High Energy Gamma-ray Research Articles

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.

The Gravitational-wave Optical Transient Observer (GOTO): prototype performance and prospects for transient science

ABSTRACT The Gravitational-wave Optical Transient Observer (GOTO) is an array of wide-field optical telescopes, designed to exploit new discoveries from the next generation of gravitational wave detectors (LIGO, Virgo, and KAGRA), study rapidly evolving transients, and exploit multimessenger opportunities arising from neutrino and very high energy gamma-ray triggers. In addition to a rapid response mode, the array will also perform a sensitive, all-sky transient survey with few day cadence. The facility features a novel, modular design with multiple 40-cm wide-field reflectors on a single mount. In 2017 June, the GOTO collaboration deployed the initial project prototype, with 4 telescope units, at the Roque de los Muchachos Observatory (ORM), La Palma, Canary Islands. Here, we describe the deployment, commissioning, and performance of the prototype hardware, and discuss the impact of these findings on the final GOTO design. We also offer an initial assessment of the science prospects for the full GOTO facility that employs 32 telescope units across two sites.

Chapter 6 Multimessenger Physics * *Supported by the Natural Science Foundation of China (11773003, 11875264, 12003007, 12173091, U1931201, U2031105), and the Fundamental Research Funds for the Central Universities (2020kfyXJJS039)

Combining observations of multi-messengers help in boosting the sensitivity of astrophysical source searches, and probe various aspects of the source physics. In this chapter we discuss how LHAASO observations of very high energy (VHE) gamma rays in combination with telescopes for the other messengers can help in solving the origins of VHE neutrinos and galactic and extragalactic cosmic rays.

Gamma-Ray Bursts at TeV Energies: Observational Status

Gamma-ray bursts (GRBs) are some of the most energetic events in the Universe and are potential sites of cosmic ray acceleration up to the highest energies. GRBs have therefore been a target of interest for very high energy gamma-ray observatories for many years, leading to the recent discovery of a number of bursts with photons reaching energies above 100 GeV. We summarize the GRB observational campaigns of the current generation of very high energy gamma-ray observatories as well as describing the observations and properties of the GRBs discovered so far. We compare the properties of the very high energy bursts to the total GRB distribution and make predictions for the next generation of very high energy gamma-ray observations.

Galactic and extragalactic sources of very high energy gamma rays

Very high energy $$\gamma $$ -rays are one of the most important messengers of the relativistic non-thermal Universe. The major motivation of very high energy $$\gamma $$ -ray astronomy is to find sources of high energy cosmic rays. Several astrophysical sources are known to accelerate cosmic rays to very high energies under extreme conditions. Very high energy $$\gamma $$ -rays are produced at these astrophysical sites or in their vicinity through interactions of cosmic rays in the surrounding medium close to the sources. Gamma rays, being neutral, travel in a straight line and thus give us valuable information about the cosmic ray sources and their surroundings. Additionally, very high energy $$\gamma $$ -ray astronomy can probe many fundamental physics questions. Ground-based $$\gamma $$ -ray astronomy began its journey in 1989 when Whipple telescope detected TeV $$\gamma $$ -rays from the Crab, a pulsar wind nebula in our galaxy. In the last 2 decades, technological improvements have facilitated the development of the latest generation of very high energy detectors and telescopes which have delivered exciting new results. Until now, over two hundred very high energy $$\gamma $$ -ray sources, both galactic and extra-galactic, have been detected. These observations have provided a deeper insight into a large number of important questions in high energy astrophysics and astroparticle physics. This review article is an attempt to enumerate the most important results in the exciting and rapidly developing field of very high energy $$\gamma $$ -ray astronomy.

