Ultra-high-energy Gamma-ray Research Articles

Detection prospects of very and ultra high-energy gamma rays from extended sources with ASTRI, CTA, and LHAASO

Context. The recent discovery of several ultra high-energy gamma-ray emitters in our Galaxy represents a significant advancement towards the characterisation of its most powerful accelerators. Nonetheless, in order to unambiguously locate the regions where the highest energy particles are produced and understand the responsible physical mechanisms, detailed spectral and morphological studies are required, especially given that most of the observed sources were found to be significantly extended. Aims. In these regards, pointing observations with the next-generation Imaging Atmospheric Cherenkov Telescopes, such as the Cherenkov Telescope Array (CTA) Observatory and the ASTRI Mini-Array (ASTRI), are expected to provide significant improvements. Here we aim to identify the most promising sources to target in future observations. Methods. For this purpose, we performed a comparative analysis of the expected performance of ASTRI and CTA, computing their differential sensitivities towards extended sources, and further explored their capabilities with respect to specific case studies, including follow-ups of existing gamma-ray source catalogues. Results. We find that almost all of the sources thus far detected by LHAASO-WCDA and in the H.E.S.S. Galactic Plane Survey will be in the reach of ASTRI and CTA with about 300 and 50 hours of exposure, respectively. For the highest energy emitters detected by LHAASO-KM2A, in turn, we provide a list of the most promising objects that would require further investigation. We additionally examined specific classes of sources in order to identify potentially detectable gamma-ray emitters, such as passive molecular clouds (i.e. illuminated by the cosmic-ray sea) and pulsars surrounded by a halo of runaway particles.

Observation of the Galactic Center PeVatron beyond 100 TeV with HAWC

We report an observation of ultrahigh-energy (UHE) gamma rays from the Galactic center (GC) region, using 7 yr of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum ( dN/dE=ϕE/26TeVγ ), where γ = −2.88 ± 0.15stat − 0.1sys and ϕ = 1.5 × 10−15 (TeV cm2 s)−1 ±0.3stat−0.13sys+0.08sys extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to 100 TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A* (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant (>5σ), with the spectrum extending to >100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the GC.

On the inefficiency of particle re-acceleration mechanisms in the cores of massive stellar clusters

ABSTRACT We consider scenarios for non-thermal particle acceleration and re-acceleration in the central cores of compact massive star clusters, aided by insights from high-resolution hydrodynamic simulations. We show that (i) particles are unlikely to interact with many shocks during their lifetimes in the core; (ii) colliding flows do not produce hard spectra; and (iii) turbulent re-acceleration in the core is suppressed. Inefficient re-acceleration mechanisms are not expected to produce hard components nor to increase the maximum energy within the cores of massive star clusters. Models in which the observed ultra-high-energy gamma rays originate in the core of massive stellar clusters are thus disfavoured.

Constraints on axion-like particles from the observation of Galactic sources by the LHAASO* *Xiao-Jun Bi is supported by the National Natural Science Foundation of China (12175248). Xiaoyuan Huang is supported by the National Key Research and Development Program of China (2022YFF0503304), the National Natural Science Foundation of China (12322302), the Project for Young Scientists in Basic Research of Chinese Academy

High-energy photons may oscillate with axion-like particles (ALPs) when they propagate through the Milky Way's magnetic field, resulting in an alteration in the observed photon energy spectrum. Ultra-high energy gamma-ray spectra, measured by the Large High Altitude Air Shower Observatory (LHAASO) up to , provide a promising opportunity to investigate the ALP-photon oscillation effect. In this study, we utilize the gamma-ray spectra of four Galactic sources measured by the LHAASO, that is, the Crab Nebula, LHAASO J2226+6057, LHAASO J1908+0621, and LHAASO J1825-1326, to explore this effect. We employ the CLs method to set constraints on the ALP parameters. Our analysis of the observations of the four sources reveals that the ALP-photon coupling is constrained to be smaller than for an ALP mass of at 95% C.L. Combining the observations of the Crab Nebula from the LHAASO and other experiments, we find that the ALP-photon coupling may be set to approximately for an ALP mass of , which is similar to the CAST constraint.

