50 research outputs found
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
High energy resolution hard X-ray and gamma-ray imagers using CdTe diode devices
We developed CdTe double-sided strip detectors (DSDs or cross strip
detectors) and evaluated their spectral and imaging performance for hard X-rays
and gamma-rays. Though the double-sided strip configuration is suitable for
imagers with a fine position resolution and a large detection area, CdTe diode
DSDs with indium (In) anodes have yet to be realized due to the difficulty
posed by the segmented In anodes. CdTe diode devices with aluminum (Al) anodes
were recently established, followed by a CdTe device in which the Al anodes
could be segmented into strips. We developed CdTe double-sided strip devices
having Pt cathode strips and Al anode strips, and assembled prototype CdTe
DSDs. These prototypes have a strip pitch of 400 micrometer. Signals from the
strips are processed with analog ASICs (application specific integrated
circuits). We have successfully performed gamma-ray imaging spectroscopy with a
position resolution of 400 micrometer. Energy resolution of 1.8 keV (FWHM: full
width at half maximum) was obtained at 59.54 keV. Moreover, the possibility of
improved spectral performance by utilizing the energy information of both side
strips was demonstrated. We designed and fabricated a new analog ASIC, VA32TA6,
for the readout of semiconductor detectors, which is also suitable for DSDs. A
new feature of the ASIC is its internal ADC function. We confirmed this
function and good noise performance that reaches an equivalent noise charge of
110 e- under the condition of 3-4 pF input capacitance.Comment: 6 pages, 10 figures, accepted for publication in IEEE Transactions on
Nuclear Scienc
Results of a Si/CdTe Compton Telescope
We have been developing a semiconductor Compton telescope to explore the
universe in the energy band from several tens of keV to a few MeV. We use a Si
strip and CdTe pixel detector for the Compton telescope to cover an energy
range from 60 keV. For energies above several hundred keV, the higher
efficiency of CdTe semiconductor in comparison with Si is expected to play an
important role as an absorber and a scatterer. In order to demonstrate the
spectral and imaging capability of a CdTe-based Compton Telescope, we have
developed a Compton telescope consisting of a stack of CdTe pixel detectors as
a small scale prototype. With this prototype, we succeeded in reconstructing
images and spectra by solving the Compton equation from 122 keV to 662 keV. The
energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1
keV at 122 keV, respectively. The angular resolution obtained at 511 keV is
measured to be 12.2 degree (FWHM).Comment: 11 pages, 13 figures, presented at SPIE conference HARD X-RAY AND
GAMMA-RAY DETECTOR PHYSICS VII", San Diego, 2005. To be published in Proc.
SPIE 200