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RXTE observations of the black hole candidate H1743-322 in its rising phase of the outburst

ATel #1780; K. Yamaoka (Aoyama Gakuin University), J. H. Swank (NASA/GSFC), T. Belloni (INAF), and H. Takahashi (Hiroshima University)
on 13 Oct 2008; 01:38 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Kazutaka Yamaoka (yamaoka@phys.aoyama.ac.jp)

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

Referred to by ATel #: 1804, 1829, 3277

A series of RXTE Public ToO observations of the black hole candidate H1743-322 (ATel #1739, #1745, #1779) were performed on Oct. 3, 7, 8, 9 and 11.

The broadband PCA and HEXTE spectra in the 3-200 keV range are well explained by a power-law with a photon index of 1.34-1.44, with a high energy cutoff at 83-94 keV, modified with Galactic absorption and smeared edge at 7.11 keV due to cold iron (instead of reflection component). The PCA absorbed flux in 3-20 keV is gradually increasing from 2.28e-9 erg/cm^2/s (86 mCrab) to 2.50e-9 erg/cm^2/s (94 mCrab), while the HEXTE measured flux in 20-100 keV is decreasing from 3.24e-9 erg/cm^2/s to 2.93e-9 erg/cm2/s, suggesting that the source spectrum is gradually softening. A low-frequency QPO is detected in the PCA power spectrum, with frequency increasing from 0.3 to 0.6 Hz (from Oct 3 to 11) and a clear peak at its first overtone.

The spectral softening and the QPO indicate progression into the hard intermediate state, as suggested by Corbel et al. (ATel #1766). The flux is still very low, by comparison to previous outbursts (See http://lheawww.gsfc.nasa.gov/users/craigm/galscan/html/H1743-322.html ) and the QPO frequencies could rise a lot higher in this state.

Further multi-wavelength observations are strongly encouraged.