Constraints on the proton fraction of cosmic rays at the highest energies and the consequences for cosmogenic neutrinos and photons

Over the last decade, observations have shown that the mean mass of ultra-high-energy cosmic rays (UHECRs) increases progressively toward the highest energies. However, the precise composition is still unknown and several theoretical studies hint at the existence of a subdominant proton component up to the highest energies. Motivated by the exciting prospect of performing charged-particle astronomy with ultra-high-energy (UHE) protons we quantify the level of UHE-proton flux that is compatible with present multimessenger observations and the associated fluxes of neutral messengers produced in the interactions of the protons. We study this scenario with numerical simulations of two independent populations of extragalactic sources and perform a fit to the combined UHECR energy spectrum and composition observables, constrained by diffuse gamma-ray and neutrino observations. We find that up to of order 10% of the cosmic rays at the highest energies can be UHE protons, although the result depends critically on the selected hadronic interaction model for the air showers. Depending on the maximum proton energy (E max p) and the redshift evolution of sources, the associated flux of cosmogenic neutrinos and UHE gamma rays can significantly exceed the multimessenger signal of the mixed-mass cosmic rays. Moreover, if E max p is above the GZK limit, we predict a large flux of UHE neutrinos above EeV energies that is absent in alternate scenarios for the origin of UHECRs. We present the implications and opportunities afforded by these UHE proton, neutrino and photon fluxes for future multimessenger observations.

Probing LHAASO galactic PeVatrons through gamma-ray and neutrino correspondence

ABSTRACT Recently, Large High Altitude Air Shower Observatory (LHAASO) has detected several Galactic point sources of ultra high energy (UHE; Eγ > 100 TeV) gamma-rays. These gamma-rays are possibly created in leptonic or hadronic interactions of cosmic rays (CRs) of PeV energies. In the hadronic channel (p − p interaction), the gamma-rays are accompanied by neutrinos. The detection of neutrinos is therefore crucial in understanding CR acceleration in such objects. To estimate the neutrino flux, we adopt the two LHAASO sources (J2226+6057, J1908+0621) found to be spatially associated with the supernova remnants (SNR G106.3+2.7, SNR G40.5–0.5). For these two sources, the detected TeV-PeV gamma-ray spectra are found to be unusually hard (with spectral index ∼1.8). We develop a model of gamma-ray and neutrino emission based on the above two prototypes. The neutrino fluxes from these two sources are found to be below the IceCube sensitivity, but are detectable in upcoming IceCube-Gen2 and KM3NeT experiments. We further estimate the neutrino fluxes from similar other 10 LHAASO PeVatron sources and most of them are found to be detectable in IceCube-Gen2 and KM3NeT. Finally, we explore our model parameters, in particular the spectral power-law index and estimate the future potential of the neutrino detectors to probe CR acceleration in such Galactic sources.

Probing the Origin of Cosmic Rays in Cygnus Cocoon Using Ultrahigh-energy Gamma-Ray and Neutrino Observations

Recent ultrahigh-energy gamma-ray observations by the High Altitude Water Cherenkov Observatory up to 100 TeV and LHAASO observatories up to 1.4 PeV energies from the direction of Fermi Large Area Telescope 4FGL source 4FGL J2028.6 + 4110e (Cygnus Cocoon) are indicative of a hadronic origin over a leptonic process for their creation. The IceCube Neutrino Observatory has reported IceCube-201120A, a neutrino event coming from the same direction, suggesting that the Cygnus Cocoon may correspond to one of the most plausible sources of high-energy cosmic rays. The apparent relationship of the neutrino event with the observed ultrahigh-energy gamma rays from the Cygnus Cocoon is investigated in this work to study if it can be explained consistently in hadronic interactions of accelerated cosmic rays with ambient matter. Our findings reveal that leptonic mechanisms, together with pure hadronic mechanisms, make a considerable contribution to the understanding of the total electromagnetic spectrum as well as the observed neutrino event. The estimate of expected muon neutrino events from the Cygnus Cocoon agrees with the one muon neutrino event detected so far in IceCube multiyear observations. Thus, our results are indicative of the potential of the Cygnus Cocoon to be a Galactic cosmic-ray source capable of accelerating at least up to PeV energies.

Ultrahigh-energy gamma rays and gravitational waves from primordial exotic stellar bubbles

We put forward a novel class of exotic celestial objects that can be produced through phase transitions occurring in the primordial Universe. These objects appear as bubbles of stellar size and can be dominated by primordial black holes (PBHs). We report that, due to the processes of Hawking radiation and binary evolution of PBHs inside these stellar bubbles, both electromagnetic and gravitational radiations can be emitted that are featured on the gamma-ray spectra and stochastic gravitational waves (GWs). Our results reveal that, depending on the mass distribution, the exotic stellar bubbles consisting of PBHs not only provide a decent fit for the ultrahigh-energy gamma-ray spectrum reported by the recent LHAASO experiment, but also predict GW signals that are expected to be tested by the forthcoming GW surveys.

