scholarly journals NEW RESULTS FROM H.E.S.S. OBSERVATIONS OF GALAXY CLUSTERS

2009 ◽  
Vol 18 (10) ◽  
pp. 1627-1631 ◽  
Author(s):  
◽  
WILFRIED DOMAINKO ◽  
DALIBOR NEDBAL ◽  
JAMES A. HINTON ◽  
OLIVIER MARTINEAU-HUYNH
Keyword(s):  
Cosmic Rays ◽  
Galaxy Clusters ◽  
Gamma Rays ◽  
Large Scale ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Clusters Of Galaxies ◽  
X Ray ◽  
Model Predictions ◽  
The Universe

Clusters of galaxies are believed to contain a significant population of cosmic rays. From the radio and probably hard X-ray bands it is known that clusters are the spatially most extended emitters of non-thermal radiation in the Universe. Due to their content of cosmic rays, galaxy clusters are also potential sources of VHE (> 100 GeV) gamma rays. Recently, the massive, nearby cluster Abell 85 has been observed with the H.E.S.S. experiment in VHE gamma rays with a very deep exposure as part of an ongoing campaign. No significant gamma-ray signal has been found at the position of the cluster. The non-detection of this object with H.E.S.S. constrains the total energy of cosmic rays in this system. For a hard spectral index of the cosmic rays of -2.1 and if the cosmic-ray energy density follows the large scale gas density profile, the limit on the fraction of energy in these non-thermal particles with respect to the total thermal energy of the intra-cluster medium is 8% for this particular cluster. This value is at the lower bounds of model predictions.

COSMOLOGICAL SHOCK WAVES IN THE LARGE SCALE STRUCTURE OF THE UNIVERSE

2013 ◽  
Vol 23 ◽  
pp. 386-390
Author(s):  
RENYI MA ◽  
DONGSU RYU ◽  
HYESUNG KANG
Keyword(s):  
Shock Waves ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Gamma Ray ◽  
High Redshift ◽  
Cosmic Ray ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Weak Shocks ◽  
The Universe

Based on the cosmological hydrodynamic simulation, we study the properties of shock waves formed during the formation of the large scale structure (LSS) of the universe, and investigate their contribution to the cosmic ray (CR) fraction in the intergalactic medium (IGM). It is found that while strong accretion shocks prevail at high redshift, weak internal shocks become dominant in the intracluster medium (ICM) as galaxy clusters form and virialize at low redshift, z < 1. The accumulated CR proton energy is likely to be less than 10 % of the thermal energy in the ICM, since weak shocks of M ≲ 3 are most abundant. This is consistent with the upper limit constrained by radio and gamma-ray observations of galaxy clusters. In the warm-hot medium (WHIM) inside filaments, CRs and gas could be almost in energy equipartition, since relatively stronger shocks of 5 ≲ M ≲ 10 are dominant there. We suggest that the non-thermal emissions from the CR electrons and protons accelerated by cosmological shock waves could provide a new way to detect the WHIM of the universe.

scholarly journals Modeling Gamma-Ray SEDs and Angular Extensions of Extreme TeV Blazars from Intergalactic Proton-Initiated Cascades in Contemporary Astrophysical EGMF Models

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 220
Author(s):  
Emil Khalikov
Keyword(s):  
Gamma Rays ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
Cascade Model ◽  
Point Sources ◽  
Spectral Energy ◽  
Observation Data ◽  
Cherenkov Telescopes ◽  
The Universe

The intrinsic spectra of some distant blazars known as “extreme TeV blazars” have shown a hint at an anomalous hardening in the TeV energy region. Several extragalactic propagation models have been proposed to explain this possible excess transparency of the Universe to gamma-rays starting from a model which assumes the existence of so-called axion-like particles (ALPs) and the new process of gamma-ALP oscillations. Alternative models suppose that some of the observable gamma-rays are produced in the intergalactic cascades. This work focuses on investigating the spectral and angular features of one of the cascade models, the Intergalactic Hadronic Cascade Model (IHCM) in the contemporary astrophysical models of Extragalactic Magnetic Field (EGMF). For IHCM, EGMF largely determines the deflection of primary cosmic rays and electrons of intergalactic cascades and, thus, is of vital importance. Contemporary Hackstein models are considered in this paper and compared to the model of Dolag. The models assumed are based on simulations of the local part of large-scale structure of the Universe and differ in the assumptions for the seed field. This work provides spectral energy distributions (SEDs) and angular extensions of two extreme TeV blazars, 1ES 0229+200 and 1ES 0414+009. It is demonstrated that observable SEDs inside a typical point spread function of imaging atmospheric Cherenkov telescopes (IACTs) for IHCM would exhibit a characteristic high-energy attenuation compared to the ones obtained in hadronic models that do not consider EGMF, which makes it possible to distinguish among these models. At the same time, the spectra for IHCM models would have longer high energy tails than some available spectra for the ALP models and the universal spectra for the Electromagnetic Cascade Model (ECM). The analysis of the IHCM observable angular extensions shows that the sources would likely be identified by most IACTs not as point sources but rather as extended ones. These spectra could later be compared with future observation data of such instruments as Cherenkov Telescope Array (CTA) and LHAASO.

