An History of Photoionized Gas in AGN

The history of the subject can be divided into several epochs. These are the years prior to 1993 (ie. before the launch of the ASCA), 1993-2000 dominated by the discoveries of ASCA and BeppoSAX, and the dawn of the Grating Era with the launch of Chandra X-ray Observatory (CXO) and XMM-Newton missions in 1999.

Prior to the mid 1990s the study of PIGs in AGN was severely limited by a lack of instruments with sufficient spectral resolution in the correct bandpass. This period covers from the first suggestion by Halpern (1984) of the importance of PIG in at least some AGN (based on observations of the quasar MR2251-178 obtained using the HRI & MPC detectors in the Einstein Observatory), through the EXOSAT era (and support for a PIG interpretation of MR2251-178), the Ginga era (suggesting the existence of Hi-PIG), to the start of the ROSAT operations. [More....]

With the launch of ASCA in 1993 Feb, the study of PIGs in AGN...
incomplete [1993 also saw the 1st servicing mission to HST during which the COSPAR corrective optics were installed] This period covers the launch of Beppo-SAX (in 1996 Apr), the end of ROSAT operations, up to the launch of CXO and XMM-Newton. More....]

The launches of CXO (1999 Jul) and XMM-Newton (1999 Dec) signaled the dawn of the Grating Era. This period covers extends to date, but (unfortunately) also includes the end of ASCA and Beppo-SAX operations. [More....]