Related papers: Wavelets with Ridges: A High-Resolution Representa…
We searched for quasi-periodicities on year-like timescales in the light curves of 6 blazars in the optical - near infrared bands and we made a comparison with the high energy emission. We obtained optical/NIR light curves from REM…
We interpret the correlation over five orders of magnitude between high frequency and low frequency in a quasi-periodic oscillations (QPO) found by Psaltis, Belloni & van der Klis (1999) for black hole (BH), neutron star (NS) systems and…
We have carried out a systematic study of the properties of the kilo-Hertz quasi-periodic oscillations (QPO) observed in the X-ray emission of the neutron star low-mass X-ray binary 4U1608-52, using archival data obtained with the Rossi…
We introduce an algorithm for applying a cross-wavelet transform to analysis of quasiperiodic variations in a time-series, and introduce significance tests for the technique. We apply a continuous wavelet transform and the cross-wavelet…
Quasi-periodic oscillations (QPOs) are very common in black hole accretion systems that are seen from the modulations in luminosity. Many supermassive black hole sources (e.g., RE J1034+396, 1H~0707-495, MCG-6-30-15, 1ES~1927+654,…
Our photometric monitoring revealed that DW Cnc, which was originally classified as a dwarf nova (V=15--17.5), remained at a bright state of Rc=14.68+/-0.07 for 61 days. In conjunction with optical spectra lacking a strong He II emission…
Kepler high cadence data are used to measure the orbital periods and to determine the orbital waveforms of five dwarf novae. A significant improvement of the period of V1504 Cyg is achieved, while for the other systems periods are derived…
Using EUV photometry obtained with the Extreme Ultraviolet Explorer (EUVE) satellite and UBVR optical photometry obtained with the 2.7-m telescope at McDonald Observatory, we have detected quasi-coherent oscillations (so-called ``dwarf nova…
This study presents the detection of a high-frequency quasi-periodic oscillation (QPO) in the Seyfert galaxy NGC 1365 based on observational data obtained by \emph{XMM-Newton} in January 2004. Utilizing the weighted wavelet Z-transform…
In this work, we have searched quasi-periodic oscillations (QPOs) in the 15 GHz light curve of the FSRQ PKS J0805-0111 monitored by the Owens Valley Radio Observatory (OVRO) 40 m telescope during the period from January 9,2008 to May…
We consider the so-called Keplerian periodogram, in which the putative detectable signal is modelled by a highly non-linear Keplerian radial velocity function, appearing in Doppler exoplanetary surveys. We demonstrate that for planets on…
Observations from the Rossi X-Ray Timing Explorer have shown the existence of high frequency quasi-periodic oscillations (HFQPOs) in the X-ray flux from accreting black hole binary systems. In at least two systems, these HFQPOs come in…
Black holes have their proper oscillations, which are called the quasi-normal modes. The proper oscillations of astrophysical black holes can be observed in the nearest future with the help of gravitational wave detectors. Quasi-normal…
Many accreting black holes and neutron stars exhibit rapid variability in their X-ray light curves, termed quasi-periodic oscillations (QPOs). The most commonly observed type is the low-frequency ($\lesssim 10$ Hz), type-C QPO, while only a…
The Galactic black hole (BH) X-ray binary 4U 1630-47 went into a new outburst in 2021 after $\sim$ 600 days from its 2020 outburst. We perform a detailed analysis of quasi-periodic oscillations and spectral evolutions during its 2021…
We investigate spectro-temporal properties for two black hole X-ray binary sources, MAXI J1535$-$571 and H 1743$-$322, during their hard and hard-intermediate states. For MAXI J1535$-$571, we analyze Swift/XRT, NuSTAR and NICER…
In previous papers we proposed a model that high-frequency quasi-periodic oscillations (QPOs) observed in black-hole and neutron-star X-ray binaries are disk oscillations (inertial-acoustic and/or g-mode oscillations) resonantly excited on…
We consider the inner regions of accretion disks surrounding black holes and neutron stars and investigate the nonlinear time dependent evolution of thermal-viscous instabilities. The viscous stress is assumed to be proportional to the gas…
Quasi-periodic oscillations (QPOs) have been discovered in the X-ray emission of many neutron stars and black holes. The QPOs with frequencies greater than about 300 Hz are thought to be produced near the surfaces of neutron stars and the…
Gravitational-wave observatories become more sensitive with each observing run, increasing the number of detected gravitational-wave signals. A limiting factor in identifying these signals is the presence of transient non-Gaussian noise,…