MAXI J1543-564 is probably a black hole candidate evolving through the hard intermediate state

ATel #3341; T. Munoz-Darias, S. Motta, H. Stiele, T. Belloni (INAF - Brera Observatory)
on 12 May 2011; 09:47 UT
Credential Certification: Teo Muñoz-Darias (tmd@brera.inaf.it)

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We report on the last three RXTE observations of the new X-ray transient MAXI J1543-564 (ATEL #3330, #3331, #3334, #3336). Observations were taken between MJD 55691.089 and MJD 55693.066. We find that the evolution of the spectral and timing properties is consistent with MAXI J1543-564 being a black hole candidate in hard intermediate state (i.e., in transition from Hard to Soft states). We fit the energy spectra (3-40 keV) of the source using a power-law component. We see photon index steeping from ~1.9 to ~2.3. Consistent with this, a continuous decrease in hardness (PCA channels 7-13 (2.87-5.71 keV)/14-23 (5.71-9.51 keV)) from 0.8 to 0.64 is observed. As reported in ATel #3334, a quasi periodic oscillation (QPO) is observed in the power density spectra (PDS). QPO frequency increases monotonically from ~1 to ~3 Hz. We identify this feature as a type C QPO. Strong aperiodic variability is also observed in the PDS, with fractional rms decreasing from 29% to 25%. The above properties are consistent with those observed in black hole transients during the hard-to-soft transition. Multi-wavelength observations are strongly encouraged.