The XIS is an X-ray Imaging Spectrometer system, consisting of state-of-the-art charge-coupled devices (CCDs) optimized for X-ray detection, camera bodies, and control electronics. Four sets of XIS sensors are placed at the focal planes of the grazing-incidence, nested thin-foil mirrors (XRT: X-Ray Telescope) onboard the Suzaku satellite. Three of the XIS sensors have front-illuminated CCDs, while the other has a back-illuminated CCD. Coupled with the XRT, the energy range of 0.2-12 keV with energy resolution of 130 eV at 5.9 keV, and a field of view of 18 × 18 are realized. Since the Suzaku launch on 2005 July 10, the XIS has been functioning well.

High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.

Abstract. The ASCA satellite made a quick followup observation of GRB 970828 and detected its fading X-ray afterglow at the position localized by the All-Sky Monitor on the Rossi XTE satellite. Because of the quickness, the afterglow was still rather bright (∼ 4 10 −13 ergs cm −2 s −1 : 2 − 10 keV), and ASCA obtained the data of good quality. We found the spectral features of the absorption which implies a column density of 4.1 10 21 cm −2 at z = 0, together with an emission line at ∼ 5 keV. The line could be red shifted Fe K α line. Hence, it suggests a relatively small red shift z ≈ 0.33 for this GRB.

The variability observed in many complex gamma-ray bursts (GRBs) is inconsistent with causally connected variations in a single, symmetric, relativistic shell interacting with the ambient material ("external shocks"). Rather, either the central site must produce ∼ 10 50 erg s −1 for hundreds of seconds ("internal shocks") or the local spherical symmetry of the shell must be broken on an angular scale much smaller than Γ −1 where Γ is the bulk Lorentz factor for the shell. The observed variability in the external shock models arises from the number of causally connected regions that (randomly) become active. We define the "surface filling factor" to be the ratio of the area of causally connected regions that become active to the observable area of the shell. From the observed variability in 52 BATSE bursts, we estimate the surface filling factor to be typically ∼ 5 × 10 −3 although some values are near unity. We find that the surface filling factor, f , is ∼ 0.1∆T /T in both the constant Γ phase (which probably produces the GRB) and the deaccelerating phase (which probably produces the x-ray afterglows). Here, ∆T is a typical time scale of variability and T is the time since the initial signal. We analyze the 2 hr flare seen by ASCA 36 hr after the GRB and conclude that the surface filling factor must be small (10 −3 ) in the x-ray afterglow phase as well. Compared to the energy required for an isotropic shell, E iso , explanations for low surface filling factor can either require more energy (f −1 E iso ∼ 10 56 erg) or less energy (( ∆T 4T ) 2 E iso ∼ 10 49 erg). Thus, the low filling factor cannot be used as a strong argument that GRBs must be internal shocks.

A gamma-ray burst of 28 August 1997 was localized by the All-Sky Monitor on the Rossi XTE satellite and its coordinates were promptly disseminated. An ASCA followup started 1.17 days after the burst as a Target of Opportunity Observation and detected an X-ray afterglow. The spectral data displayed a hump around ∼ 5 keV and an absorption column of 7.1 × 10 21 cm −2 . This hump structure is likely a recombination edge of iron in the vicinity of the source, taking account of the redshift z = 0.9578 found for the likely host galaxy of the associated radio flare. Radiative Recombination edge and Continuum model can interpret the spectrum from highly ionized plasma in a non equilibrium ionization state. The absorption could be also due to the medium presumably in the vicinity of the GRB.