Ultra-High Energy Gamma Ray Astronomy with the Carpet Air Shower Array at the Baksan Neutrino Observatory

Ultra-High Energy Gamma Ray Astronomy with the Carpet Air Shower Array at the Baksan Neutrino Observatory

Constraining superheavy decaying dark matter with directional ultra-high energy gamma-ray limits

We present constraints on the lifetime of the superheavy decaying dark matter branching to the qq̅ channel in the mass range 1019–1025 eV based on the directional limits on the ultra-high-energy (UHE) gamma rays from dwarf spheroidal galaxies (dSphs) and the Milky Way (MW) centre obtained by the Pierre Auger Observatory and the Telescope Array experiment. Attenuation effects during the propagation of UHE photons towards Earth are taken into account. The strongest constraints are derived for the MW centre and have an order of 1020 yr. We conclude that the UHE diffuse gamma-ray limits provide more efficient signature for the superheavy DM search than the directional gamma-ray limits.

LHAASO and the origin of cosmic rays

The extension of the cosmic ray spectrum beyond 1 PeV (1 PeV = 1015 eV) indicates the existence of particle accelerators operating as PeVatrons in the Milky Way. However, recent gamma-ray observations reveal that supernova remnants (SNRs), considered the major source of galactic cosmic rays, have difficulty in accelerating cosmic rays to PeV. Therefore, searching and identifying PeVatrons is crucial for understanding the origin of cosmic rays. The ultra-high-energy (UHE) gamma-ray observations will provide decisive evidence for such studies. Due to its high sensitivity in the UHE gamma-ray band, Large High Altitude Air Shower Observatory (LHAASO) would play a key role in the research on PeVatron. After running the 1/2 LHAASO-KM2A array, 12 UHE gamma-ray sources were detected. This paper summarizes the observation results and discusses the prospect of the full LHAASO array.

Muons with threshold 1 GeV in extensive air showers with energy greater than 5 EeV

The paper presents an analysis of the characteristics of muons with a threshold greater than 1 GeV in showers with energies greater than 5 EeV and zenith angles less than 60 degrees. The analysis is based on the registration data of extensive air showers of the Yakutsk array. Estimation of muons at different distances from the shower core, fraction of muons ρμ /ρ μ+e at a distance of 600 m are obtained. Calculations of the fraction of muons are performed using the QGSjetII-04 hadronic interaction model for different primary nuclei, and compared with the data. Mass composition of primary particles is estimated by muon component. Several showers were found in the sample, with a low content of muons which possibly is produced by ultrahigh energy gamma rays.

Background identification algorithm for future self-triggered air-shower radio arrays

The study of the ultra-high energy cosmic rays, neutrinos and gamma rays is one of the most important challenges in astrophysics. The low fluxes of these particles do not allow one to detect them directly. The detection is performed by the measuring of the air-showers produced by the primary particles in the Earth's atmosphere. A radio detection of ultra-high energy air-showers is a cost-effective technique that provides a precise reconstruction of the parameters of primary particle and almost full duty cycle in comparison with other methods. The main challenge of the modern radio detectors is the development of efficient self-trigger technology, resistant to high-level background and radio frequency interference. Most of the modern radio detectors receive trigger generated by either particle or optical detectors. The development of the self trigger for the radio detector will significantly simplify the operation of existing instruments and allow one to access the main advantages of the radio method as well as open the way to the construction of the next generation of large-scale radio detectors. In the present work we discuss our progress in the solution of this problem, particularly the classification of broadband pulses.

The generation of signal and background sky maps for ultra-high energy gamma ray source with a Monte Carlo method

Studying the ultra-high energy gamma ray source is an important way to reveal the origin of the cosmic ray, which is also a main topic of many ground gamma ray experiments. To expect the observation ability during the design of the experiment, as well as to test the analyse methods in the observation, a Monte Carlo procedure for the signal and background generation is necessary. In this paper, such a procedure is introduced. And the source significance for a Blazar source Mrk421 is expected based on this procedure. Finally, an unfolding method for the source spectrum measurement is also established bashed on this Monte Carlo data, which gives fitting errors around ±10.0% both for the flux and the spectrum index.

Two Bursts of Ultra-High Energy Gamma Rays Detected by the Baksan Air Shower Array

During a Cygnus X-3 campaign many years ago the Carpet air shower array of the Baksan Neutrino Observatory had recorded two bursts from two different sources: from the Crab Nebula on February 23, 1989 and from Cygnus X-3 on October 14–16, 1985. The characteristics of the bursts were quite different, as well as types of the source objects. The first of these bursts was discussed in some detail after registration of regular flares of gamma rays with energies of several hundred MeV by the satellite gamma-ray telescopes FermiLAT and AGILE. The second burst was not discussed in recent time, and in this paper attention is attracted to it in connection with the new results of the Tibet ASγ collaboration.

