The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10–600 keV, energy resolutions of $\sim 4 \,\mathrm{keV}$ (FWHM) at 40 keV and $\sim 11\%$ at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5–20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15–70 and 150–500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

Using deep Chandra ACIS observation data for Cygnus A, we report evidence of non-thermal Xray emission from radio lobes surrounded by a rich intra-cluster medium (ICM). The diffuse X-ray emission, which are associated with the eastern and western radio lobes, were observed in a 0.7-7 keV Chandra ACIS image. The lobe spectra are reproduced with not only a single-temperature Mekal model, such as that of the surrounding ICM component, but also an additional power-law (PL) model. The X-ray flux densities of PL components for the eastern and western lobes at 1 keV are derived as 77.7 +28.9 −31.9 nJy and 52.4 +42.9 −42.4 nJy, respectively, and the photon indices are 1.69 +0.07 −0.13 and 1.84 +2.90 −0.12 , respectively. The non-thermal component is considered to be produced via the inverse Compton (IC) process, as is often seen in the X-ray emission from radio lobes. From a re-analysis of radio observation data, the multiwavelength spectra strongly suggest that the seed photon source of the IC X-rays includes both cosmic microwave background radiation and synchrotron radiation from the lobes. The derived parameters indicate significant dominance of the electron energy density over the magnetic field energy density in the Cygnus A lobes under the rich ICM environment.

An observation of the West lobe of radio galaxy Fornax A (NGC 1316) with Suzaku is reported. Since Feigelson et al. (1995, ApJ, 449, L149) and Kaneda et al. (1995, ApJ, 453, L13) discovered the cosmic microwave background boosted inverse-Comptonized (IC) X-rays from the radio lobe, the magnetic field and electron energy density in the lobes have been estimated under the assumption that a single component of the relativistic electrons generates both the IC X-rays and the synchrotron radio emission. However, electrons generating the observed IC X-rays in the 1–10 keV band do not possess sufficient energy to radiate the observed synchrotron radio emission under the estimated magnetic field of a few $\mu$G. On the basis of observations made with Suzaku, we show in the present paper that a 0.7–20 keV spectrum is well described by a single power-law model with an energy index of 0.68 and a flux density of 0.12$\pm$0.01 nJy at 1 keV from the West lobe. The derived multiwavelength spectrum strongly suggests that a single electron energy distribution over a Lorentz factor $\gamma$$=$ 300–90000 is responsible for generating both the X-ray and radio emissions. The derived physical quantities are not only consistent with those reported for the West lobe, but are also in very good agreement with those reported for the East lobe.

We present the results of X-ray observations of the well-studied TeV blazar Mrk 421 with the Suzaku satellite in 2006 April 28. During the observation, Mrk 421 was undergoing a large flare and the X-ray flux was variable, decreasing by ∼ 50 %, from 7.8 × 10 −10 to 3.7 × 10 −10 erg s −1 cm −2 in about 6 hours, followed by an increase by ∼ 35 %. Thanks to the broad bandpass coupled with high-sensitivity of Suzaku, we measured the evolution of the spectrum over the 0.4-60 keV band in data segments as short as ∼ 1 ksec. The data show deviations from a simple power law model, but also a clear spectral variability. The time-resolved spectra are fitted by a synchrotron model, where the observed spectrum is due to a exponentially cutoff power law distribution of electrons radiating in uniform magnetic field; this model is preferred over a broken power law. As another scenario, we separate the spectrum into "steady" and "variable" components by subtracting the spectrum in the lowest-flux period from those of other data segments. In this context, the difference ("variable") spectra are all well described by a broken power law model with photon index Γ ∼ 1.6, breaking at energy ǫ brk ≃ 3 keV to another photon index Γ ∼ 2.1 above the break energy, differing from each other only by normalization, while the spectrum of the "steady" component is best described by the synchrotron model. We suggest the rapidly variable component is due to relatively localized shock (Fermi I) acceleration, while the slowly variable ("steady") component is due to the superposition of shocks located at larger distance along the jet, or due to other acceleration process, such as the stochastic acceleration on magnetic turbulence (Fermi II) in the more extended region.

Suzaku observations of the blazar OJ 287 were performed in 2007 April 10 -13 and November 7 -9. They correspond to a quiescent and a flaring state, respectively. The X-ray spectra of the source can be well described with single power-law models in both exposures. The derived X-ray photon index and the flux density at 1 keV were found to be Γ = 1.65 ± 0.02 and S 1keV = 215 ± 5 nJy, in the quiescent state. In the flaring state, the source exhibited a harder X-ray spectrum (Γ = 1.50 ± 0.01) with a nearly doubled X-ray flux density S 1keV = 404 +6 −5 nJy. Moreover, significant hard X-ray signals were detected up to ∼ 27 keV. In cooperation with the Suzaku, simultaneous radio, optical, and very-high-energy γ-ray observations of OJ 287 were performed with the Nobeyama Millimeter Array, the KANATA telescope, and the MAGIC telescope, respectively. The radio and optical fluxes in the flaring state (3.04 ± 0.46 Jy and 8.93 ± 0.05 mJy at 86.75 Hz and in the V -band, respectively) were found to be higher by a factor of 2 -3 than those in the quiescent state (1.73 ±0.26 Jy and 3.03 ± 0.01 mJy at 86.75 Hz and in the V -band, respectively) . No notable γ-ray events were detected in either observation. The spectral energy distribution of OJ 287 indicated that the X-ray spectrum was dominated by inverse Compton radiation in both observations, while synchrotron radiation exhibited a spectral cutoff around the optical frequency. Furthermore, no significant difference in the synchrotron cutoff frequency was found between the quiescent and flaring states. According to a simple synchrotron self-Compton model, the change of the spectral energy distribution is due to an increase in the energy density of electrons with small changes of both the magnetic field strength and the maximum Lorentz factor of electrons.