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The RATAN observations of Cygnus X-1

ATel #3546; S. A. Trushkin, N. A. Nizhelskij, G. V. Zhekanis (SAO RAS)
on 11 Aug 2011; 09:55 UT
Credential Certification: Sergei Trushkin (satr@sao.ru)

Subjects: Radio, Optical, X-ray, Binary, Black Hole

Referred to by ATel #: 3616, 7322, 9089, 10459

We carry out monitoring of Cygnus X-1 at 4.8 GHz with the RATAN-600 radio telescope (SAO RAS) from April 2011, when Grinberg et al. (ATEL#3307) have detected softing the X-ray emission. We detected the some increase (from ~15 mJy to ~25 mJy) of the flux density at 4.8 GHz during last five days that could be connected with the possible hard-to-soft state transition reported by Negoro et al (ATEL #3534). But Pooley (ATEL#3535) reported about decrease of the recent fluxes at 15 GHz. Thus probably the current mean radio spectrum of Cyg X-1 became steeper. The light curve of Cyg X-3 during April-August 2011 measured with RATAN-600 at 4.8 GHz and in ASM with Swift/BAT and XTE are shown in figure: http://www.sao.ru/hq/lran/XB/CygX-1/CygX-1_lc_rad_xray_2011apr-aug.png