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ATEL # 2391; N. Shaposhnikov (U. Maryland & NASA/GSFC)
on 20 Jan 2010; 18:20 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Jean Swank (email@example.com)
Subjects: X-ray, Binaries, Black Holes, Transients
Referred to by ATEL #: 2396, 2424
The first pointed RXTE observation of a new Galactic black hole candidate XTE J1752-223 (Atel #2258) after a two month period of invisibility due to Sun constrains showed that the source has changed its spectral state from a long stable extreme hard state (Atel #2269). Both thermal and a power-law component are present in the energy spectrum. The photon index of the non-thermal part is 1.9. The variability shows a broad band-limited noise with a break at 0.5 Hz accompanied by a strong low frequency quasi-periodic oscillation (QPO) at 2.2 Hz. This picture is consistent with the hard intermediate spectral state of black hole binaries, confirming the anticipated hard-to-soft transition lately indicated by Swift and MAXI data (Atel #2387). RXTE monitoring will continue daily to follow the source evolution. Radio observations to look for a possible ejection event, as well as observations at other wavelengths, are highly recommended.