Discovery of a low-frequency broad quasi-periodic oscillation peak in the power density spectrum of Cygnus X-1 with Granat/SIGMA

Details Discovery of a low-frequency broad quasi-periodic oscillation peak in the power density spectrum of Cygnus X-1 with Granat/SIGMA Discovery of a low-frequency broad quasi-periodic oscillation peak in the power density spectrum of Cygnus X-1 with Granat/SIGMA

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...424..395v&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 424, no. 1, p. 395-400

Astronomy and Astrophysics

Astronomy

39

Cygnus Constellation, Radiant Flux Density, Stellar Oscillations, Black Holes (Astronomy), X Ray Astronomy

Scientific paper

A transient broad (delta(f)/f = 0.8 approximately 1) very low frequency (approximately 0.04-0.07 Hz) and strong (fractional rms variations are at the level of approximately 10-15% of total source intensity) quasi-periodic oscillations (QPO) feature was discovered by the SIGMA telescope onboard the Granat observatory in the power density spectra of Cygnus X-1; the source was during all the observations carried out in 1990-1992 in its standard (low or hard) spectral state (Sunyaev & Truemper 1979) with average 40-150 keV flux, corresponding appproximately to the 'nominal' gamma2 level of the source (Ling et al. 1979). The power density spectra, obtained in the 4 x 10-4-10 Hz frequency range, typically exhibit strong very low frequency noise below a few millihertz increasing toward lower frequencies, a nearly flat region from a few millihertz up to a break frequency fbr = 0.04 approximately 0.1 Hz and a power-law spectrum as f-1 above the break frequency. The QPO feature, when observed, was centered below or near the break frequency fbr.

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