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Galactic black hole transient H1743-322 in transition to the hard state

ATEL # 1378; E. Kalemci (Sabanci Univ.), J. A. Tomsick (SSL / UC Berkeley), S. Corbel ((CEA Saclay & Université Paris Diderot) , T. Tzioumis (ATNF)
on 3 Feb 2008; 7:57 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Emrah Kalemci (

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

Galactic black hole transient H1743-322 has been in outburst since Jan 4, 2008 (ATEL #1348, #1349, #1352). We have analyzed the RXTE PCA data taken on Jan 24 and Feb 1st. Quick fits to both data sets with a power law + diskbb + smedge model were performed. On Jan 24, the photon index was 2.3. The ratio of the power law flux to the overall flux in the 3-25 keV band was 70%. The power spectrum showed weak broad band noise with 8% rms amplitude of variability. The source perhaps entered the hard intermediate state at the time.

A radio observation with ATCA on January 28 resulted in no detection with an rms upper limit of 0.15 mJy at 8.6 and 4.8 GHz.

On Feb 1st, the photon index was 1.55, and the power law flux was 90% of the overall flux. The power spectrum showed a QPO at 4.5 Hz, and stronger broad band noise with 15% rms amplitude. Based on these results, the source is about to, or has already transited to the hard state, and radio and OIR activity are expected, and multi-wavelength observations are encouraged.

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