The Giant Radio Array for Neutrino Detection (GRAND): Science and design

The Giant Radio Array for Neutrino Detection (GRAND) is a planned large-scale observatory of ultra-high-energy (UHE) cosmic particles, with energies exceeding 108 GeV. Its goal is to solve the long-standing mystery of the origin of UHE cosmic rays. To do this, GRAND will detect an unprecedented number of UHE cosmic rays and search for the undiscovered UHE neutrinos and gamma rays associated to them with unmatched sensitivity. GRAND will use large arrays of antennas to detect the radio emission coming from extensive air showers initiated by UHE particles in the atmosphere. Its design is modular: 20 separate, independent sub-arrays, each of 10000 radio antennas deployed over 10000 km2. A staged construction plan will validate key detection techniques while achieving important science goals early. Here we present the science goals, detection strategy, preliminary design, performance goals, and construction plans for GRAND.

The GRAND project and GRANDProto300 experiment

The Giant Array for Neutrino Detection (GRAND) is a proposal for a giant observatory of ultra-high energy cosmic particles (neutrinos, cosmic rays and gamma rays). It will be composed of twenty subarrays of 10 000 antennas each, totaling a detection area of 200 000 km2. GRAND will reach unprecedented sensitivity to neutrinos allowing to detect cosmogenic neutrinos while its sub-degree angular resolution will also make it possible to hunt for point sources and possibly start neutrino astronomy. Combined with its gigantic exposure to ultra-high energy cosmic rays and gamma rays, GRAND will be a powerful tool to solve the century-long mistery of the nature and origin of the particles with highest energy in the Universe. On the path to GRAND, the GRANDProto300 experiment will be deployed in 2020 over a total area of 200 km2. It primarly aims at validating the detection concept of GRAND, but also proposes a rich science program centered on a precise and complete measurement of the air showers initiated by cosmic rays with energies between 1016.5and 1018eV, a range where we expect to observe the transition between the Galactic and extra-galactic origin of cosmic rays.

Radio detection in the multi-messenger context

The present work discusses the development of the radio technique for detection of ultra-high energy air-showers induced by cosmic radiation, and the prospects of its application in the future multi-messenger activities, particularly for detection of ultra-high energy cosmic rays, gamma rays and neutrinos. It gives an overview of the results achieved by the modern digital radio arrays, as well as discuss present challenges and future prospects.

Recent results from the KASCADE-Grande data analysis

KASCADE, together with its extension KASCADE-Grande measured individual air showers of cosmic rays in the primary energy range of 100 TeV to 1 EeV. The data collection was fully completed at the end of 2013 and the experiment was dismantled. However, the data analysis is still in progress. Recently, we published a new result on upper limits to the flux of ultra-high energy gamma rays, which set constraints on some fundamental astrophysical models. We also use the data to investigate the validity of the new hadronic interactions models like SIBYLL version 2.3c or EPOS-LHC. In addition, we updated and improved the webbased platform of the KASCADE Cosmic Ray Data Centre (KCDC), where now the data from KASCADE and KASCADE-Grande of more than 20 years measurements is available, including corresponding Monte-Carlo simulated events based on three different hadronic interaction models. In this contribution, recent results from KASCADE-Grande and the update of KCDC is briefly discussed.

On the origin of the TeV gamma-ray emission from Cygnus X-3

Cygnus X-3 binary system is a famous object studied over the wide range of electromagnetic spectrum. Early detections of ultra-high energy gamma-rays from Cygnus X-3 by Kiel, Havera Park and then by Akeno triggered the construction of several large air shower detectors. Also, Cygnus X-3 has been proposed to be one of the most powerful sources of charged cosmic ray particles in the Galaxy. The results of twenty-year observations of the Cyg X-3 binary at energies 800 GeV - 85 TeV are presented with images, spectra during periods of flaring activity and at low flux periods. The correlation of TeV flux increases with flaring activity at the lower energy range of X-ray and radio emission from the relativistic jets of Cygnus X-3 is found as well as 4.8-hour orbital modulation of TeV γ-ray intensity. Detected modulation of TeV γ-ray emission with orbit and important characteristics of Cyg X-3 such as the high luminosity of the companion star and the close orbit leads to an efficient generation of γ-ray emission through inverse Compton scattering in this object. The different type variability of very high-energy γ-emission and correlation of radiation activity in the wide energy range can provide essential information on the mechanism of particle production up to very high energies.