TeV Γ-ray Emission Research Articles

Study on the spectrum of the injected relativistic protons

AbstractAbout 10 TeV γ-ray emission within 10 pc region from the Galactic Center had been reported by 4 independent groups. Considering that this TeV γ-ray emission is produced via a hadronic model, and the relativistic protons came from the tidal disruption of stars by massive black holes, we investigate the spectral nature of the injected relativistic protons required by the hadronic model. The calculation was carried on the tidal disruption of the different types of stars and the different propagation mechanisms of protons in the interstellar medium. Compared with the observation data from HESS, we find for the best fitting that the power-law index of the spectrum of the injected protons is about −1.9, when a red giant star is tidally disrupted, and the effective confinement of protons diffusion mechanism is adopted.

-ray production in young open clusters: Berk 87, Cyg OB2 and Westerlund 2

Young open clusters are sites of cosmic ray acceleration as indicated by recent detections of the TeV γ-ray sources in the directions of two open clusters (Cyg OB2 and Westerlund 2). In fact, up to now a few different scenarios for acceleration of particles inside open clusters have been considered, i.e. shocks in massive star winds, pulsars and their nebulae, supernova shocks, massive compact binaries. Here we consider in detail the radiation processes due to both electrons and hadrons accelerated inside the open cluster. As a specific scenario, we apply the acceleration process at the shocks arising in the winds of Wolf–Rayet (WR) type stars. Particles diffuse through the medium of the open cluster during the activity time of the acceleration scenario defined by the age of the WR star. They interact with the matter and radiation, at first inside the open cluster and, later in the dense surrounding clouds. We calculate the broad-band spectrum in different processes for three exemplary open clusters (Berk 87, Cyg OB2, Westerlund 2) for which the best observational constraints on the spectra are at present available. It is assumed that the high-energy phenomena, observed from the X-ray up to the GeV–TeV γ-ray energies, are related to each other. We conclude that the most likely description of the radiation processes in these objects is achieved in the hybrid (leptonic–hadronic) model in which leptons are responsible for the observed X-ray and GeV γ-ray emission and hadrons are responsible for the TeV γ-ray emission.

Production of TeV Gamma Radiation in the Vicinity of the Supermassive Black Hole in the Giant Radio Galaxy M87

Although the giant radio galaxy M87 harbors many distinct regions of broadband nonthermal emission, the recently reported fast variability of TeV γ-rays from M87, on a timescale of days, strongly constrains the range of speculations concerning the possible sites and scenarios of particle acceleration responsible for the observed TeV emission. A natural production site of this radiation is the immediate vicinity of the central supermassive black hole (BH). Because of its low bolometric luminosity, the nucleus of M87 can be effectively transparent for γ-rays up to an energy of 10 TeV, which makes this source an ideal laboratory for the study of particle acceleration processes close to the BH event horizon. We critically analyze different possible radiation mechanisms in this region and argue that the observed very high energy γ-ray emission can be explained as the inverse Compton emission of ultrarelativistic electron-positron pairs produced through the development of an electromagnetic cascade in the BH magnetosphere. We demonstrate, through detailed numerical calculations of acceleration and radiation of electrons in the magnetospheric vacuum gap, that this pulsar magnetosphere-like scenario can satisfactorily explain the main properties of the TeV γ-ray emission from M87.

Inverse Compton e pair cascade model for the -ray production in massive binary LSI +61 303

We apply an inverse Compton e ± pair cascade model for γ-ray production in the massive binary system LSI +61° 303 assuming that electrons are accelerated already inside the inner part of the jet launched by the compact object. γ-ray spectra, affected by the cascade process, and lower energy spectra, from the synchrotron cooling of the highest energy electrons in the jet, are calculated as a function of the phase of this binary system. γ-ray spectra expected in such a model have different shape than those ones produced by electrons in the jet directly to observer. Moreover, the model predicts clear anticorrelation between γ-ray fluxes in the GeV (1-10 GeV) and TeV (>200 GeV) energy ranges with the peak of the TeV emission at the phase ∼0.5 (the peak half-width ranges between the phases ∼0.4-0.9, for the inclination of the binary system equal to 60°, and ∼0.4-0.1 for 30°). The fine features of TeV γ-ray emission (fluxes and spectral shapes) as a function of the phase of the binary system are consistent with recent observations reported by the MAGIC collaboration. Future simultaneous observations in the GeV energies (by the GLAST and AGILE telescopes) and in the TeV energies (by the MAGIC and VERITAS telescopes) should test other predictions of the considered model supporting or disproving the hypothesis of acceleration of electrons already in the inner part of the microquasar jets.