Cosmic Ray production in SNRs of Pulsar Wind Nebulae type at different ages

The overall observations of plerions from radio to the very high energy gamma-rays could provide information about the evolution of PWN from the young Crab-like to the older stages. The extended MeV-TeV emission from Geminga middle-aged pulsar of ~ 3.4 × 105year age in SHALON, Milagro, HAWC observations, and Fermi-LAT detection could arise from the PWN associated with the Geminga SNR. The TeVγ-ray emission from 3C 58 PWN whose estimated age varies from ~ 800 to (5 − 7) × 103years was first detected in year 2011 by SHALON. The overall spectral energy distribution and information about the extension of PWN from radio to GeV-TeV energies from Fermi-LAT and SHALON observations can contribute to particle transport models and also to the understanding of the mechanisms of PWN expanding, which is, in turn, can shed light on the age of 3C 58 and the history of progenitor SN explosion.

The observation of high-energy neutrinos from the cosmos: Lessons learned for multimessenger astronomy

The IceCube neutrino telescope discovered PeV-energy neutrinos originating beyond our Galaxy with an energy flux that is comparable to that of GeV-energy gamma rays and EeV-energy cosmic rays. These neutrinos provide the only unobstructed view of the cosmic accelerators that power the highest energy radiation reaching us from the universe. We will review the results from IceCube’s first decade of operations, emphasizing the measurement of the diffuse multiflavored neutrino flux from the universe and the identification of the supermassive black hole TXS [Formula: see text] as a source of cosmic neutrinos and, therefore, cosmic rays. We will speculate on the lessons learned for multimessenger astronomy, among them that extragalactic neutrino sources may be a relatively small subset of the cosmic accelerators observed in high-energy gamma rays and that these may be gamma-ray-obscured at the times that they emit neutrinos.

Activity standardization by means of liquid scintillation counting and determination of the half-life of 89Zr

A89Zr solution was measured by means of liquid scintillation counting techniques in order to determine the activity concentration. Two methods were used: the CIEMAT/NIST efficiency tracing method with 3H as a tracer, and the triple-to-double coincidence ratio method. The counting efficiencies were computed with a stochastic model. The very detailed investigation showed that a few corrections are particularly important: Asymmetries in the photodetector responses as well as the backscattering of high-energy gamma rays must be taken into account. Corresponding corrections have therefore been applied. In addition, a detailed uncertainty analysis was carried out and the uncertainties compared with those determined by other research groups.The activity concentrations obtained from the two methods agree well and a combined result was used to establish calibration factors for ionization chambers, which are important secondary standardization instruments. The ionization chambers were combined with a new high-precision current measurement device to provide outstanding linearity. Measurement data from one chamber were used to determine the half-life, which was found to be T1/2=(78.373 ± 0.023) h.

Sir Arnold Whittaker Wolfendale. 25 June 1927—21 December 2020

For over 50 years Arnold Wolfendale was an international leader in the fields of cosmic ray and gamma ray astronomy, making many seminal contributions. His extensive studies of the muon particle culminated in 1965 when, using an installation in the Kolar Gold Mine in India, he played a major role in the first detection of the neutrinos associated with muons produced in the atmosphere. His interests in the origin of high-energy cosmic rays were extensive and required the development of a better understanding of particle physics at energies beyond those accessible at accelerators. Recognizing that high-energy gamma rays can arise from cosmic ray interactions with the interstellar gas, he used early satellite data to argue for the galactic origin of intermediate-energy cosmic rays and for studies of the distribution of molecular hydrogen. His interests in astronomy, which he firmly held to be a branch of physics, drove him to develop a world-class activity in this area at Durham University. This achievement, in part, led to him being appointed Astronomer Royal in 1991. He used this position, and his roles as president of the Royal Astronomical Society, the Institute of Physics and the European Physical Society, to lobby tirelessly for more governmental support for science. He was an early advocate for improvements in the public understanding of science, leading by example. In his later years Arnold's interests extended to cosmology and horology, and he argued against a possible connection between cosmic rays and global warming. A brilliant communicator, Arnold gave a huge number of lectures each year to general audiences, almost to the end of his life.

