We have examined the surface-channeling of 550keV protons on electron-bombarded KBr(001) surfaces at grazing incidence. On the surface, electron-stimulated desorption (ESD) resulting from the ...irradiation of 5keV electrons changes the surface morphology. In order to investigate the change of the surface morphology, the luminous intensity distributions observed on a fluorescent screen (scattering patterns) of the reflected protons under the surface-channeling conditions are measured. Normalized specular intensity of the protons oscillates, and the results of computer simulations show that the period of the intensity oscillation agrees with the period of layer-by-layer desorption. The measured period of the oscillation is comparable to the simulated one, i.e., the period of the desorption, however, the measured amplitude of the oscillation is weak. This shows that the layer-by-layer desorption of the experimental surface is observed but is not as remarkable as that of the perfect surface introduced in the simulation.
We present optical and near-infrared multi-band linear polarimetry of the highly reddened Type Ia supernova (SN) 2014J that appeared in M82. SN 2014J exhibits large polarization at shorter ...wavelengths, e.g., 4.8% in the B band, which decreases rapidly at longer wavelengths, while the position angle of the polarization remains at approximately 40degrees over the observed wavelength range. These polarimetric properties suggest that the observed polarization is likely predominantly caused by the interstellar dust within M82. Further analysis shows that the polarization peaks at a wavelengths much shorter than those obtained for the Galactic dust. The wavelength dependence of the polarization can be better described by an inverse power law rather than by the Serkowski law for Galactic interstellar polarization. These points suggest that the nature of the dust in M82 may be different from that in our Galaxy, with polarizing dust grains having a mean radius of <0.1 mum.
The blazar AO 0235+164 (z = 0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by ...Fermi, contemporaneous observations were carried out from the radio to gamma -ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASPWEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the gamma -ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 R sub(g). We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
ABSTRACT The hard X-ray detector (HXD) on board Suzaku measured soft γ-rays from the SN Ia SN2014J at 77 2 days after the explosion. Although the confidence level of the signal is about 90% (i.e., 2 ...), the 3 upper limit has been derived at <2.2 × 10−4 ph s−1 cm−2 in the 170-250 keV band as the first independent measurement of soft γ-rays with an instrument other than INTEGRAL. For this analysis, we have examined the reproducibility of the NXB model of HXD/GSO using blank sky data. We find that the residual count rate in the 90-500 keV band is distributed around an average of 0.19% with a standard deviation of 0.42% relative to the NXB rate. The averaged residual signals are consistent with that expected from the cosmic X-ray background. The flux of SN2014J derived from Suzaku measurements taken in one snapshot at t = 77 2 days after the explosion is consistent with the INTEGRAL values averaged over the period between t = 50 and 100 days and also with explosion models of single or double degenerate scenarios. Being sensitive to the total ejecta mass surrounding the radioactive material, the ratio between continuum and line flux in the soft gamma-ray regime might distinguish different progenitor models. The Suzaku data have been examined with this relation at t = 77 2 days, but could not distinguish models between single and double degenerate-progenitors. We disfavor explosion models with larger 56Ni masses than 1 M , from our 1 error on the 170-250 keV X-ray flux of (1.2 0.7) × 10−4 ph s−1 cm−2.
The Geostationary Operational Environmental Satellite (GOES) M2-class solar flare, SOL2010-06-12T00: 57, was modest in many respects yet exhibited remarkable acceleration of energetic particles. The ...flare produced an similar to 50 s impulsive burst of hard X-and gamma-ray emission up to at least 400 MeV observed by the Fermi Gamma-ray Burst Monitor and Large Area Telescope experiments. The remarkably similar hard X-ray and high-energy gamma-ray time profiles suggest that most of the particles were accelerated to energies greater than or similar to 300 MeV with a delay of similar to 10 s from mildly relativistic electrons, but some reached these energies in as little as similar to 3 s. The gamma-ray line fluence from this flare was about 10 times higher than that typically observed from this modest GOES class of X-ray flare. There is no evidence for time-extended >100 MeV emission as has been found for other flares with high-energy gamma-rays.