Channelled relativistic outflows in active galactic nuclei: analytic solutions for the evolution of particle spectra

Context. Calculations of highly energetic neutrino and TeV γ-ray emission from relativistic jets of Active Galactic Nuclei (AGN) are often based on a model that involves a collimated relativistic blast wave, in which the spectral evolution of energetic particles is determined by the interplay between the particle injection by sweep up of the interstellar medium, energy losses by radiation and diffusive escape. Aims. To date such models only have been solved numerically because of the highly non-linear nature of the time-dependent equations describing particle spectra and bulk energy loss. However it is difficult to see how parameters and groupings of parameters influence the resulting numerical solutions, except through intensive investigations of many numerical simulations. Therefore analytic solutions are particularly helpful. Methods. We provide exact mathematical solutions to a very broad class of AGN type models. By selecting different functional behaviors of parameter values, we cover a large compendium of possible situations. The comparison of the exact solutions with observational information can help to improve our understanding of the evolution of individual AGN. Exact solutions can also be used to provide controls on the appropropriateness and accuracy of numerical programs used to solve the equations. Results. We provide an analytical description of the evolution of proton spectra according to the pick-up model. We analyze the behavior of the particle spectra in the plasma frame. The solutions are determined by two competing processes: the deceleration of the jet plasmoid and particle cooling via radiation.

Neutrinos from Pulsar Environments

AbstractRecent calculations of the neutrino fluxes and spectra from pulsar magnetospheres and wind nebulae are reviewed. The neutrinos, produced in pp and pγ collisions via pion decays, are a signature of TeV ions accelerated electrostatically in the magnetosphere, in the wind termination shock (Fermi), or in the wind neutral sheet (wave surfing and/or reconnection). The fluxes and spectra are related to the energy and density of the accelerated ion beam and the densities of the target species, thereby constraining ion-loaded pulsar wind models originally developed to explain the variable wisps in pulsar-driven supernova remnants. The neutrino signal may be detectable by km2 telescopes (e.g. IceCube) and is correlated with TeV γ-ray emission. Related sources are also reviewed, such as early-phase post-supernova pulsar winds, pulsar-driven γ-ray-burst afterglows, and accreting neutron stars. The possibility of long baseline oscillation experiments, to search for fine splitting of neutrino mass eigenstates and non-radiative neutrino decays, is noted.

Ground-Based Gamma-Ray Detection of High Energy Galactic Sources: An Update

I review the present status of ground-based γ-ray astronomy, concentrating on the population of Galactic TeV sources. A number of new telescope systems are now being completed, and promise to yield exciting new discoveries, expanding rapidly the number of sources. The TeV Galactic sources today include a number of plerions, shell-type supernova remnants, an X-ray binary, and also one unidentified candidate. Their present status, and our understanding of their TeV γ-ray emission processes are summarized and some motivation driving development of the field is outlined.

Very High Energy γ-rays from AGN

AbstractEvidence of TeV γ-ray emission has been found for only a handful of active galactic nuclei, with detailed investigations limited to the blazars Mrk 421 and Mrk 501. TeV γ-ray astronomy, as the highest energy band, provides important information that is hard to obtain from longer wavelength electromagnetic radiation. The current status of TeV γ-ray studies of active galactic nuclei is summarized and our understanding of the high energy phenomena taking place in active galactic nuclei is outlined, with the prospects for future TeV γ-ray observations also considered.

TeV gamma rays expected from supernova remnants in different uniform interstellar media

Calculations of the expected TeV γ-ray emission, produced by accelerated cosmic rays (CRs) in nuclear collisions, from supernova remnants evolving in a uniform interstellar medium (ISM) are presented. The aim is to study the sensitivity of γ-ray production to a physical parameter set. Apart from its general proportionality to N H, it is shown that the γ-ray production essentially depends upon the ratio of the CR diffusion coefficient κ to a critical value κ crit =10(B 0/5 μG)(N H /0.3 cm −3) −1/3κ B , where B 0 and N H are the magnetic field and hydrogen number density of the ISM, and κ B denotes the Bohm diffusion coefficient. If κ is of the same order or lower than κ crit, then the peak TeV γ-ray flux in the Sedov evolutionary phase, normalized to a distance of 1 kpc, is about 10 −10(N H /0.3 cm −3) photons cm −2 s −1 . For a CR diffusion coefficient that is significantly larger than κ crit, the CR cutoff energy is less than 10 TeV, and the expected γ-ray flux at 1 TeV is considerably below the presently detectable level of 10 −12 photons cm −2 s −1 . The same is of course true for a supernova remnant in the rarified, so-called hot ISM.

Clusters of galaxies: magnetic fields and nonthermal emission

The nonthermal particle content of galaxy clusters should in part have a cosmological component generated during the early starburst phase of the member galaxies. This is reviewed in the framework of a simple cluster formation model suggested previously. It implies a nonthermal energy fraction of about 10 percent for the Intracluster gas. We also propose a mechanism for the early generation of Intracluster magnetic fields in terms of Galactic Winds. It results in typical field strenghts of 10 −7 G. Such comparatively weak fields are consistent with an inverse Compton origin of the excess EUV and hard X-ray emission of the Coma cluster, given the radio synchrotron emission. The required relativistic electrons must have been accelerated rather recently, less than a few billion years ago, presumably in cluster accretion shocks. This is in contrast to the hadronic nonthermal component which accumulates on cosmological time scales, and whose π 0-decay TeV γ-ray emission is expected to be larger, or of the same order as the inverse Compton TeV emission. This γ-radiation characterizes the energetic history of cluster formation and should be observable with future arrays of imaging atmospheric Cherenkov telescopes.

