共查询到20条相似文献，搜索用时 78 毫秒
1.
Francesco Miniati 《Monthly notices of the Royal Astronomical Society》2002,337(1):199-208
We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral π mesons generated in p–p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to ≲1 per cent . Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background. 相似文献
2.
Blazar emission of gamma rays and cosmic ray production of gamma rays in gas-rich clusters have been proposed recently as alternative sources of the high energy extragalactic diffuse gamma ray background radiation. We show that these sources also produce very different high energy extragalactic diffuse neutrino background radiations. An extragalactic neutrino background radiation may be detected by the new generation of large neutrino telescopes under construction and may be used to trace the origin of the extragalactic gamma radiation. 相似文献
3.
The origin of extragalactic diffuse gamma ray is not accurately known, especially because our suggestions are related to many
models that need to be considered either to compute the galactic diffuse gamma ray intensity or to consider the contribution
of other extragalactic structures while surveying a specific portion of the sky. More precise analysis of EGRET data however,
makes it possible to estimate the diffuse gamma ray in Coma supercluster (i.e., Coma\\backslash A1367 supercluster) direction with a value of $I\left( {E>{30}\,{\rm MeV}} \right)\simeq{1.9}\times {10}^{-{6}} {\rm cm}^{-{2}} {\rm s}^{-{1}}$I\left( {E>{30}\,{\rm MeV}} \right)\simeq{1.9}\times {10}^{-{6}} {\rm cm}^{-{2}} {\rm s}^{-{1}} , which is considered to be an upper limit for the diffuse gamma ray due to Coma supercluster. The related total intensity
(on average) is calculated to be ~5% of the actual diffuse extragalactic background. The calculated intensity makes it possible
to estimate the origin of extragalactic diffuse gamma ray. 相似文献
4.
We discuss the possibility of observing ultra high energy cosmic ray sources in high energy gamma rays. Protons propagating
away from their accelerators produce secondary electrons during interactions with cosmic microwave background photons. These
electrons start an electromagnetic cascade that results in a broad band gamma ray emission. We show that in a magnetized Universe
(B≳10−12 G) such emission is likely to be too extended to be detected above the diffuse background. A more promising possibility comes
from the detection of synchrotron photons from the extremely energetic secondary electrons. Although this emission is produced
in a rather extended region of size ∼10 Mpc, it is expected to be point-like and detectable at GeV energies if the intergalactic
magnetic field is at the nanogauss level.
相似文献
5.
K. N. Yu 《Astrophysics and Space Science》1987,136(1):1-10
A method is proposed to estimate the contribution from Seyfert galaxies and quasars to the diffuse 1 MeV background. First of all, we calculate the contribution from these active galactic nuclei (AGNs) to the 2 keV background using traditional methods. We then choose a suitable spectral X-ray index, which is found to be universal, to find the 1 MeV contribution from these AGNs by extrapolation. Results show that quasars generate about 40% of the 1 MeV background while Seyfert galaxies produce more than 40% taking into account the Penrose Compton Scattering gamma ray emissions. These results indicate that the 1 MeV background is likely to be generated by discrete objects. 相似文献
6.