Probing the Dark Matter of the Three-loop Radiative Neutrino Mass Generation Model with the Cherenkov Telescope Array

We investigate the prospect of detecting the Dark Matter (DM) candidate in the three-loop radiative neutrino mass generation model extended with large electroweak multiplets of the Standard Model (SM) gauge group, at the future imaging atmospheric Cherenkov telescope known as the Cherenkov Telescope Array (CTA). We find that the addition of such large electroweak multiplets leads to a sizable Sommerfeld enhanced annihilation of the DM with O(TeV) mass, into the SM gauge bosons which results in continuum and line-like spectra of very high energy (VHE) gamma-rays, and therefore becomes observable for the CTA. By considering the continuum VHE gamma-rays produced from the DM annihilation at the Galactic center, we probe the parameter space of the model using the sensitivity reach of the CTA.

The spectral energy distribution of an X-ray pair halo from a gamma-ray source with a power-law continuum

Interactions between Very High Energy (VHE) gamma-rays from Active Galactic Nuclei (AGNs) and infrared photons from the Extragalactic Background Light (EBL) can start electromagnetic cascades. If the extragalactic magnetic field near a host galaxy is strong enough (∼1 µG), the cascades would develop isotropically around the AGN. As a result, the electron/positron pairs created along the development of the cascades would create an X-ray halo via synchrotron radiation process. It is believed that the VHE gamma-ray spectra from the AGNs could be approximated by a power-law model which is truncated at high energy end (i.e. maximum energy). In this work we studied the X-ray Spectral Energy Distribution (SED) of the halo generated from the AGN spectra with different power indices and maximum energy levels. The results showed that the SEDs were slightly higher and broader, as they were obtaining higher flux if the power indices were lower. On the other hand, the SEDs were sensitive to the maximum energy levels between 100-300 TeV. More flux could be obtained from the higher maximum energy. However, we found that the SED becomes insensitive to the varied parameters when the maximum energy and the power index are > 500 TeV and < 1.5, respectively.

The Crab Pulsar and Nebula as Seen in Gamma-Rays

Slightly more than 30 years ago, Whipple detection of the Crab Nebula was the start of Very High Energy gamma-ray astronomy. Since then, gamma-ray observations of this source have continued to provide new surprises and challenges to theories, with the detection of fast variability, pulsed emission up to unexpectedly high energy, and the very recent detection of photons with energy exceeding 1 PeV. In this article, we review the impact of gamma-ray observations on our understanding of this extraordinary accelerator.

Reconciling hints on axion-like-particles from high-energy gamma rays with stellar bounds

It has been recently claimed by two different groups that the spectral modulation observed in gamma raysfrom Galactic pulsars and supernova remnants can be due to conversion of photons into ultra-light axion-like-particles (ALPs) in large-scale Galactic magnetic fields.While we show the required best-fit photon-ALP coupling, gaγ ∼ 2 × 10-10 GeV-1, to be consistent with constraints from observations of photon-ALPs mixing in vacuum, this is in conflict with other bounds, specifically from the CAST solar axion limit, from the helium-burning lifetime in globular clusters, and from the non-observations of gamma rays in coincidencewith SN 1987A. In order to reconcile these different results, we propose that environmental effects in matter would suppress the ALP production in dense astrophysical plasma, allowing to relax previous bounds and make them compatible with photon-ALP conversions in the low-density Galactic medium. If this explanation is correct, the claimed ALP signal would be on the reach of next-generations laboratory experiments such as ALPS II.

Long-term multi-band photometric monitoring of Mrk 501

Aims. Radio-to-TeV observations of the bright nearby (z = 0.034) blazar Markarian 501 (Mrk 501), performed from December 2012 to April 2018, are used to study the emission mechanisms in its relativistic jet. Methods. We examined the multi-wavelength variability and the correlations of the light curves obtained by eight different instruments, including the First G-APD Cherenkov Telescope (FACT), observing Mrk 501 in very high-energy (VHE) gamma-rays at TeV energies. We identified individual TeV and X-ray flares and found a sub-day lag between variability in these two bands. Results. Simultaneous TeV and X-ray variations with almost zero lag are consistent with synchrotron self-Compton (SSC) emission, where TeV photons are produced through inverse Compton scattering. The characteristic time interval of 5−25 days between TeV flares is consistent with them being driven by Lense-Thirring precession.

