RXTE Observations of 1A 1744−361: Correlated Spectral and Timing Behavior

Abstract

We analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the transient low-mass X-ray binary (LMXB) system 1A 1744-361. We explore the X-ray intensity and spectral evolution of the source, perform timing analysis, and find that 1A 1744-361 shows ``atoll'' behavior during the outbursts. The color-color diagram indicates that this LMXB was observed in a low-intensity, spectrally hard (low-hard) state and in a high-intensity ``banana'' state. The low-hard state shows a horizontal pattern in the color-color diagram, and the previously reported ``dipper QPO'' appears only during this state. We also perform energy spectral analyses, and report the first detection of a broad iron emission line and an iron absorption edge from 1A 1744-361.