寺田 幸功

Five on-plane regions within +/-0.degrees 8 of the galactic center were observed with the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS) aboard Suzaku. From all regions, significant hard X-ray emission was detected with HXD-PIN up to 40 keV, in addition to the extended plasma emission which is dominant in the XIS band. The hard X-ray signals are inferred to come primarily from a spatially extended source, rather than from a small number of bright discrete objects. Contributions to the HXD data from catalogued X-ray sources, typically brighter than 1 mCrab, were estimated and removed using information from Suzaku and other satellites. Even after this removal, the hard X-ray signals remained significant, exhibiting a typical 12-40keV surface brightness of 4 x 10(-10) erg cm(-2) s(-1) deg(-2) and power-law-like spectra with a photon index of 1.8. Combined fittings to the XIS and HXD-PIN spectra confirm that a separate hard tail component is superposed onto the hot thermal emission, confirming a previous report based on the XIS data. Over the 5-40 keV band, the hard tail is spectrally approximated by a power law of photon index similar to 2, but better by those with somewhat convex shapes. Possible origins of the extended hard X-ray emission are discussed.

The transient X-ray binary pulsar A0535+262 was observed with Suzaku on 2005 September 14 when the source was in the declining phase of the August-September minor outburst. The similar to 103 s X-ray pulse profile was strongly energy dependent, with a double-peaked profile in the soft X-ray energy band (< 3 keV) and a single-peaked smooth profile in hard X-rays. The width of the primary dip is found to increase with energy. The broadband energy spectrum of the pulsar is well described with a negative and positive power law with exponential (NPEX) continuum model, along with a blackbody component for soft excess. A weak iron K alpha emission line with an equivalent width similar to 25 eV was detected in the source spectrum. The blackbody component is found to be pulsating over the pulse phase, implying that the accretion column and/or the inner edge of the accretion disk may be the possible emission site of the soft excess in A0535+262. The higher value of the column density is believed to be the cause of the secondary dip in the soft X-ray energy band. The iron line equivalent width is found to be constant (within errors) over the pulse phase. However, a sinusoidal type of flux variation of the iron emission line, in phase with the hard X-ray flux, suggests that the inner accretion disk is the possible emission region of the iron fluorescence line.

Although rotating neutron stars (NSs) have been regarded as being textbook examples of astrophysical particle acceleration sites for decades, details of the acceleration mechanism remain a mystery; for example, we cannot yet observationally distinguish "polar cap" models from "outer gap" models. To solve the model degeneracy, it is useful to study similar systems with much different physical parameters. Strongly magnetized white dwarfs (WDs) are ideal for this purpose, because they have essentially the same system geometry as NSs, but differ largely from NSs in the system parameters, including the size, magnetic field, and the rotation velocity, with the induced electric field expected to reach 10(13)-10(14) eV. Based on this idea, the best candidate among WDs, AE Aquarii, was observed with the fifth Japaneses X-ray satellite, Suzaku. The hard X-ray detector (HXD) on-board Suzaku has the highest sensitivity in the hard X-ray band over 10 keV. A marginal detection in the hard X-ray band was achieved with the HXD, and was separated from the thermal emission. The flux corresponds to about 0.02% of its spin-down energy. If the signal is real, this observation must be a first case of the detection of non-thermal emission from WDs. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region. (C) 2007 Published by Elsevier Ltd on behalf of COSPAR.

The transient X-ray binary pulsar A0535+262 was observed with Suzaku on 2005 September 14 when the source was in the declining phase of the August-September minor outburst. The similar to 103 s X-ray pulse profile was strongly energy dependent, with a double-peaked profile in the soft X-ray energy band (< 3 keV) and a single-peaked smooth profile in hard X-rays. The width of the primary dip is found to increase with energy. The broadband energy spectrum of the pulsar is well described with a negative and positive power law with exponential (NPEX) continuum model, along with a blackbody component for soft excess. A weak iron K alpha emission line with an equivalent width similar to 25 eV was detected in the source spectrum. The blackbody component is found to be pulsating over the pulse phase, implying that the accretion column and/or the inner edge of the accretion disk may be the possible emission site of the soft excess in A0535+262. The higher value of the column density is believed to be the cause of the secondary dip in the soft X-ray energy band. The iron line equivalent width is found to be constant (within errors) over the pulse phase. However, a sinusoidal type of flux variation of the iron emission line, in phase with the hard X-ray flux, suggests that the inner accretion disk is the possible emission region of the iron fluorescence line.