High-energy gamma-rays and neutrons observed in very impulsive solar flare on 2012 June 3

AbstractAn impulsive solar flare was observed on 2012 June 3 by the Geostationary Operational Environment Satellite. In this flare, a salient feature was recognized whereby high-energy ions were accelerated to a few GeV within one minute. Associated with this flare, high-energy gamma-rays as well as high-energy neutrons were detected by the Space Environment Data Acquisition equipment onboard the International Space Station. A remarkable feature found of this event was an exceedingly high n$/$γ-ratio observed between the intensities of high-energy neutrons and gamma-rays. To understand a high n$/$γ-ratio of about 600, the interaction processes between the accelerated ions and ambient solar atmosphere were simulated for various test cases, taking into account the magnetic field of the photosphere. The simulation was extended by using the GEANT4 code and it was shown that the observed results could be reproduced under certain conditions selected for the actual interaction process. The results suggest that helium and C, N, and O ions were predominantly accelerated in this flare, and that high-energy gamma-rays and neutrons were produced by interactions between the accelerated ions and the ambient gas. As a result, a high n$/$γ-ratio was produced.

High-energy gamma-ray emission from SNR G57.2+0.8 hosting SGR J1935+2154

In recent years some efforts have been made to identify active sources capable of accelerating particles up to 1015 eV, known as PeVatrons. Measurements of TeV (1012 eV) gamma-rays from supernova remnants (SNRs) have shown that efficient particle acceleration can occur in SNR diffusive shocks. In this paper, we obtain the contribution to the high energy and very high-energy gamma-ray (VHE, E > 100 GeV) emission due to cosmic-ray acceleration from SNR G57.2+0.8 hosting the Soft Gamma Repeater (SGR) J1935+2154 with the use of the GALPROP code. To do so, we take into account the SNR + SGR association as a single source close to the Galactic center.We propose that the above setting can provide a more comprehensive scenario for the generation of GeV-TeV gamma-rays. We also discuss the contribution from the SNR G57.2+0.8 and SGR J1935+2154 region to the diffusive TeV energy gamma-ray emission from the Galactic center.

Could Nearby Star-forming Galaxies Light Up the Pointlike Neutrino Sky?

Abstract Star-forming and starburst galaxies, which are well-known cosmic-ray reservoirs, are expected to emit gamma-rays and neutrinos predominantly via hadronic collisions. In this Letter, we analyze the 10 yr Fermi-LAT spectral energy distributions of 13 nearby galaxies by means of a physical model which accounts for high-energy proton transport in starburst nuclei and includes the contribution of primary and secondary electrons. In particular, we test the hypothesis that the observed gamma-ray fluxes are mostly due to star-forming activity, in agreement with the available star formation rates coming from IR and UV observations. Through this observation-based approach, we determine the most likely neutrino counterpart from star-forming and starburst galaxies and quantitatively assess the ability of current and upcoming neutrino telescopes to detect them as pointlike sources. Remarkably, we find that the cores of the Small Magellanic Cloud and the Circinus galaxy are potentially observable by KM3NeT/ARCA with 6 yr of observation. Moreover, most of the nearby galaxies are likely to be just a factor of a few below the KM3NeT and IceCube-Gen2 pointlike sensitivities. After investigating the prospects for detection of gamma-rays above TeV energies from these sources, we conclude that the joint observations of high-energy neutrinos and gamma-rays with upcoming telescopes will be an objective test for our emission model and may provide compelling evidence of star-forming activity as a tracer of neutrino production.

