The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by the combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit background based on a combination of new techniques, including the concept of a well-type active shield counter. With an effective area of $142 \,\mathrm{cm}^{2}$ at 20 keV and $273 \,\mathrm{cm}^{2}$ at 150 keV, the background level at sea level reached $\sim 1 \times 10^{-5} \,\mathrm{cts} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2} \,\mathrm{keV}^{-1}$ at 30 keV for the PIN diodes, and $\sim 2 \times 10^{-5} \,\mathrm{cts} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2} \,\mathrm{keV}^{-1}$ at 100 keV, and $\sim 7 \times 10^{-6} \,\mathrm{cts} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2} \,\mathrm{keV}^{-1}$ at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of $\sim 4 \,\mathrm{cm}$ thick BGO crystals, have a large effective area for sub-MeV to MeV $\gamma$-rays. They work as an excellent $\gamma$-ray burst monitor with limited angular resolution ($\sim 5^{\circ}$). The on-board signal-processing system and the data transmitted to the ground are also described.
Using Chandra, extended X-ray emission was detected from the direction of 6 globular clusters: 47 Tucanae, NGC 6752, M 5, $\omega$ Centauri, M 80, and NGC 6266. These X-ray sources, extending to a few arcmin, are located $1'-6'$ away from the cluster centers, and some are found in the direction of cluster motion through the Galactic halo. All of these sources are concluded to be diffuse, rather than an assembly of faint discrete X-ray sources. Those in 47 Tuc and NGC 6752 have similar spectra, described by a power law with a photon index of $\sim 2$, or a thin-thermal model with a temperature of $\sim 3 \!-\!4$ keV. Furthermore, they both have 843 MHz radio counterparts. The diffuse emission from $\omega$ Cen exhibits a $\sim 1.0$ keV thermal spectrum, while that from M 5 shows an even softer ($\sim$ 0.05 keV) spectrum. While the diffuse source in $\omega$ Cen could be a background contaminant, the others are likely to be physically associated with the globular clusters. Then, the absorption-corrected 0.5–4.5 keV luminosity of the sources in 47 Tuc and NGC 6752 becomes $(3\!-\!6)\times 10^{32}$ erg s$^{-1}$. These results are discussed in the context of shocks produced by the cluster motion through the Galactic halo, and the associated gas heating and particle acceleration.
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