We report a study of extended γ-ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, which is likely to be the second case of a γ-ray detection from a ...star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1 7 × 2 1 around (l, b) = (25 0, 0 0). The γ-ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1 4 × 0 6. An ∼0 4 diameter subregion of one has a photon index of Γ = 1.53 0.15, and is spatially coincident with HESS J1837−069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ-ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ-ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ-ray emitting regions appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton, we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. We propose that the extended γ-ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.
This article reports the results of X-ray studies of the extended TeV γ-ray source VER J2019+368. Suzaku observations conducted to examine properties of the X-ray pulsar wind nebula (PWN) around PSR ...J2021+3651 revealed that the western region of the X-ray PWN has a source extent of with the major axis oriented to that of the TeV emission. The PWN-west spectrum was closely fitted by a power law for absorption at and a photon index of , with no obvious change in the index within the X-ray PWN. The measured X-ray absorption indicates that the distance to the source is much less than the inferred by radio data. Aside from the PWN, no extended emission was observed around PSR J2021+3651 even by Suzaku. Archival data from the XMM-Newton were also analyzed to complement the Suzaku observations, indicating that the eastern region of the X-ray PWN has a similar spectrum ( and ) and source extent up to at least along the major axis. The lack of significant change in the photon index and the source extent in X-ray are used to constrain the advection velocity or the diffusion coefficient for accelerated X-ray-producing electrons. A mean magnetic field of is required to account for the measured X-ray spectrum and reported TeV γ-ray spectrum. A model calculation of synchrotron radiation and inverse Compton scattering was able to explain of the reported TeV flux, indicating that the X-ray PWN is a major contributor of VER J2019+368.
We present an analysis of gamma-ray data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope in the region around supernova remnant (SNR) S147 (G180.0-1.7). A ...spatially extended gamma-ray source detected in an energy range of 0.2-10 GeV is found to coincide with SNR S147. We confirm its spatial extension at >5sigma confidence level. The gamma-ray flux is (3.8 + or - 0.6) x 10 super(-8) photons cm super(-2) s super(-1), corresponding to a luminosity of 1.3 x 10 super(34) (d/1.3 kpc) super(2) erg s super(-1) in this energy range. The gamma-ray emission exhibits a possible spatial correlation with the prominent H alpha filaments of SNR S147. There is no indication that the gamma-ray emission comes from the associated pulsar PSR J0538 + 2817. The gamma-ray spectrum integrated over the remnant is likely dominated by the decay of neutral pi mesons produced through the proton-proton collisions in the filaments. The reacceleration of the pre-existing cosmic rays and subsequent adiabatic compression in the filaments is sufficient to provide the energy density required of high-energy protons.
Centaurus B is a nearby radio galaxy positioned in the southern hemisphere close to the Galactic plane. Here we present a detailed analysis of about 43 months of accumulated Fermi-LAT data of the ...gamma -ray counterpart of the source initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku X-ny data. We confirm its detection at GeV photon energies and analyze the extension and variability of the gamma -ray source in the LAT dataset, in which it appears as a steady gamma -ray emitter. In this case, the observed gamma -ray flux is not likely to be produced within the lobes, but instead within the nuclear parts of the jet. By means of synchrotron self-Compton modeling, we show that this possibility could be consistent with the broad-band data collected for the unresolved core of Centaurus B, including the newly derived Suzaku spectrum.
We report a study of extended γ -ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope , which is likely to be the second case of a γ -ray detection from a ...star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1.°7 × 2.°1 around ( l , b ) = (25.°0, 0.°0). The γ -ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1.°4 × 0.°6. An ∼0.°4 diameter subregion of one has a photon index of Γ = 1.53 ± 0.15, and is spatially coincident with HESS J1837−069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 ± 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ -ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ -ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ -ray emitting regions appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton , we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. We propose that the extended γ -ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.
ABSTRACT
Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter Kop in Elber's effective SIF range ΔKeff(=Kmax−Kop). However, the ...parameters that replaced the traditional parameter Kop were based on different measurements or theoretical calculations, so it is difficult to distinguish their differences. This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip; the tests were carried out under different amplitude loading for structural steel. Based on these test results, differences of several parameter ΔKeff in literature are analysed and an improved two‐parameter driving force ΔKdrive(=(Kmax)n(ΔK∧)1‐n) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the ΔKdrive parameter was equally effective or better than ΔK(=Kmax−Kmin), ΔKeff(=Kmax−Kop) and ΔK*(= (Kmax)α(ΔK+)1−α) in correlating and predicting the R‐ratio effects on fatigue crack growth rate.
Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for ...the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.
In this paper, based on physical meanings of hysteresis loops denoting a relationship between loads and strains near the fatigue crack tip, variations of the tensile plastic zone in loading and the ...compressive plastic zone in unloading as well as the effects on acceleration, retardation and non-propagation in fatigue crack propagation are studied under different amplitude loadings. To the two closure types obtained from tests, the influence of each zone of a hysteresis loop upon fatigue crack propagation is evaluated and the effects of the compressive plastic zone at the crack tip on fatigue crack propagation are ascertained.
Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and many astrophysical ...processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling--a process known as active galactic nucleus feedback. Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 ± 10 kilometres per second in the region 30-60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 ± 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.
Polarization measurements in the hard X-ray band can provide crucial information about high energy emission at astrophysical objects. Such measurements require an instrument with high signal-to-noise ...ratio and high photon throughput for which the multilayer hard X-ray mirror is ideally suited. Future hard X-ray missions equipped with the multilayer mirror including ASTRO-H (Formerly NeXT) and NuStar are expected to detect hard X-ray sources in the flux range of
10
μ
Crab
. We expect a polarimeter mission using such mirrors to follow. Reflection off the mirror surface can introduce small but finite artificial polarization at the focal plane. We have conducted an experiment to set an upper limit for such polarization using a polarized hard X-ray beam at SPring-8 in Japan. In the experiment, reflectance of a multilayer surface has been measured as a function of the angle between the scattering plane and the hard X-ray polarization plane. The angular dependence of the measured reflectance can be translated to the artificial polarization. We have derived from the experimental results that the artificial polarization is no more than
±
0.8
%
at the scattering angle 0.51°. This upper limit ensures that we can measure polarization down to
∼
1
%
using the multilayer X-ray mirror.
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