L. Q. Gao

Vanderbilt University

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Xiao-Jun Bi

Chinese Academy of Sciences

Li-Sheng Geng

Beihang University

D. Kuleshov

Institute for Nuclear Research

Z. G. Yao

Chinese Academy of Sciences

Lili Yang

Sun Yat-sen University

K. K. Duan

Purple Mountain Observatory

Z. Y. Pei

Guangzhou University

D. Bastieri

Guangzhou University

D. della Volpe

University of Geneva

T. Ke

Institute of High Energy Physics

Cooperative Institutions

Chinese Academy of Sciences

910

Institute of High Energy Physics

606

University of Chinese Academy of Sciences

374

University of Science and Technology of China

244

Campbell Collaboration

229

Southwest Jiaotong University

226

Gansu Great Wall Electrical and Electronics Engineering Research Institute

190

Purple Mountain Observatory

149

Shandong University

137

Nanjing University

128

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Very high energy gamma-ray emission beyond 10 TeV from GRB 221009A

arXiv (Cornell University) (2023)

Z. Cao F Aharonian Qi An A. Axikegu Y. X. Bai

The highest energy gamma-rays from gamma-ray bursts (GRBs) have important implications for their radiation mechanism. Here we report for the first time the detection of gamma-rays up to 13 TeV from the brightest GRB 221009A by the Large High Altitude Air-shower Observatory (LHAASO). The LHAASO-KM2A detector registered more than 140 gamma-rays with energies above 3 TeV during 230$-$900s after the trigger. The intrinsic energy spectrum of gamma-rays can be described by a power-law after correcting for extragalactic background light (EBL) absorption. Such a hard spectrum challenges the synchrotron self-Compton (SSC) scenario of relativistic electrons for the afterglow emission above several TeV. Observations of gamma-rays up to 13 TeV from a source with a measured redshift of z=0.151 hints more transparency in intergalactic space than previously expected. Alternatively, one may invoke new physics such as Lorentz Invariance Violation (LIV) or an axion origin of very high energy (VHE) signals.

Air shower

Extragalactic background light

10.48550/arxiv.2310.08845

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Citations (3)

Exploring Constraints on Axion-like Particles with the Observations for blazar Mrk 501

arXiv (Cornell University) (2025)

Tao Zhou L. Q. Gao Xiao-Jun Bi Peng-Fei Yin Wenbin Lin

Oscillations between axion-like particles (ALPs) and photons in astrophysical magnetic fields can lead to irregularities in the high energy gamma ray spectra of blazars. The magnetic field within the blazar jet plays a crucial role in shaping these effects, with its strength in the emission region being an important parameter determined by multi-wavelength observations. However, the origin of the high energy bump observed in the spectral energy distribution of some blazars is a topic of debate, with both leptonic and hadronic scenarios providing plausible explanations that result in different magnetic field strengths in the emission region. In this study, we investigate the impact of magnetic field configurations on the constraints of ALP parameters. We consider both leptonic and hadronic emission scenarios for the blazar Mrk 501 and derive the corresponding jet magnetic field strengths. Additionally, we explore two jet magnetic field models: one with a toroidal component and the other with helical and tangled components. By analyzing the spectra of Mrk 501 observed by MAGIC and Fermi-LAT from 2017-06-17 to 2019-07-23, which are well-described by both emission scenarios, we derive constraints on the ALP parameters. Our results demonstrate that both the emission scenario and the magnetic field structure play a significant role in deriving these constraints, with the hadronic model leading to much more stringent limits compared to the leptonic model.

10.48550/arxiv.2501.18860

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Constraints on Axion-like Particles from Observations of Mrk 421 using the ${\rm CL_s}$ Method

arXiv (Cornell University) (2023)

L. Q. Gao Xiao-Jun Bi J. G. Guo Wenbin Lin Peng‐Fei Yin

Axion-like particles (ALPs) may undergo mixing with photons in the presence of astrophysical magnetic fields, leading to alterations in the observed high energy $\gamma$-ray spectra. In this study, we investigate the ALP-photon oscillation effect using the spectra of the blazar Mrk 421 over 15 observation periods measured by Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) and Fermi Large Area Telescope (Fermi-LAT). Compared with previous studies, we generate mock data under the ALP hypothesis and employ the ${\rm CL_s}$ method to set constraints on the ALP parameters. This method is widely utilized in high energy experiments and avoids the exclusion of specific parameter regions where distinguishing between the null and ALP hypotheses is challenging. We find that the ALP-photon coupling $g_{a\gamma}$ is constrained to be smaller than $\sim 2\times10^{-11}$ GeV$^{-1}$ for ALP masses ranging from $10^{-9}$ eV to $10^{-7}$ eV at the 95\% confidence level. We also present the constraints derived from the TS distribution under the null hypothesis, which is commonly utilized in previous astrophysical ALP studies. Our results reveal that the combined constraints of all the periods obtained from both methods are consistent. However, the ${\rm CL_s}$ method remains effective in cases where the latter method fails to provide constraints for specific observation periods.

Null (SQL)

Cherenkov Telescope Array

10.48550/arxiv.2309.02166

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

The Astrophysical Journal Letters (2024)

Z. Cao F. Aharonian Q. An Axikegu Y. X. Bai

Abstract For decades, supernova remnants (SNRs) have been considered the prime sources of Galactic cosmic rays (CRs). But whether SNRs can accelerate CR protons to PeV energies and thus dominate CR flux up to the knee is currently under intensive theoretical and phenomenological debate. The direct test of the ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy (UHE; E γ ≥ 100 TeV) γ -rays. In this context, the historical SNR Cassiopeia A (Cas A) is considered one of the most promising targets for UHE observations. This paper presents the observation of Cas A and its vicinity by the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE band, combined with the young age of Cas A, enabled us to derive stringent model-independent limits on the energy budget of UHE protons and nuclei accelerated by Cas A at any epoch after the explosion. The results challenge the prevailing paradigm that Cas A–type SNRs are major suppliers of PeV CRs in the Milky Way.

