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State Transition of the Black Hole Candidate 4U 1543-47

ATel #103; E. Kalemci, J. Tomsick, R. Rothschild (CASS/UCSD), S. Corbel (CEA Saclay), P. Kaaret (CfA), J. McClintock (Harvard)
on 26 Jul 2002; 19:58 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Emrah Kalemci (emrahk@mamacass.ucsd.edu)

Subjects: X-ray, Request for Observations, Binary, Black Hole, Transient

An analysis of Rossi X-ray Timing Explorer pointed observations of the black hole transient 4U 1543-475 (see ATEL#98 and IAUC# 7920 ) indicates that the source is currently in transition, possibly to the low hard state. The X-ray spectra of two observations taken on July 23 and July 24 show a multicolor disk component with ~0.4 keV inner disk temperature and a power law with a photon index of ~2.65. The 2-15 keV band power spectrum has an rms amplitude of ~20%, with a QPO at ~9 Hz and its harmonic at ~18 Hz. The rms amplitude of the QPO is ~6%. The QPO frequency did not move between observations. Further evolution of the temporal and spectral parameters of the source was seen for observations taken on July 25 and July 26. The power law index hardened to ~2.1, and the disk temperature decreased. This was accompanied by an increase in the overall rms amplitude of variability to ~30%, and a decrease in QPO frequency to 5.6 Hz. RXTE All-Sky Monitor hardness ratios indicate that the transition began on July 21 or July 22. We will continue to monitor the source with RXTE, and we encourage observations in the optical and radio bands.