Context. The Cygnus region hosts a giant molecular-cloud complex that actively forms massive stars. Interactions of cosmic rays with interstellar gas and radiation fields make it shine at γ-ray ...energies. Several γ-ray pulsars and other energetic sources are seen in this direction. Aims. In this paper we analyze the γ-ray emission measured by the Fermi Large Area Telescope (LAT) in the energy range from 100 MeV to 100 GeV in order to probe the gas and cosmic-ray content on the scale of the whole Cygnus complex. The γ-ray emission on the scale of the central massive stellar clusters and from individual sources is addressed elsewhere. Methods. The signal from bright pulsars is greatly reduced by selecting photons in their off-pulse phase intervals. We compare the diffuse γ-ray emission with interstellar gas maps derived from radio/mm-wave lines and visual extinction data. A general model of the region, including other pulsars and γ-ray sources, is sought. Results. The integral H i emissivity above 100 MeV averaged over the whole Cygnus complex amounts to 2.06 ± 0.11 (stat.) -0.84+0.15(syst.) × 10-26 photons s-1 sr-1 H-atom-1, where the systematic error is dominated by the uncertainty on the H i opacity to calculate its column densities. The integral emissivity and its spectral energy distribution are both consistent within the systematics with LAT measurements in the interstellar space near the solar system. The average XCO = N(H2)/WCO ratio is found to be 1.68 ± 0.05 (stat.) -0.10+0.87(HI opacity) × 1020 molecules cm-2 (K km s-1)-1, consistent with other LAT measurements in the Local Arm. We detect significant γ-ray emission from dark neutral gas for a mass corresponding to ~40% of what is traced by CO. The total interstellar mass in the Cygnus complex inferred from its γ-ray emission amounts to 8-1+5 × 106 M⊙ at a distance of 1.4 kpc. Conclusions. Despite the conspicuous star formation activity and high masses of the interstellar clouds, the cosmic-ray population in the Cygnus complex averaged over a few hundred parsecs is similar to that of the local interstellar space.
We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E > 100 GeV) gamma -ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS ...0426-380. The null hypothesis that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 5.5sigma confidence level. We therefore claim that at least one of the two VHE photons is securely associated with PKS 0426?380, making it the most distant VHE emitter known to date. The results are in agreement with recent Fermi-LAT constraints on the extragalactic background light (EBL) intensity, which imply a z Asymptotically = to 1 horizon for Asymptotically = to100 GeV photons. The LAT detection of the two VHE gamma -rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower gamma -ray energies. Modeling the gamma -ray continuum of PKS 0426-380 with daily bins revealed a significant spectral hardening around the time of the first VHE event detection (LAT photon index Gamma Asymptotically = to 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in gamma -rays during the flaring epochs. An additional flat component is possibly present above several tens of GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ~8 month high state.
Here, we report on a detailed investigation of the high-energy γ-ray emission from NGC 1275, a well-known radio galaxy hosted by a giant elliptical located at the center of the nearby Perseus ...cluster. With the increased photon statistics, the center of the γ-ray-emitting region is now measured to be separated by only 0.46 arcmin from the nucleus of NGC 1275, well within the 95% confidence error circle with radius ≃1.5 arcmin. Early Fermi Large Area Telescope (LAT) observations revealed a significant decade-timescale brightening of NGC 1275 at GeV photon energies, with a flux about 7 times higher than the one implied by the upper limit from previous EGRET observations. With the accumulation of one year of Fermi-LAT all-sky-survey exposure, we now detect flux and spectral variations of this source on month timescales, as reported in this paper. The average >100 MeV γ-ray spectrum of NGC 1275 shows a possible deviation from a simple power-law shape, indicating a spectral cutoff around an observed photon energy of εγ = 42.2 ± 19.6 GeV, with an average flux of Fγ = (2.31 ± 0.13) × 10–7 photons cm–2 s–1 and a power-law photon index, Γγ = 2.13 ± 0.02. The largest γ-ray flaring event was observed in 2009 April-May and was accompanied by significant spectral variability above εγ ≳ 1-2 GeV. The γ-ray activity of NGC 1275 during this flare can be described by a hysteresis behavior in the flux versus photon index plane. The highest energy photon associated with the γ-ray source was detected at the very end of the observation, with the observed energy of εγ = 67.4 GeV and an angular separation of about 2.4 arcmin from the nucleus. In this paper we present the details of the Fermi-LAT data analysis, and briefly discuss the implications of the observed γ-ray spectral evolution of NGC 1275 in the context of γ-ray blazar sources in general.
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