scholarly journals Interaction between molecular clouds and MeV–TeV cosmic-ray protons escaped from supernova remnants

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Ken Makino ◽  
Yutaka Fujita ◽  
Kumiko K Nobukawa ◽  
Hironori Matsumoto ◽  
Yutaka Ohira
Keyword(s):  
Gamma Rays ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Iron Line ◽  
X Ray ◽  
Line Intensities ◽  
Neutral Gas ◽  
Additional Support

Abstract Recent discovery of the X-ray neutral iron line (Fe  i Kα at 6.40 keV) around several supernova remnants (SNRs) show that MeV cosmic-ray (CR) protons are distributed around the SNRs and are interacting with neutral gas there. We propose that these MeV CRs are the ones that have been accelerated at the SNRs together with GeV–TeV CRs. In our analytical model, the MeV CRs are still confined in the SNR when the SNR collides with molecular clouds. After the collision, the MeV CRs leak into the clouds and produce the neutral iron line emissions. On the other hand, GeV–TeV CRs had already escaped from the SNRs and emitted gamma-rays through interaction with molecular clouds surrounding the SNRs. We apply this model to the SNRs W 28 and W 44 and show that it can reproduce the observations of the iron line intensities and the gamma-ray spectra. This could be additional support of the hadronic scenario for the gamma-ray emissions from these SNRs.

scholarly journals On the flux of high-energy cosmogenic neutrinos and the influence of the extragalactic magnetic field

2019 ◽  
Vol 488 (1) ◽  
pp. L119-L122 ◽  
Author(s):  
David Wittkowski ◽  
Karl-Heinz Kampert
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Large Scale ◽  
Neutrino Flux ◽  
Cosmic Ray ◽  
High Energy ◽  
Observation Time ◽  
Cosmological Time ◽  
Cosmic Background ◽  
The Universe

ABSTRACT Cosmogenic neutrinos originate from interactions of cosmic rays propagating through the universe with cosmic background photons. Since both high-energy cosmic rays and cosmic background photons exist, the existence of high-energy cosmogenic neutrinos is certain. However, their flux has not been measured so far. Therefore, we calculated the flux of high-energy cosmogenic neutrinos arriving at the Earth on the basis of elaborate 4D simulations that take into account three spatial degrees of freedom and the cosmological time-evolution of the universe. Our predictions for this neutrino flux are consistent with the recent upper limits obtained from large-scale cosmic-ray experiments. We also show that the extragalactic magnetic field has a strong influence on the neutrino flux. The results of this work are important for the design of future neutrino observatories, since they allow to assess the detector volume and observation time that are necessary to detect high-energy cosmogenic neutrinos in the near future. An observation of such neutrinos would push multimessenger astronomy to hitherto unachieved energy scales.

scholarly journals Interpreting correlated observations of cosmic rays and gamma-rays from Centaurus A with a proton blazar inspired model

2020 ◽  
Vol 500 (1) ◽  
pp. 1087-1094
Author(s):  
Prabir Banik ◽  
Arunava Bhadra ◽  
Abhijit Bhattacharyya
Keyword(s):  
Cosmic Rays ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Energy Scale ◽  
Electromagnetic Spectrum ◽  
Ultrahigh Energy ◽  
Large Area ◽  
Centaurus A

ABSTRACT The nearest active radio galaxy Centaurus (Cen) A is a gamma-ray emitter in GeV–TeV energy scale. The high energy stereoscopic system (HESS) and non-simultaneous Fermi–Large Area Telescope observation indicate an unusual spectral hardening above few GeV energies in the gamma-ray spectrum of Cen A. Very recently the HESS observatory resolved the kilo parsec (kpc)-scale jets in Centaurus A at TeV energies. On the other hand, the Pierre Auger Observatory (PAO) detects a few ultrahigh energy cosmic ray (UHECR) events from Cen-A. The proton blazar inspired model, which considers acceleration of both electrons and hadronic cosmic rays in active galactic nuclei (AGN) jet, can explain the observed coincident high-energy neutrinos and gamma-rays from Ice-cube detected AGN jets. Here, we have employed the proton blazar inspired model to explain the observed GeV–TeV gamma-ray spectrum features including the spectrum hardening at GeV energies along with the PAO observation on cosmic rays from Cen-A. Our findings suggest that the model can explain consistently the observed electromagnetic spectrum in combination with the appropriate number of UHECRs from Cen A.

scholarly journals IMPLICATIONS OF PC AND KPC JET ASYMMETRY TO THE COSMIC RAY ACCELERATION