The presence of a significant population of relic relativistic electrons - created at an early epoch of the Universe - has
been invoked to explain the diffuse EUV emission excess observed in a number of galaxy clusters. While the postulated inverse
Compton scattering of the 3° K background radiation by cosmic ray electrons might indeed be utilized as an important diagnostic
tool for the physical nature of the intracluster cosmic rays, it is shown here that continuous generation plus reacceleration
would be necessary if the conditions on the observed energy spectral distribution and energy supply rate are to be met in
the case of clusters with large radio halos.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Ruta Kale K. S. Dwarakanath Dharam Vir Lal Joydeep Bagchi Surajit Paul Siddharth Malu Abhirup Datta Viral Parekh Prateek Sharma Mamta Pandey-Pommier 《Journal of Astrophysics and Astronomy》2016,37(4):31
The intra-cluster and inter-galactic media that pervade the large scale structure of the Universe are known to be magnetized at sub-micro Gauss to micro Gauss levels and to contain cosmic rays. The acceleration of cosmic rays and their evolution along with that of magnetic fields in these media is still not well understood. Diffuse radio sources of synchrotron origin associated with the Intra-Cluster Medium (ICM) such as radio halos, relics and mini-halos are direct probes of the underlying mechanisms of cosmic ray acceleration. Observations with radio telescopes such as the Giant Metrewave Radio Telescope, the Very Large Array and the Westerbork Synthesis Radio Telescope have led to the discoveries of about 80 such sources and allowed detailed studies in the frequency range 0.15–1.4 GHz of a few. These studies have revealed scaling relations between the thermal and non-thermal properties of clusters and favour the role of shocks in the formation of radio relics and of turbulent re-acceleration in the formation of radio halos and mini-halos. The radio halos are known to occur in merging clusters and mini-halos are detected in about half of the cool-core clusters. Due to the limitations of current radio telescopes, low mass galaxy clusters and galaxy groups remain unexplored as they are expected to contain much weaker radio sources. Distinguishing between the primary and the secondary models of cosmic ray acceleration mechanisms requires spectral measurements over a wide range of radio frequencies and with high sensitivity. Simulations have also predicted weak diffuse radio sources associated with filaments connecting galaxy clusters. The Square Kilometre Array (SKA) is a next generation radio telescope that will operate in the frequency range of 0.05–20 GHz with unprecedented sensitivities and resolutions. The expected detection limits of SKA will reveal a few hundred to thousand new radio halos, relics and mini-halos providing the first large and comprehensive samples for their study. The wide frequency coverage along with sensitivity to extended structures will be able to constrain the cosmic ray acceleration mechanisms. The higher frequency (>5 GHz) observations will be able to use the Sunyaev–Zel’dovich effect to probe the ICM pressure in addition to tracers such as lobes of head–tail radio sources. The SKA also opens prospects to detect the ‘off-state’ or the lowest level of radio emission from the ICM predicted by the hadronic models and the turbulent re-acceleration models. 相似文献
8.
S. V. Damle R. R. Daniel George Joseph P. J. Lavakare 《Astrophysics and Space Science》1971,14(2):473-479
Measurements have been made on the cosmic gamma rays of energy between 0.25 and 4.2 MeV from a balloon experiment made near the geomagnetic equator using a collimated 7.6 cm×7.6 cm NaI(T1) crystal assembly. The depth-intensity curves obtained were used to estimate the contribution due to the diffuse cosmic gamma rays in the above energy interval; an unfolding of the counting rates was then performed to obtain the energy spectrum. It is found that a power law fitted to the present data points has a spectral index of –1.8±0.2. A critical examination is then made of all the observational data between 1 keV and 100 MeV to deduce information on the spectral shape in this energy region. Upper limits on low energy gamma ray fluxes from Sco X-1 and the Galactic centre region are also reported. 相似文献
9.
L. Bassani R. C. Butler A. J. Dean G. Di Cocco F. Perotti G. Villa 《Astrophysics and Space Science》1982,82(1):199-207
Three active galaxies, generally classified as Seyferts, have been discovered recently to be powerful, low energy -ray sources. The similarity between their spectral characteristics and those of the cosmic background at -ray energies suggests that these objects could make a significant contribution to this diffuse flux. This contribution has been assessed using two different number densities of -ray-emitting Seyfert galaxies based on optical and X-ray data. The comparison of the estimated and measured diffuse -ray background intensities is used to gain a deeper understanding of the metabolism of Seyfert galaxies. 相似文献
10.
《New Astronomy》2016
We developed a method that allows us to estimate the high energy gamma ray luminosity of intermediate mass black holes (IMBH) located in the central regions of globular clusters. Our calculations are based on the relation between the relativistic jet kinetic power and the luminosity of the gamma ray radiation that is produced by the jet itself. The power of a relativistic jet is determined via the Blandford–Znajek mechanism. Our calculations show that the contribution of the central IMBH in gamma ray luminosity is comparable with the contribution of the population of millisecond pulsars. 相似文献
11.