Although rotating neutron stars (NSs) have been regarded as being textbook examples of astrophysical particle acceleration sites for decades, details of the acceleration mechanism remain a mystery; for example, we cannot yet observationally distinguish "polar cap" models from "outer gap" models. To solve the model degeneracy, it is useful to study similar systems with much different physical parameters. Strongly magnetized white dwarfs (WDs) are ideal for this purpose, because they have essentially the same system geometry as NSs, but differ largely from NSs in the system parameters, including the size, magnetic field, and the rotation velocity, with the induced electric field expected to reach 10(13)-10(14) eV. Based on this idea, the best candidate among WDs, AE Aquarii, was observed with the fifth Japaneses X-ray satellite, Suzaku. The hard X-ray detector (HXD) on-board Suzaku has the highest sensitivity in the hard X-ray band over 10 keV. A marginal detection in the hard X-ray band was achieved with the HXD, and was separated from the thermal emission. The flux corresponds to about 0.02% of its spin-down energy. If the signal is real, this observation must be a first case of the detection of non-thermal emission from WDs. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region. (C) 2007 Published by Elsevier Ltd on behalf of COSPAR.

Suzaku is the fifth in the series of Japanese astronomy satellites devoted to observations of celestial X-ray sources launched on a Japanese M-V rocket on July 10, 2005. Suzaku features the excellent X-ray sensitivity, with high throughput over a broad-band energy range of 0.2 to 600 keV. Suzaku's broad bandpass, low background, and good CCD resolution makes it a unique tool capable of addressing a variety of outstanding problems in astrophysics. Copyright © 2007 by World Scientific Publishing Co. Pvt. Ltd.

