Development of a Si/CdTe semiconductor Compton telescope

We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtain a high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results from the prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of a double-sided Si strip detector (DSSD) and CdTe pixel detectors, combined with low noise analog LSI, VA32TA. With this detector, we obtained Compton reconstructed images and spectra from line gamma-rays ranging from 81 keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and 356 keV, respectively, and the angular resolution is 9.9 degrees and 5.7 degrees at 122 keV and 356 keV, respectively.Comment: 12 pages, 14 figures, submitted to SPIE conference proceedings vol. 5501, "High-Energy Detectors in Astronomy", Glasgow UK, 6/21-6/24 200

Unraveling the Nature of Unidentified High Galactic Latitude Fermi/LAT Gamma-ray Sources with Suzaku

We report on the results of deep X-ray follow-up observations of four unidentified Fermi/LAT gamma-ray sources at high Galactic latitudes using Suzaku. The studied objects were detected with high significance during the first 3 months of Fermi/LAT operation, and subsequently better localized in the Fermi/LAT 1 year catalog (1FGL). Possible associations with pulsars and active galaxies have subsequently been discussed, and our observations provide an important contribution to this debate. In particular, an X-ray point source was found within the 95% confidence error circle of 1FGL J1231.1-1410. X-ray spectrum is well-fitted by a blackbody with an additional power-law. This supports the recently claimed identification of this source with a millisecond pulsar (MSP) PSR J1231-1411. Concerning 1FGL J1311.7-3429, two X-ray sources were found within the LAT error circle. Even though the X-ray spectral and variability properties were accessed, their nature and relationship with the gamma-ray source remain uncertain. We found several weak X-ray sources in the field of 1FGL J1333.2+5056, one coinciding with CLASS J1333+5057. We argue the available data are consistent with the association between these two objects. Finally, we have detected an X-ray source in the vicinity of 1FGL J2017.3+0603. This object was recently suggested to be associated with a newly discovered MSP PSR J2017+0603, because of the spatial-coincidence and the gamma-ray pulse detection. We have only detected the X-ray counterpart of the CLASS J2017+0603, while we determined an X-ray flux upper limit at the pulsar position. All in all, our studies indicate while a significant fraction of unidentified high Galactic latitude gamma-ray sources is related to the pulsar and blazar phenomena, associations with other classes of astrophysical objects are still valid options.Comment: Accepted for publication in the Ap

A Suzaku Observation of the Low-Ionization Fe-Line Emission from RCW 86

The newly operational X-ray satellite Suzaku observed the southwestern quadrant of the supernova remnant (SNR) RCW 86 in February 2006 to study the nature of the 6.4 keV emission line first detected with the Advanced Satellite for Cosmology and Astronomy (ASCA). The new data confirm the existence of the line, localizing it for the first time; most of the line emission is adjacent and interior to the forward shock and not at the locus of the continuum hard emission. We also report the first detection of a 7.1 keV line that we interpret as the K-beta emission from low-ionization iron. The Fe-K line features are consistent with a non-equilibrium plasma of Fe-rich ejecta with n_{e}t <~ 10^9 cm^-3 s and kT_{e} ~ 5 keV. This combination of low n_{e}t and high kT_{e} suggests collisionless electron heating in an SNR shock. The Fe K-alpha line shows evidence for intrinsic broadening, with a width of 47 (34--59) eV (99% error region). The difference of the spatial distributions of the hard continuum above 3 keV and the Fe-K line emission support a synchrotron origin for the hard continuum.Comment: 6 pages with 6 figures. Accepted for PASJ Suzaku Special Issue (vo. 58, sp.1