With the help of empirical data concerning the latitudinal distribution of galactic gamma rays the contribution of inverse Compton scattered gamma rays is calculated using various models concerning the distribution of high energy cosmic ray electrons perpendicular to the galactic plane. It is shown that gamma ray astronomy from regions with vanishing stellar and interstellar matter densities at energies greater than 100 MeV provides instructive information on the cosmic ray electron density. We find evidence for the existence of a broad galactic electron disk with a total thickness of at least 6.4 kpc. The uncertainties of the cosmic ray electron spectrum measurements above 100 GeV imply an additional uncertainty in the inverse Compton source function of at least a factor 6. 相似文献
12.
Shigemori K Ditmire T Remington BA Yanovsky V Ryutov D Estabrook KG Edwards MJ MacKinnon AJ Rubenchik AM Keilty KA Liang E 《The Astrophysical journal》2000,534(2):L159-L162
We assume that internal shocks of gamma-ray bursts (GRBs) consist of multiple sub-jets with a collimation half-angle of about several times gamma-1i, where gammai is the Lorentz factor of each sub-jet. If by chance a sub-jet is first emitted off-axis from the line of sight, the observed peak energy can be in the X-ray region. Next, if by chance a subsequent sub-jet is emitted along the line of sight, then the peak energy will be in the gamma-ray region and the gamma ray may arrive after the X-ray precursor from the former sub-jet depending on parameters. This model predicts a new class of GRBs with extremely weak and short gamma-ray emission but X-ray precursors and/or postcursors as well as an afterglow. 相似文献
13.
This review describes the basic theory of cosmic ray acceleration by shocks including the plasma instabilities confining cosmic rays near the shock, the effect of the magnetic field orientation, the maximum cosmic ray energy and the shape of the cosmic ray spectrum. Attention is directed mainly towards Galactic cosmic rays accelerated by supernova remnants. 相似文献
14.
D. E. Roa R. K. Smither X. Zhang K. Nie Y. Y. Shieh N. S. Ramsinghani N. Milne J. V. Kuo J. L. Redpath M. S. A. L. Al-Ghazi P. Caligiuri 《Experimental Astronomy》2005,20(1-3):229-239
The objective of this project is to develop and construct an innovative imaging system for nuclear medicine and molecular imaging that uses photon diffraction and is capable of generating 1–2 mm spatial resolution images in two or three dimensions. The proposed imaging system would be capable of detecting radiopharmaceuticals that emit 100–200 keV gamma rays which are typically used in diagnostic nuclear medicine and in molecular imaging. The system is expected to be optimized for the 140.6 keV gamma ray from a Tc-99m source, which is frequently used in nuclear medicine. This new system will focus the incoming gamma rays in a manner analogous to a magnifying glass focusing sunlight into a small focal point on a detector's sensitive area. Focusing gamma rays through photon diffraction has already been demonstrated with the construction of a diffraction lens telescope for astrophysics and a scaled-down lens for medical imaging, both developed at Argonne National Laboratory (ANL). In addition, spatial resolutions of 3 mm have been achieved with a prototype medical lens. The proposed imaging system would be comprised of an array of photon diffraction lenses tuned to diffract a specific gamma ray energy (within 100–200 keV) emitted by a common source. The properties of photon diffraction make it possible to diffract only one specific gamma ray energy at a time, which significantly reduces scattering background. The system should be sufficiently sensitive to the detection of small concentrations of radioactivity that can reveal potential tumor sites at their initial stages of development. Moreover, the system's sensitivity would eliminate the need for re-injecting a patient with more radiopharmaceutical if this patient underwent a prior nuclear imaging scan. Detection of a tumor site at its inception could allow for an earlier initiation of treatment and wider treatment options, which can potentially improve the chances for cure. 相似文献
15.
