Junichiro Katsuta

FERMI LARGE AREA TELESCOPE DISCOVERY OF GeV GAMMA-RAY EMISSION FROM THE VICINITY OF SNR W44

We report the detection of GeV γ-ray emission from the molecular cloud complex that surrounds the supernova remnant (SNR) W44 using the Large Area Telescope on board Fermi. While the previously reported γ-ray emission from SNR W44 is likely to arise from the dense radio-emitting filaments within the remnant, the γ-ray emission that appears to come from the surrounding molecular cloud complex can be ascribed to the cosmic rays (CRs) that have escaped from W44. The non-detection of synchrotron radio emission associated with the molecular cloud complex suggests the decay of π0 mesons produced in hadronic collisions as the γ-ray emission mechanism. The total kinetic energy channeled into the escaping CRs is estimated to be W esc ~ (0.3-3) × 1050 erg, in broad agreement with the conjecture that SNRs are the main sources of Galactic CRs.

Fermi Large Area Telescope Observation of Supernova Remnant S147

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 >5? confidence level. The gamma-ray flux is (3.8 ? 0.6) ? 10?8 photons cm?2 s?1, corresponding to a luminosity of 1.3 ? 1034 (d/1.3 kpc)2?erg?s?1 in this energy range. The gamma-ray emission exhibits a possible spatial correlation with the prominent H? 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 ? 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.

The Hard X-ray Imager (HXI) for the ASTRO-H mission

The 6th Japanese X-ray satellite, ASTRO-H, is scheduled for launch in 2015. The hard X-ray focusing imaging system will observe astronomical objects with the sensitivity for detecting point sources with a brightness of 1/100,000 times fainter than the Crab nebula at > 10 keV. The Hard X-ray Imager (HXI) is a focal plane detector 12 m below the hard X-ray telescope (HXT) covering the energy range from 5 to 80 keV. The HXI is composed of a stacked Si/CdTe semiconductor detector module and surrounding BGO scintillators. The latter work as active shields for efficient reduction of background events caused by cosmic-ray particles, cosmic X-ray background, and in-orbit radiation activation. In this paper, we describe the detector system, and present current status of flight model development, and performance of HXI using an engineering model of HXI.

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 γ-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 γ-ray source in the LAT dataset, in which it appears as a steady γ-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 γ-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 γ-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 γ-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.

Inflight calibration and performance of the hard X-ray detector (HXD) onboard Suzaku

The hard X-ray detector (HXD) onboard Suzaku covers an energy range of 8-700 keV, and thus in combination with the CCD camera (XIS) gives us an opportunity of wide-band X-ray observations of celestial sources with a good sensitivity over the 0.3-700 keV range. All of 64 Si-PIN photo diodes, 16 GSO/BGO phoswich scintillators, and 20 anti-coincidence BGO scintillators in the HXD are working well since the Suzaku launch on July 2005. The rejection of background events is confirmed to be as effective as expected, and accordingly the HXD achieved the lowest background level of the previously or currently operational missions sensitive in the comparable energy range. The energy and angular responses and timing have been continuously calibrated by the data from the Crab nebula, X-ray pulsars, and other sources, and at present several % accuracy is obtained. Even though the HXD does not perform simultaneous background observations, it detected weak sources with a flux as low as ~0.5 mCrab; stars, X-ray binaries, supernova remnants, active galactic nuclei, and galaxy clusters. Extensive studies of background subtraction enables us to study weaker sources.

Extended Gamma-Ray Emission from the G25.0+0.0 Region: A Star-forming Region Powered by the Newly Found OB Association?

We report a study of extended

Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi ’s measurement in a low Earth orbit

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Hard x-ray imager onboard Hitomi (ASTRO-H)

-ray emission with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope, which is likely to be the second case of a

High sensitivity balloon-borne hard X-ray/soft Gamma-Ray Polarimeter PoGOLite

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In-orbit performance and calibration of the Hard X-ray Imager onboard Hitomi (ASTRO-H)

-ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region,