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Galactic Black Hole Transient H1743-322 in transition to the hard state

ATEL # 2112; E. Kalemci (Sabanci Un.), J. A. Tomsick (UC Berkeley), S. Corbel (CEA Saclay & Université Paris Diderot), P. Kaaret and F. Grise (Un. of Iowa), S. Migliari (ESAC)
on 7 Jul 2009; 23:06 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Emrah Kalemci (

Subjects: Radio, Infra-Red, Optical, X-ray, Gamma Ray, Request for Observations, Black Holes, Transients

Galactic black hole transient H1743-322 has been in outburst since UT 2009 May 26, (ATELs #2058, #2062). The RXTE PCA count rate has been dropping since 2009 June 23. We have analyzed the PCA data taken between 2009 June 26 and July 7. Quick fits to all sets with a power law + diskbb + smedge model were performed. While the flux was decreasing steadily, the spectral index stayed between 2.2 and 2.1 until 2009 July 4. During these observations only weak timing noise was observed.

On 2009 July 7, the photon index dropped to 1.84 and clear timing features appeared in the power spectrum with a QPO at 3.42 Hz and an overall rms amplitude of 16.5%.

Based on these results, the source is about to, or has already transited to the hard state, and radio and Optical/Infrared activity are expected, and multi-wavelength observations are encouraged.

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R. E. Rutledge , Editor
ATEL Mirror v1.0 Updates