2007ApJ...660.1386W

The X-ray variability of the microquasar XTE J1550-564 is studied with time-domain techniques using data from an RXTE PCA observation on 1998 September 8. The 2-60 keV average shot profile is obtained by superposing shots with 1 ms time binning after aligning their peaks. The spectral behavior during the averaged shot exhibits prominent differences from that previously observed in Cyg X-1. The 13-60 keV/2-13 keV and 16-60 keV/13-16 keV hardness ratios during a shot are lower and higher, respectively, than those for steady emission. The correlation coefficients between intensity and 13-60 keV/2-13 keV and 16-60 keV/13-16 keV hardness ratios are also negative and positive, respectively. These results indicate that the physical processes at work in the low state of XTE J1550-564 may be different from those in Cyg X-1.