Cassiopeia A

10.3847/2041-8213/ad1d62

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Citations (1)

Movie Gen: A Cast of Media Foundation Models

arXiv (Cornell University) (2024)

Adam Polyak Amit Zohar Andrew H. Brown Andros Tjandra Animesh A. Sinha

We present Movie Gen, a cast of foundation models that generates high-quality, 1080p HD videos with different aspect ratios and synchronized audio. We also show additional capabilities such as precise instruction-based video editing and generation of personalized videos based on a user's image. Our models set a new state-of-the-art on multiple tasks: text-to-video synthesis, video personalization, video editing, video-to-audio generation, and text-to-audio generation. Our largest video generation model is a 30B parameter transformer trained with a maximum context length of 73K video tokens, corresponding to a generated video of 16 seconds at 16 frames-per-second. We show multiple technical innovations and simplifications on the architecture, latent spaces, training objectives and recipes, data curation, evaluation protocols, parallelization techniques, and inference optimizations that allow us to reap the benefits of scaling pre-training data, model size, and training compute for training large scale media generation models. We hope this paper helps the research community to accelerate progress and innovation in media generation models. All videos from this paper are available at https://go.fb.me/MovieGenResearchVideos.

Foundation (evidence)

10.48550/arxiv.2410.13720

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Flux variations of cosmic ray air showers detected by LHAASO-KM2A during a thunderstorm on June 10, 2021*

Chinese Physics C (2022)

F. Aharonian Q. An Ling Bai Y. Bai Yiwang Bao

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 the thunderstorm on 10 June 2021. The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields, with maximum fractional increase of 20%. The variations of trigger rates (increases or decreases) are found to be strongly dependent on the primary zenith angle. The flux of secondary particles increases significantly, following a similar trend with that of the shower events. To better understand the observed behavior, Monte Carlo simulations are performed with CORSIKA and G4KM2A (a code based on GEANT4). We find that the experimental data (in saturated negative fields) are in good agreement with simulations, assuming the presence of a uniform upward electric field of 700 V/cm with a thickness of 1500 m in the atmosphere above the observation level. Due to the acceleration/deceleration and deflection by the atmospheric electric field, the number of secondary particles with energy above the detector threshold is modified, resulting in the changes in shower detection rate.

Air shower

Zenith

Shower

10.1088/1674-1137/ac9371

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Citations (5)

Absolute calibration of LHAASO WFCTA camera based on LED

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (2021)

F. Aharonian Qi An Axikegu Lixin Bai Y. Bai

Air shower

10.1016/j.nima.2021.165824

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Citations (16)

An Ultrahigh-energy $γ$-ray Bubble Powered by a Super PeVatron

arXiv (Cornell University) (2023)

Zhen Cao F Aharonian Qi An M Axikegu Y. X. Bai

We report the detection of a $\gamma$-ray bubble spanning at least 100$\rm deg^2$ in ultra high energy (UHE) up to a few PeV in the direction of the star-forming region Cygnus X, implying the presence Super PeVatron(s) accelerating protons to at least 10 PeV. A log-parabola form with the photon index $\Gamma (E) = (2.71 \pm 0.02) + (0.11 \pm 0.02) \times \log_{10} (E/10 \ {\rm TeV})$ is found fitting the gamma-ray energy spectrum of the bubble well. UHE sources, `hot spots' correlated with very massive molecular clouds, and a quasi-spherical amorphous $\gamma$-ray emitter with a sharp central brightening are observed in the bubble. In the core of $\sim 0.5^{\circ}$, spatially associating with a region containing massive OB association (Cygnus OB2) and a microquasar (Cygnus X-3), as well as previously reported multi-TeV sources, an enhanced concentration of UHE $\gamma$-rays are observed with 2 photons at energies above 1 PeV. The general feature of the bubble, the morphology and the energy spectrum, are reasonably reproduced by the assumption of a particle accelerator in the core, continuously injecting protons into the ambient medium.

Particle (ecology)

10.48550/arxiv.2310.10100

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Citations (3)

Method to measure muon content of extensive air showers with LHAASO KM2A-WCDA synergy

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (2023)

Z. Cao F. Aharonian Qi An Axikegu Lixin Bai

Cherenkov detector

Air shower

10.1016/j.nima.2023.168958

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Impact of Parameters in the Blazar Jet Magnetic Field Model on Axion-Like Particle Constraints

arXiv (Cornell University) (2024)

L. Q. Gao Xiao-Jun Bi Jun Li Peng-Fei Yin

The interaction between axion-like particles (ALPs) and photons induces ALP-photon oscillations in astrophysical magnetic fields, leading to spectral distortions in the $\gamma$-ray spectrum of blazars. The primary uncertainty of this phenomenon may originate from the magnetic field within the jet of the blazar. While many studies have explored the effects of ALP-photon oscillations using typical values for jet magnetic field parameters, it is important to recognize that these parameters can be constrained by multi-wavelength observations. In this study, we utilize the high energy $\gamma$-ray spectrum of Mrk 421 obtained from MAGIC and Fermi-LAT observations. By employing multi-wavelength fitting with a one-zone synchrotron self-Compton model, we derive the parameters characterizing the magnetic field model within the jet, and investigate their impacts on the ALP constraints.

Particle (ecology)

10.48550/arxiv.2407.20118

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Citations (0)