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MAXI/GSC observes Cyg X-3 in a soft-high state

ATEL # 2635; N. Kawai, M. Morii, K. Sugimori (Tokyo Tech), T. Mihara, Y.E. Nakagawa, M. Sugizaki, M. Suzuki, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), K. Kawasaki, S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), A. Yoshida, K. Yamaoka, S. Nakahira (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, M. Nakajima H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.), A. Uzawa, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team:
on 25 May 2010; 15:52 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Nobuyuki Kawai (

Subjects: X-ray, Binaries, Black Holes, Transients
Referred to by ATEL #: 2644, 2646

MAXI/GSC has confirmed that Cyg X-3 is in its soft-high state. The latest X-ray fluxes (daily average, Crab unit) in the three energy bands are shown below. The fluxes in the low state are shown for comparison.

    Date   MJD      2-4 keV     4-10 keV      10-20 keV   ------------------------------------------------------   May 22 55338  0.23 +-0.01  0.38 +-0.01  0.08 +-0.02   May 23 55339  0.24 +-0.01  0.40 +-0.01  0.01 +-0.03   ------------------------------------------------------   Apr 14 55300  0.05 +-0.01  0.14 +-0.01  0.19 +-0.03  (low state)   ------------------------------------------------------   
The current soft X-ray flux is comparable to that in the previous high state in 2009 September, and is about twice as high as the intermediate maxima in 2010 February reported in ATel #2404. Cyg X-3 has not been observed with MAXI/GSC in the last three weeks because it was either located in the sky region covered by the detectors currently powered off due to HV breakdown troubles, or, in the orbital pole. Cyg X-3 became temporarily visible to MAXI due to the special attitude of the ISS for the shuttle docking. The ISS is now back in the normal attitude, and Cyg X-3 is unobservable again for the next several days until the unobservable region moves away from Cyg X-3 by the precession of the ISS orbit.

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R. E. Rutledge , Editor
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