MAXI J1543-564 is in the soft state

ATel #3355; T. Munoz-Darias, S. Motta, H. Stiele, T. Belloni (INAF - Brera Observatory)
on 17 May 2011; 09:17 UT
Credential Certification: Teo Muñoz-Darias (tmd@brera.inaf.it)

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We report on the last RXTE observation of the new X-ray transient MAXI J1543-564 (ATEL #3330, #3331, #3334, #3336, #3341). Observation was taken on MJD 55698.023 and the energy spectra (3-40 keV) of the source can be fitted using a power-law component with a photon index of ~2.8. A disc component, if present, is at this level of the analysis marginally significant. The power density spectrum (PDS) does not show any quasi-periodic oscillation (QPO) and a very low level of aperiodic variability is present. Indeed, fractional rms (0.1-64 Hz) is consistent with being as low as 1 per cent. These values indicate that the source is in the soft state. The seven RXTE observations performed so far between MJD 55691.089 and MJD 55698.023 show that photon index has steeped monotonically from ~1.9 to ~2.8 and the aperiodic variability has dropped from rms ~ 29% to almost disappear. A strong QPO shifting in frequency from ~1 Hz (see also ATEL #3334) to ~4.5 Hz was observed during the first four observations (until MJD 55694.092). No QPO was present during the fifth observation, with total fractional rms being close to 10%, which usually marks the transition to soft states (Munoz-Darias, Motta & Belloni 2011, MNRAS, 410, 679). Fractional rms was 8% on MJD 55696.65, and a weak QPO feature at 5 Hz, that could be tentatively associated with a type-B QPO, is present in the PDS. Hardness (PCA channels 7-13 (2.87-5.71 keV)/14-23 (5.71-9.51 keV)) has evolved from 0.8 to 0.4, consistent with the changes observed in the photon index and showing that the source has a rather hard energy spectrum even during soft states. As reported in ATEL #3341, the evolution of the spectral and timing behavior of MAXI J1543-564 is similar to that observed in other black hole candidates. Multi-wavelength observations are strongly encouraged.

Light curve and Hardness-Intensity Diagram