The rationale for a semipermanent all-sky X-ray monitor and a variety of options for its implementation are discussed. It is concluded that the Space Station offers an excellent opportunity for hosting such a monitor, and that a set of pinhole cameras can be configured to provide an effective and economical monitor system. A baseline of six independent pinhole modules, each of which requires approximately 1 cu ft, 30 pounds, 2 W and 100 bits per second, can provide full sky coverage with scientifically interesting sensitivities. No other resources or special accommodation (such as detailed alignment registration, time-tagging, or on-orbit servicing) would be required. The baseline system can locate bright sources to a few arcmin and can simultaneously measure each of the several hundred sources in the sky brighter than a few thousandths the intensity of the Crab nebula every day for decades.

All-sky monitors for X-ray astronomy

?????We present near-infrared (observed frame) spectra of the high-redshift quasar S4 0636+68 at z = 3.2, which was previously thought to be one of a group of strong Fe II emitters [i.e., F(Fe II ??4434?4684)/F(H?) > 1]. Our K-band spectrum clearly shows emission lines of H? and [O III] ??4959, 5007, as well as optical Fe II emission. Our computed value of F(Fe II ??4434?4684)/F(H?) 0.8 for S4 0636+68 is less than previously thought and, in fact, is comparable to values found for radio-loud, flat-spectrum, low-z quasars. Therefore S4 0636+68 appears not to be a strong optical Fe II emitter. Although more than half () of the high-z quasars observed to date are still classified as strong optical Fe II emitters, their Fe II/H? ratios, for the most part, follow the same trend as do those of low-z quasars, i.e., an anticorrelation in EW(Fe II)/EW(H?) versus EW([O III])/EW(H?), with radio-loud quasars having a mean value of EW(Fe II)/EW(H?) approximately half that of radio-quiet quasars at comparable values of EW([O III])/EW(H?).

M. S. Wilkerson

Papers

The spectrum of the quasar B2 1225+31.