2012 ◽  
Vol 08 ◽  
pp. 331-335
Author(s):  
NECTARIA A. B. GIZANI
Keyword(s):  
Cosmic Rays ◽  
Active Galactic Nuclei ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Cosmic Ray ◽  
Directional Asymmetry ◽  
X Ray ◽  
Radio Data ◽  
High Energies ◽  
Cosmic Ray Acceleration

We probe the role that the directional asymmetry, between relativistic outflows and kilo-parsec scale jets, play in the acceleration of cosmic rays. For this reason we use two powerful, nearby Active Galactic Nuclei (AGNs). These radio galaxies are atypical compared to the usual AGN as they contain ring-like features instead of hotspots. Our VLBI radio data have revealed a substantial misalignment between their small and large scale jets. Taking into account the overall information we have obtained about the AGNs themselves (VLA and VLBI radio data at 18 cm) and their clusters (X-ray observations) our study supports the present ideas of powerful radiogalaxies (radio quiet and radio loud) being sources of cosmic rays as well as their ability to accelarate the latter to ultra high energies.

scholarly journals The X-Ray Background: Origin and Implications

1980 ◽  
Vol 92 ◽  
pp. 207-225
Author(s):  
Martin J. Rees
Keyword(s):  
Large Scale ◽  
Clusters Of Galaxies ◽  
X Ray ◽  
X Ray Background ◽  
The Universe

This paper will be concerned with three topics relevant to the X-ray background: (i) X-ray emission mechanisms in quasars; (ii) the contributions to the X-ray background from quasars, clusters of galaxies, intercluster gas, young galaxies, etc; and (iii) the use of X-ray background observations as a probe for large-scale density irregularities in the Universe.

scholarly journals Gamma-rays from reaccelerated particles at supernova remnant shocks

2019 ◽  
Vol 489 (1) ◽  
pp. 108-115 ◽  
Author(s):  
P Cristofari ◽  
P Blasi
Keyword(s):  
Gamma Rays ◽  
Supernova Remnants ◽  
Large Scale ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
X Rays ◽  
Diffusive Shock Acceleration ◽  
Particle In Cell ◽  
Large Scale Magnetic Field

ABSTRACT Diffusive shock acceleration is considered as the main mechanism for particle energization in supernova remnants, as well as in other classes of sources. The existence of some remnants that show a bilateral morphology in the X-rays and gamma-rays suggests that this process occurs with an efficiency that depends upon the inclination angle between the shock normal and the large-scale magnetic field in which the shock propagates. This interpretation is additionally supported by recent particle-in-cell simulations that show how ions are not injected if the shock is more oblique than ∼45°. These shocks provide an excellent test bench for the process of reacceleration at the same shock: non-thermal seed particles that are reached by the shock front are automatically injected and accelerated. This process was recently discussed as a possible reason for some anomalous behaviour of the spectra of secondary cosmic ray nuclei. Here, we discuss how gamma-ray observations of selected supernova remnants can provide us with precious information about this process and lead us to a better assessment of particle diffusive shock reacceleration for other observables in cosmic ray physics.

scholarly journals ULTRA HIGH ENERGY COSMIC RAYS: ORIGIN AND PROPAGATION

2010 ◽  
Vol 25 (18) ◽  
pp. 1467-1481 ◽  
Author(s):  
TODOR STANEV
Keyword(s):  
Cosmic Rays ◽  
Gamma Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Ultra High Energy ◽  
Ultrahigh Energy ◽  
High Energy Cosmic Rays ◽  
Astrophysical Objects ◽  
Ultrahigh Energy Cosmic Rays ◽  
The Universe

We introduce the highest energy cosmic rays and briefly review the powerful astrophysical objects where they could be accelerated. We then introduce the interactions of different cosmic ray particles with the photon fields of the Universe and the formation of the cosmic ray spectra observed at Earth. The last topic is the production of secondary gamma rays and neutrinos in the interactions of the ultrahigh energy cosmic rays.

scholarly journals Limiting the shock acceleration of cosmic ray protons in the ICM

2020 ◽  
Vol 495 (1) ◽  
pp. L112-L117 ◽  
Author(s):  
D Wittor ◽  
F Vazza ◽  
D Ryu ◽  
H Kang
Keyword(s):  
Cosmic Rays ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Magnetic Field Topology ◽  
Tracer Particles ◽  
Γ Rays ◽  
Massive Galaxy

ABSTRACT Observations of large-scale radio emissions prove the existence of shock accelerated cosmic ray electrons in galaxy clusters, while the lack of detected γ-rays limits the acceleration of cosmic ray protons in galaxy clusters. This challenges our understanding of how diffusive shock acceleration works. In this work, we couple the most updated recipes for shock acceleration in the intracluster medium to state-of-the-art magnetohydrodynamical simulations of massive galaxy clusters. Furthermore, we use passive tracer particles to follow the evolution of accelerated cosmic rays. We show that when the interplay between magnetic field topology and the feedback from accelerated cosmic rays is taken into account, the latest developments of particle acceleration theory give results that are compatible with observational constraints.

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