D. Koutroumpa 《Astronomische Nachrichten》2012,333(4):341-346
About 15 years ago, charge exchange (CX) X‐ray emission was discovered in comet observations, and was identified as the radiative decay of excited states of highly‐charge solar wind ions populated in collisions with neutral cometary material. This non‐thermal X‐ray emission mechanism is now generally acknowledged in planetary environments (e.g. Mars, Earth), as well as interstellar atoms sweeping through the heliosphere. In this paper I present the most recent improvements made in simulations of the heliospheric CX X‐ray emission. The model results are compared to X‐ray data from Suzaku, XMM‐Newton and Chandra spanning over a 10‐year period, and some conclusions are drawn on the heliospheric contribution to the diffuse soft X‐ray background. The solar system CX X‐ray sources can serve as prototypes in terms of modeling and diagnostics to more distant astrophysical objects where CX emission signatures are being discovered (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
The IceCube experiment has detected two neutrinos with energies between 1 and 10 PeV. They might have originated from Galactic or extragalactic sources of cosmic rays. In the present work we consider hadronic interactions of the diffuse very high energy cosmic rays with the interstellar matter within our Galaxy to explain the PeV neutrino events detected in IceCube. We also expect PeV gamma ray events along with the PeV neutrino events if the observed PeV neutrinos were produced within our Galaxy in hadronic interactions. PeV gamma rays are unlikely to reach us from sources outside our Galaxy due to pair production with cosmic background radiation fields. We suggest that in future with simultaneous detections of PeV gamma rays and neutrinos it would be possible to distinguish between Galactic and extragalactic origins of very high energy neutrinos. 相似文献
17.
Gamma-ray background counting rates encountered in astronomy observations are calculated for a double Compton scatter telescope. Backgrounds not eliminated by the usual growth curve could be produced by albedo neutrons and/or cosmic ray protons interacting with the carbon and/or hydrogen of the detector. They are the albedo neutron-carbon interaction gamma-rays, cosmic ray proton interaction delayed gamma rays and the moderated albedo neutron-proton photocapture gamma rays. It is decisive to know the contribution of these backgrounds, because they must be subtracted before the cosmic diffuse flux can be determined. Estimates of the neutron induced background events in a Compton telescope show that they might contribute a considerable fraction of the counting rate. In the near future the calculations will be checked with a calibrated neutron beam. 相似文献
18.
The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma-rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma-ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non-thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of
19.
The nature of the diffuse cosmic background in the low -ray energy range has been widely discussed but not definitively solved. Unresolved active galaxies have become good candidates for its origin ever since they have been identified as -ray emitting objects. In particular, the summed contribution of Seyfert galaxies is expected to be dominant to such an extent that a straight forward calculation, based on their volume emissivity, predicts a considerable excess above the observed level of the isotropic background flux. In this letter we explore different ways to reconcile the observational data on these active galactic nuclei with the measured intensity of the cosmic diffuse -radiation. 相似文献
20.
Neutrino production of radio Cherenkov signals in the Moon is the object of radio telescope observations. Depending on the energy range and detection parameters, the dominant contribution to the neutrino signal may come from interactions of the neutrino on the Moon facing the telescope, rather than neutrinos that have traversed a portion of the Moon. Using the approximate analytic expression of the effective lunar aperture from a recent paper by Gayley, Mutel and Jaeger, we evaluate the background from cosmic ray interactions in the lunar regolith. We also consider the modifications to the effective lunar aperture from generic non-standard model neutrino interactions. A background to neutrino signals are radio Cherenkov signals from cosmic ray interactions. For cosmogenic neutrino fluxes, neutrino signals will be difficult to observe because of low neutrino flux at the high energy end and large cosmic ray background in the lower energy range considered here. We show that lunar radio detection of neutrino interactions is best suited to constrain or measure neutrinos from astrophysical sources and probe non-standard neutrino-nucleon interactions such as microscopic black hole production. 相似文献