Since the typical magnetic field strengths of neutron stars reach 1012 Gauss, the cyclotron resonance produced by a transition between Landau levels appears in the X-ray band. Systematic measurements of cyclotron absorption features in bright sources have been carried out extensively with Ginga, RXTE, BeppoSAX, and INTEGRAL. The cyclotron resonance phenomena can now be studied with a higher sensitivity over a wider hard X-ray band than before, thanks to the Hard X-ray Detector onboard the fifth Japanese X-ray satellite, Suzaku, launched in July, 2005. Suzaku observed Hercules X-1 mainly for calibration purposes, and successfully confirmed its well-known cyclotron absorption feature. Furthermore, the transient pulsar A0535+262 was observed with Suzaku on 14 September, 2005, in the decay phase of its minor outburst (Finger, M.F. Renewed Activity from A0535+26. The Astronomer's Telegram, vol. 595, 2005). The cyclotron resonance of A0535+262 was successfully detected in absorption at about 45 keV (Inoue, H., Kunieda, H., White, N., Kelley, R., Nlihara, T., Terada, Y., Takahashi, H., Kokubun, M., Makishima, K. Suzaku detection of cyclotron line near 50 keV for A0535+26. The Astronomer's Telegram vol. 595, 2005; Terada, Y., Mihara, T., Nakajima, M., et al. Cyclotron resonance energies at a low X-ray luminosity: A0535+262 observed with Suzaku. ApJL 648, L139-LI42, 2006), even though the object was as dim as 30 mCrab at 20 keV. Compared with previous measurements of the same feature achieved at much brighter phases (e.g., Kretschmar, P., Kreykenbohm, I., Pottschmidt, et al. Integral observes possible cyclotron line at 47 keV for 1A0535+262. The Astronomer's Telegram, vol. 601, 2005; Wilson, C.A., Finger, M.H. RXTE confirms cyclotron line near 50 keV for A0535+26. The Astronomer's Telegram 605, 2005), the Suzaku results give a new constraint to luminosity-related changes in the resonance energy that are observed in other binary pulsars (Nakajima, M., Mihara, T., Makishima, K., Niko, H. A further study of the luminosity-dependent cyclotron resonance energies of the binary X-ray pulsar 4U 0115+63 with the Rossi X-ray timing explorer. ApJ 646, 1125-1138, 2006). (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Since the typical magnetic field strengths of neutron stars reach 1012 Gauss, the cyclotron resonance produced by a transition between Landau levels appears in the X-ray band. Systematic measurements of cyclotron absorption features in bright sources have been carried out extensively with Ginga, RXTE, BeppoSAX, and INTEGRAL. The cyclotron resonance phenomena can now be studied with a higher sensitivity over a wider hard X-ray band than before, thanks to the Hard X-ray Detector onboard the fifth Japanese X-ray satellite, Suzaku, launched in July, 2005. Suzaku observed Hercules X-1 mainly for calibration purposes, and successfully confirmed its well-known cyclotron absorption feature. Furthermore, the transient pulsar A0535+262 was observed with Suzaku on 14 September, 2005, in the decay phase of its minor outburst (Finger, M.F. Renewed Activity from A0535+26. The Astronomer's Telegram, vol. 595, 2005). The cyclotron resonance of A0535+262 was successfully detected in absorption at about 45 keV (Inoue, H., Kunieda, H., White, N., Kelley, R., Nlihara, T., Terada, Y., Takahashi, H., Kokubun, M., Makishima, K. Suzaku detection of cyclotron line near 50 keV for A0535+26. The Astronomer's Telegram vol. 595, 2005; Terada, Y., Mihara, T., Nakajima, M., et al. Cyclotron resonance energies at a low X-ray luminosity: A0535+262 observed with Suzaku. ApJL 648, L139-LI42, 2006), even though the object was as dim as 30 mCrab at 20 keV. Compared with previous measurements of the same feature achieved at much brighter phases (e.g., Kretschmar, P., Kreykenbohm, I., Pottschmidt, et al. Integral observes possible cyclotron line at 47 keV for 1A0535+262. The Astronomer's Telegram, vol. 601, 2005; Wilson, C.A., Finger, M.H. RXTE confirms cyclotron line near 50 keV for A0535+26. The Astronomer's Telegram 605, 2005), the Suzaku results give a new constraint to luminosity-related changes in the resonance energy that are observed in other binary pulsars (Nakajima, M., Mihara, T., Makishima, K., Niko, H. A further study of the luminosity-dependent cyclotron resonance energies of the binary X-ray pulsar 4U 0115+63 with the Rossi X-ray timing explorer. ApJ 646, 1125-1138, 2006). (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Suzaku deep observations have discovered two highly significant nonthermal X-ray sources, Suzaku J1804-2142 (Src 1) and Suzaku J1804-2140 (Src 2), positionally coincident with the unidentified TeV gamma-ray source, HESS J1804-216. The X-ray sources are not time variable and show no Counterpart in other wavebands, except for the TeV source. Src 1 is unresolved at Suzaku spatial resolution, whereas Src 2 is extended or composed of multiple sources. The X-ray spectra are highly absorbed, hard, and featureless, and are well fitted by absorbed power-law models with best-fit photon indices and absorption columns of -0.3(-0.5)(+0.5) and 0.2(-0.2)(+2.0) x 10(22) cm(-2) for Src 1, and 1.7(-1.0)(+1.4) and 1.1(-0.6)(+1.0) x 10(23) cm(-2) for Src 2. The measured X-ray absorption to the latter source is signif icantly larger than the total Galactic neutral hydrogen column in that direction. The unabsorbed 2-10 keV band luminosities are 7.5 x 10(32) (d/5 kpc)(2) erg s(-1) (Src 1) and 1.3 x 10(33) (d/5 kpc)(2) erg s(-1) (Src 2), where d is the source distance. Among the handful of TeV sources with known X-ray counterparts, HESS J1804-216 has the largest ratio of TeV gamma-ray to hard X-ray fluxes. We discuss the nature of the emission and propose the Suzaku sources as plausible counterparts to the TeV source, although further observations are necessary to confirm this.

We have been developed Si/CdTe semiconductor Compton telescope to explore the universe in the energy band from several 10 keV to a few MeV. In our Si/CdTe Compton telescope, a stacked thin CdTe pixel detector is a key component to achieve higher detection efficiency for MeV gamma-rays maintaining high energy resolution. In this paper, results from a prototype stacked CdTe pixel detector are reported, which consists of three layers of CdTe pixel detectors and one CdTe pixel detector at their side. With this prototype detector, we succeeded in Compton reconstruction of images and spectra in the energy band 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.