... Smale et al. (1994) analyzed the ASCA/GIS data for 4U 1820-30, which was observed in the low state in 1993. ... Results of our long-term study of 4U 1820-30 are presented in detail in the next sections and compared with our previous results for 4U 1728-34 and GX 3+1. 6 http://heasarc ... /grouping 4 The Astrophysical Journal, 767:160 (23pp), 2013 April 20 Titarchuk, Seifina, Frontera Table 4 Best-fit Parameters of Spectral Analysis of PCA and HEXTE/RXTE Observations of 4U 1820-30 in the 3...