatron. ...

An ultrahigh-energy γ -ray bubble powered by a super PeVatron
  • Citing Article
  • December 2023

Science Bulletin

... % NaOH solution and corresponding EDSelemental mapping distributionno second current transient occurred during metastable formation, suggesting that some surface inclusions remained dissolved state. This implies a decreased probability of pitting breakdown with extended potentiostatic polarization duration[48,49]. ...

Improving pitting resistance of Mo-containing stainless steels via chloride-assisted stabilization of the passive film
  • Citing Article
  • December 2023

Corrosion Science