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State transition in H 1743-322

ATel #2797; T. M. Belloni, T. Muñoz-Darias, S. Motta, H. Stiele, D. Carbone (INAF - Osservatorio Astronomico di Brera)
on 17 Aug 2010; 14:21 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Tomaso Belloni (belloni@merate.mi.astro.it)

Subjects: X-ray, Binary, Black Hole, Transient

Referred to by ATel #: 2857, 3263

The latest RXTE pointed observation of the black-hole binary H 1743-322 on 2010 August 17 03:23-04:21 UT found the source to have undergone a transition to the soft-intermediate state (SIMS). During the previous observation on 2010 August 16 01:08-01:37 UT reported in ATel #2792 H 1743-322 was in the hard intermediate state. The characteristic feature of the SIMS is the presence of a strong type-B low-frequency QPO in the power-density spectrum. This was observed, although at a much lower frequency than usual. The centroid is 3.57 +/- 0.02 Hz, with a quality factor Q~7. The continuum power is well fitted with a power law with index -1.2. The total 0.1-64 Hz fractional rms is 5.3%, much lower than in the preceding HIMS on the previous day (19%). The spectrum is much softer (hardness ~0.42) and is well fitted with the same model as in the previous observation (absorbed power law, diskbb and gaussian emission line, with absorption fixed at 1.6e22 cm^-2). The power-law index ad inner disk temperature are very similar to those of the previous observation (2.22 +/- 0.02 and 0.98 +/- 0.01 keV respectively). The 2-10 keV unabsorbed flux is higher 5.9e-9 erg cm^-2 s^-1, with a power-law fraction of 0.53, accounting for the softening. The transition was expected on the basis of the general time evolution of black-hole transients and the behavior of H 1743-322 in the previous outbursts (Motta et al. 2010, arXiv:1006.4773).

Light curve and hardness-intensity diagram for the current outburst of H 1743-322