Radio andγ-Ray Variability in the BL Lac PKS 0219−164: Detection of Quasi-periodic Oscillations in the Radio Light Curve

We have studied the first extreme ultraviolet spectroscopic data and a high accuracy light curve for the BL Lac object PKS 2155–304 observed with the Extreme Ultraviolet Explorer (EUVE) on July 21–22, 1992. This target was observed with the Deep Survey Spectrometer telescope for approximateley 30,000 sec during the in-orbit-calibration phase of the mission, allowing to obtain simultaneous image and spectrum.

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Quasi-Periodic and Periodic Oscillations in the Dwarf Nova AH Her

International Astronomical Union Colloquium ◽

10.1017/s0252921100076284 ◽

1979 ◽

Vol 53 ◽

pp. 403-403

Author(s):

J.G. Duthie ◽

R.S. McMillan

Keyword(s):

Light Curve ◽

Autocorrelation Function ◽

High Speed ◽

Statistical Significance ◽

Cataclysmic Variables ◽

Power Spectra ◽

Photometric System ◽

Periodic Oscillations ◽

Dwarf Nova ◽

High Statistical Significance

With a high speed photometric system we have made extensive observation of the dwarf nova AH Her. We have detected rapid oscillations on two consecutive nights during the recovery portion of the light curve of a typical outburst during the spring of 1979. The periods and the sense of the change of period are consistent with previous observations of rapid oscillations of AH Her. On another occasion we detected quasi-periodic oscillations during the rising portion of an outburst. These are similar in appearance to quasi-periodic oscillations found in other cataclysmic variables in that they appear with high statistical significance in the autocorrelation function but are not apparent in power spectra (Robinson and Nather 1979). However they are different from those reported by Robinson and Nather in the sense that they have the same order of period as the periodic rapid oscillations typical of AH Her. These results will be presented together with a discussion of their Implications.

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Probing the X-ray Variability of X-ray Binaries

Symposium - International Astronomical Union ◽

10.1017/s0074180900194483 ◽

2003 ◽

Vol 214 ◽

pp. 236-239

Author(s):

Wenfei Yu

Keyword(s):

Neutron Star ◽

Light Curve ◽

Time Scale ◽

Accretion Rate ◽

Power Spectra ◽

The Other ◽

Periodic Oscillations ◽

X Ray ◽

Orbital Frequency ◽

X Ray Binaries

Kilohertz quasi-periodic oscillations (kHz QPOs) has been regarded as representing the Keplerian frequency at the inner disk edge in the neutron star X-ray binaries. The so-called “parallel tracks” on the plot of the kHz QPO frequency vs. X-ray flux in neutron star X-ray binaries, on the other hand, show the correlation between the kHz QPO frequency and the X-ray flux on time scales from hours to days. This is suspected as caused by the variations of the mass accretion rate through the accretion disk surrounding the neutron star. We show here that by comparing the correlation between the kHz QPO frequency and the X-ray count rate on a certain QPO time scale observed approximately simultaneous in the Fourier power spectra of the X-ray light curve, we have found evidences that the X-ray flux of millihertz QPOs in neutron star X-ray binaries is generated inside the inner disk edge if adopting that the kilohertz QPO frequency is an orbital frequency at the inner disk edge.

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