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Astron. Astrophys. 347, L23-L26 (1999)

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Letter to the Editor

The frequency resolved spectroscopy of Cyg X-1: fast variability of the Fe [FORMULA] line

M. Revnivtsev 1,2, M. Gilfanov 2,1 and E. Churazov 2,1

1 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117810 Moscow, Russia,
2 Max-Planck-Institute für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching bei München, Germany

Received 11 May 1999 / Accepted 11 June 1999


We studied the frequency resolved energy spectra of Cyg X-1 during the standard low (hard) spectral state using the data of the Rossi X-Ray Timing Explorer. We found that the relative amplitude of the reflection features - the iron fluorescent line at [FORMULA] keV and the smeared edge above [FORMULA] keV - decreases with the increasing frequency. In particular we found that the equivalent width of the iron line decreases above [FORMULA] Hz and drops twice in value at a frequency of [FORMULA] Hz.

The assumption that such behavior is solely due to a finite light crossing time of the reflecting media, would imply the characteristic size of the reflector [FORMULA] cm, corresponding to [FORMULA] for a [FORMULA] black hole. Alternatively the lack of high frequency oscillations of the reflected component may indicate that the short time scale, [FORMULA] 50-100 msec, variations of the primary continuum appear in the geometrically different, likely inner, part of the accretion flow and give a rise to a significantly weaker, if any, reflected emission than the longer time scale events.

Key words: methods: data analysis – stars: binaries: general – stars: individual: (Cyg X-1) – X-rays: general

Send offprint requests to: revnivtsev@hea.iki.rssi.ru

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© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999