Measurement of the trailing edge of cosmic-ray track signals from a round-tube drift chamber

The trailing edge of tube drift-chamber signals for charged particles is expected to provide information concerning the particle passage time. This information may be useful for separating meaningful signals from overlapping garbage at high-rate experiments, such as the future LHC experiments. We carried out a cosmic-ray test using a small tube chamber in order to investigate the feasibility of this idea. We achieved a trailing-edge time resolution of 12 ns in rms by applying simple pulse shaping to eliminate a signal tail. A comparison with a Monte Carlo simulation indicates the importance of well-optimized signal shaping to achieve good resolution. The resolution may be further improved with better shaping.Comment: 13 pages including 9 figure

Prospect for Future MeV Gamma-ray Active Galactic Nuclei Population Studies

While the X-ray, GeV gamma-ray, and TeV gamma-ray skies have been extensively studied, the MeV gamma-ray sky is not well investigated after the Imaging Compton Telescope (COMPTEL) scanned the sky about two decades ago. In this paper, we investigate prospects for active galactic nuclei population studies with future MeV gamma-ray missions using recent spectral models and luminosity functions of Seyfert and flat spectrum radio quasars (FSRQs). Both of them are plausible candidates as the origins of the cosmic MeV gamma-ray background. If the cosmic MeV gamma-ray background radiation is dominated by non-thermal emission from Seyferts, the sensitivity of 10^-12 erg cm^-2 s^-1 is required to detect several hundred Seyferts in the entire sky. If FSRQs make up the cosmic MeV gamma-ray background, the sensitivity of ~4 x 10^-12 erg cm^-2 s^-1 is required to detect several hundred FSRQs following the recent FSRQ X-ray luminosity function. However, based on the latest FSRQ gamma-ray luminosity function, with which FSRQs can explain up to ~30% of the MeV background, we can expect several hundred FSRQs even with the sensitivity of 10^-11 erg cm^-2 s^-1 which is almost the same as the sensitivity goal of the next generation MeV telescopes.Comment: 9 pages, 5 figures, accepted for publication in PAS

Sensitivity of the Fe Kα\alpha Compton shoulder to the geometry and variability of the X-ray illumination of cosmic objects

In an X-ray reflection spectrum, a tail-like spectral feature generated via Compton downscattering, known as a Compton shoulder (CS), appears at the low-energy side of the iron K$\alpha$ line. Despite its great diagnostic potential, its use as a spectral probe of the reflector has been seriously limited due to observational difficulties and modelling complexities. We revisit the basic nature of the CS by systematic investigation into its dependence on spatial and temporal parameters. The calculations are performed by Monte Carlo simulations for sphere and slab geometries. The dependence is obtained in a two-dimensional space of column density and metal abundance, demonstrating that the CS solves parameter degeneration between them which was seen in conventional spectral analysis using photoelectric absorption and fluorescence lines. Unlike the iron line, the CS does not suffer from any observational dependence on the spectral hardness. The CS profile is highly dependent on the inclination angle of the slab geometry unless the slab is Compton-thick, and the time evolution of the CS is shown to be useful to constrain temporal information on the source if the intrinsic radiation is variable. We also discuss how atomic binding of the scattering electrons in cold matter blurs the CS profile, finding that the effect is practically similar to thermal broadening in a plasma with a moderate temperature of ~5 eV. Spectral diagnostics using the CS is demonstrated with grating data of X-ray binary GX 301−2, and will be available in future with high-resolution spectra of active galactic nuclei obtained by microcalorimeters.JSPS KAKENHI (Grant IDs: 24740190, 24105007), Advanced Leading graduate school for Photon Science (ALPS

Densification of Ca-doped alumina nanopowders prepared by a new sol-gel route with seeding

ArticleJOURNAL OF THE EUROPEAN CERAMIC SOCIETY. 28(13):2479-2485(2008)journal articl

Fermi-LAT and Suzaku Observations of the Radio Galaxy Centaurus B

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-ray 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. The X-ray core of Centaurus B is detected as a bright source of a continuum radiation. We do not detect however any diffuse X-ray emission from the known radio lobes, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. Two scenarios that connect the X-ray and gamma-ray properties are considered. In the first one, we assume that the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. In this case, modeling the inverse-Compton emission shows that the observed gamma-ray flux of the source may in principle be produced within the lobes. This association would imply that efficient in-situ acceleration of the radiating electrons is occurring and that the lobes are dominated by the pressure from the relativistic particles. In the second scenario, with the diffuse X-ray emission well below the Suzaku upper limits, the lobes in the system are instead dominated by the magnetic pressure. 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.Comment: Accepted for publication in A&A. 11 page

Non-equivalence between Heisenberg XXZ spin chain and Thirring model

The Bethe ansatz equations for the spin 1/2 Heisenberg XXZ spin chain are numerically solved, and the energy eigenvalues are determined for the anti-ferromagnetic case. We examine the relation between the XXZ spin chain and the Thirring model, and show that the spectrum of the XXZ spin chain is different from that of the regularized Thirring model.Comment: 10 pages. 2figure