Constraints on the Extragalactic Infrared Background from Gamma-Ray Observations of Markarian 501

We use the new results of the HEGRA detector on the TeV γ-ray emission from Mrk 501 to set upper limits on the energy density of the cosmic infrared background (CIRB). Contrary to previous interpretations of the γ-ray spectrum of Mrk 421 as showing an intergalactic absorption cutoff at 5 TeV, the observed spectrum of Mrk 501 extends beyond 10 TeV and appears to be unattenuated by γ-γ collisions with the low-energy CIRB photons. The upper limits on the CIRB intensity—derived both assuming an a priori shape for the CIRB spectrum and without model-dependent assumptions—are thus quite strong and almost come into conflict with the observational evaluations based on deep surveys of extragalactic sources in the near- and mid-infrared. If spectra at TeV energies for extragalactic γ-ray sources like this for Mrk 501 are confirmed with improved statistics, we may be forced to conclude that the process of γ-γ interaction in the intergalactic space is more complex than expected and that the average intergalactic magnetic field is extremely weak (B<10−11 G).

TeV gamma-rays from proton blazars

Proton acceleration in nearby blazars can be diagnosed measuring their intense TeV γ-ray emission. Flux predictions for 1101+384 (Mrk421) and 1219+285 (ON231), both strong EGRET sources (0.1 – 10 GeV), are obtained from model spectra of unsaturated synchrotron pair cascades fitted to publicly available multifrequency data. An experimen tal effort to confirm the predicted emission in the range 1–10 TeV would be of great importance for the problems of the origin of cosmic rays, the era of galaxy formation and the cosmological distance scale.

Search for 10 TeV gamma-ray emission from active galactic nuclei with the Tibet air shower array

view Abstract Citations (7) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for 10 TeV Gamma-Ray Emission from Active Galactic Nuclei with the Tibet Air Shower Array Amenomori, M. ; Cao, Z. ; Dai, B. Z. ; Ding, L. K. ; Feng, Y. X. ; Feng, Z. Y. ; Hibino, K. ; Hotta, N. ; Huang, Q. ; Huo, A. X. ; Jia, H. Y. ; Jiang, G. Z. ; Jiao, S. Q. ; Kajino, F. ; Kasahara, K. ; Labaciren ; Liu, S. M. ; Mei, D. M. ; Meng, L. ; Meng, X. R. ; Mimaciren ; Mizutani, K. ; Mu, J. ; Nanjo, H. ; Nishizawa, M. ; Oguro, A. ; Ohnishi, M. ; Ohta, I. ; Ouchi, T. ; Ren, J. R. ; Saito, To. ; Sakata, M. ; Shi, Z. Z. ; Shibata, M. ; Shirai, T. ; Sugimoto, H. ; Sun, X. X. ; Taira, K. ; Tan, Y. H. ; Tateyama, N. ; Torii, S. ; Wang, H. ; Wen, C. Z. ; Yamamoto, Y. ; Yu, G. C. ; Yuan, P. ; Yuda, T. ; Zhang, C. S. ; Zhang, H. M. ; Zhang, L. and 4 more Abstract A search for 10 TeV γ-ray emission from 15 active galactic nuclei (AGNs) which were detected by EGRET was made with the Tibet air shower array installed at an elevation of 4300 m above sea level. The data set, taken in the period from 1990 June 18 through 1992 September 29 has been used to search for continuous emission as well as emission on the timescale of 1 day. No evidence for emission from any of the AGNs on any of the time scales examined was found. The 95% confidence level upper limit to the continuous flux is presented on each source, and in particular the result for Markarian 421 is compared with other experiments. Further observation of γ-rays at energies around 10 TeV from nearby AGNs will provide reliable information on the strength of the intergalactic background photon field. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174350 Bibcode: 1994ApJ...429..634A Keywords: Active Galactic Nuclei; Continuous Radiation; Cosmic Rays; Flux Density; Gamma Rays; Markarian Galaxies; Northern Sky; Quasars; Computerized Simulation; Fourier Transformation; Monte Carlo Method; Scintillation Counters; Tibet; Astrophysics; GALAXIES: ACTIVE; GALAXIES: NUCLEI; GALAXIES: QUASARS: INDIVIDUAL NAME: MARKARIAN 421; GAMMA RAYS: OBSERVATIONS; ISM: COSMIC RAYS full text sources ADS | data products NED (15) SIMBAD (14)

Pulsed TeV radiation from Hercules X-1

A four-year database (spring 1984 through spring 1987) of observations of Hercules X-1 by the Whipple Observatory Collaboration is being analyzed as a whole for evidence of TeV γ-ray emission. The full distribution of Rayleigh powers near the x-ray pulsar frequency differs significantly from the background distribution, giving evidence for sporadic emission at better than a 99% confidence level.