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H 1743-322 approaching state transition

ATel #2792; T. M. Belloni, T. Muñoz-Darias, S. Motta, H. Stiele, D. Carbone (INAF - Osservatorio Astronomico di Brera)
on 16 Aug 2010; 13:23 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 #: 2797, 3263

After the four RXTE observations reported in ATel #2788, the spectrum of the black-hole binary H 1743-322 softened progressively, while at the same time the characteristic frequencies of its fast time variability increased. This indicated that the system had entered the hard intermediate state and was probably heading to a state transition to the soft intermediate state. This transition is usually associated to (although not coincident with) the ejection of relativistic jets. We report that the latest RXTE observation, on 2010 August 16 01:08-01:37 UT, found the system much softer (hardness of 0.56, see webpage for the HID). A fit with an absorbed power law and a Gaussian emission line at 6.4 keV is not satisfactory and an additional thermal disk system (at an inner temperature of 0.9 keV) is necessary. The total 2-10 keV unabsorbed flux is 3.4e-9 erg cm^-2 s^-1, with a power-law fraction of 0.75. The power law slope is 2.16 +/- 0.03. The power density spectrum shows that the low-frequency QPO has increased to ~5 Hz and the total fractional rms variability dropped to 19%. Comparing to the previous outbursts, we conclude that a transition to the soft intermediate state could take place within the next couple of days, although we remark that in 2008 no such transition took place (see Capitanio et al. 2009, MNRAS, 398, 1194; Motta et al. 2010, arXiv:1006.4773). The next RXTE observations are currently scheduled for Aug. 17 3:36UT and 22:51UT. Observations at longer wavelengths are encouraged.

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