Searching for TeV Gamma-Ray Emission from SGR 1935+2154 during Its 2020 X-Ray and Radio Bursting Phase

Abstract Magnetar hyperflares are the most plausible explanation for fast radio bursts (FRBs)—enigmatic powerful radio pulses with durations of several milliseconds and high brightness temperatures. The first observational evidence for this scenario was obtained in 2020 April when an FRB was detected from the direction of the Galactic magnetar and soft gamma-ray repeater SGR 1935+2154. The FRB was preceded by two gamma-ray outburst alerts by the BAT instrument aboard the Swift satellite, which triggered follow-up observations by the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observed SGR 1935+2154 for 2 hr on 2020 April 28. The observations are coincident with X-ray bursts from the magnetar detected by INTEGRAL and Fermi-GBM, thus providing the first very high energy gamma-ray observations of a magnetar in a flaring state. High-quality data acquired during these follow-up observations allow us to perform a search for short-time transients. No significant signal at energies E &gt; 0.6 TeV is found, and upper limits on the persistent and transient emission are derived. We here present the analysis of these observations and discuss the obtained results and prospects of the H.E.S.S. follow-up program for soft gamma-ray repeaters.

Simulations of Neutrino and Gamma-Ray Production from Relativistic Black-Hole Microquasar Jets

Recently, microquasar jets have aroused the interest of many researchers focusing on the astrophysical plasma outflows and various jet ejections. In this work, we concentrate on the investigation of electromagnetic radiation and particle emissions from the jets of stellar black hole binary systems characterized by the hadronic content in their jets. Such emissions are reliably described within the context of relativistic magneto-hydrodynamics. Our model calculations are based on the Fermi acceleration mechanism through which the primary particles (mainly protons and electrons) of the jet are accelerated. As a result, a small portion of thermal protons of the jet acquire relativistic energies, through shock-waves generated into the jet plasma. From the inelastic collisions of fast (non-thermal) protons with the thermal (cold) ones, secondary charged and neutral particles (pions, kaons, muons, η-particles, etc.) are created, as well as electromagnetic radiation from the radio wavelength band to X-rays and even very high energy gamma-rays. One of our main goals is, through the appropriate solution of the transport equation and taking into account the various mechanisms that cause energy losses to the particles, to study the secondary particle concentrations within hadronic astrophysical jets. After assessing the suitability and sensitivity of the derived (for this purpose) algorithms on the Galactic MQs SS 433 and Cyg X-1, as a concrete extragalactic binary system, we examine the LMC X-1 located in the Large Magellanic Cloud, a satellite galaxy of our Milky Way Galaxy. It is worth mentioning that, for the companion O star (and its extended nebula structure) of the LMC X-1 system, new observations using spectroscopic data from VLT/UVES have been published a few years ago.

Constraining the contribution of Gamma-Ray Bursts to the high-energy diffuse neutrino flux with 10 years of ANTARES data

Gamma-Ray Bursts (GRBs) are considered very interesting astrophysical sources to be studied in the context of neutrino astronomy. Indeed, their jet composition continues to be an open issue. Within the framework of the fireball model, mesons can be produced during photo-hadronic interactions occurring in the internal shocks between shells emitted by the central engine. From their decays, high-energy gamma rays and neutrinos are expected to be generated. Neutrino telescopes are particularly interested in GRBs: being the most powerful explosions observable in the Universe, they are potentially able to achieve the energetics required to contribute to the diffuse astrophysical neutrino flux measured few years ago by IceCube. The analysis here presented relies on the search of time and space coincidences between neutrinos and the GRB emission. The undersea neutrino telescope ANTARES, operational in the Northern hemisphere since 2008 in its full configuration, plays an important role in the cosmic neutrino searches. In this contribution, the results of a stacked search for astrophysical muon neutrinos are presented for 784 GRBs in the period 2007-2017 using the ANTARES data. Given the absence of coincidences between a neutrino and a GRB in the considered sample, this analysis has allowed to constrain the contribution of the detected GRB population to the neutrino diffuse flux to be less than 10% around 100 TeV, within the context of the internal shock model. In addition, for the first time in this kind of analysis, the uncertainties on the not well characterised GRB parameters, needed to compute the neutrino flux expectations, are taken into account for each individual burst and then propagated to the diffuse flux from GRBs and to the estimated stacked upper limit.