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RXTE observes a transition to the low-hard state in H1743-322

ATel #2857; Nikolai Shaposhnikov (UMD/CRESST/GSFC)
on 22 Sep 2010; 19:12 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Nikolai Shaposhnikov (nikolai.v.shaposhnikov@nasa.gov)

Subjects: X-ray, Request for Observations, Black Hole, Transient

Referred to by ATel #: 3263

The galactic black hole candidate H1743-322 has been in the high soft state since the rise state transition in late August 2010 (Atel #2797). Recent observations of H 1743-322 with RXTE/PCA showed the spectral and variability evolution consistent with the source being in a decay transition from the high soft state back to the low hard state. Beginning on September 16, 2010 10:02 UT the source lightcurve showed quasi-periodic oscillations (QPOs) slowing down from 7 Hz during that observation to 1 Hz during the latest observation on September 21, 2010 13:56 UT. Corresponding energy spectrum evolution is marked by hardening of the power law component from the photon index of 2.1 down to 1.6 and an increase of the Comptonized fraction from 0.25 to 0.85 as inferred from modeling the PCU2 spectra with the absorbed Comptonization model (wabs*bmc). The above evolution pattern is consistent with the source evolving through the decay intermediate state. Final transition to the low-hard state is expected within few days. RXTE will continue to monitor the source on a daily basis throughout the decay. Observations at radio and other wavelenghts are strongly encouraged.