ASCA and Ginga observations of GX 1+4

The X-ray binary pulsar GX 1+4 was observed with Ginga every year from 1987 to 1991 and with ASCA in 1994. During the Ginga observations, GX 1+4 was i n the steady spin-down phase, although the X-ray flux was not steady. Assum ing a distance of 10 kpc, the absorption-corrected X-ray luminosity decreas ed down to L2-20 keV = 2.7 x 10(36) ergs s(-1) in 1991, after the peak acti vity of L2-20 keV = 1.2 x 10(37) ergs s(-1) in 1989. On the other hand, the absorption column density showed a drastic increase over the Ginga observa tion series. It was less than 10(23) cm(-2) at the beginning of the series, and it reached a maximum of (1.4 +/- 0.2) x 10(24) cm(-2) in 1991, indicat ing a rapid accumulation of matter in the vicinity of the source. The cente r energy and equivalent width of the iron line were consistent with emissio n by isotropically distributed cold matter. The ASCA observation was perfor med on 1994 September 15, a month before the transition into a spin-up phas e. The source brightened again to L2-20 keV = 10(37) ergs s(-1). The absorp tion column density was observed to decrease for the first time to (2.08 +/ - 0.02) x 10(23) cm(-2). The ionization degree of iron in the absorbing mat ter was determined to be Fe I-Fe IV using the ratio of the line-center ener gy to the absorption-edge energy. The low ionization degree is consistent w ith an absorbing matter distribution extending similar to 10(12) cm from th e source. We compared the results with optical observations and found that the optical data also supports the picture. Based on the geometrical model, possible causes of the bimodal behavior of the source are discussed.