相关论文: Possible ~0.4 hour X-ray quasi-periodicity from an…

We discuss methods to compute significance levels for the existence of quasi-periodic oscillations (QPOs) in Active Galactic Nuclei (AGN) which take the red-noise character of the X-ray lightcurves of these objects into account. Applying…

Binary systems with a neutron-star primary accreting from a companion star display variability in the X-ray band on time scales ranging from years to milliseconds. With frequencies of up to ~1300 Hz, the kilohertz quasi-periodic…

RE J1034+396 is one of the most extreme Narrow-line Seyfert 1s detected thus far, showing the only quasi-periodic oscillation (QPO) reliably detected in an Active Galactic Nucleus (AGN). Comparison with similar spectral and timing…

Long-standing optical quasi-periodic oscillations (QPOs) with periodicity of hundreds to thousands of days have been accepted as indicators for central sub-pc binary black hole systems (BBHs) in broad line active galactic nuclei (BLAGN).…

We report the discovery of X-ray quasi-periodic oscillations (QPOs) at frequencies of 3-4 mHz from a transient ultraluminous X-ray source (ULX) X42.3+59 in M82. The QPOs are strong and broad and appear with weak or absent red noise, and are…

Very low frequency ({\nu} ~ 1.9 mHz) quasi-periodic oscillations (QPO) have been detected in 2 - 60 keV X-rays from 4U1700-37 using auto-correlation function analysis of RXTE archival data. No pulsar signal was detected in the data. Less…

The black hole X-ray binary GX\,339-4 showed an X-ray outburst during 2021. The {\it AstroSat} captured this outburst when the source entered into the intermediate flux state while the count rate was declining. The source showed an…

The high time resolution and large area of the Rossi X-ray Timing Explorer have been essential in the detection and characterization of high-frequency quasi-periodic variability in the flux from neutron stars in low-mass X-ray binaries. An…

We present the discovery of a low-frequency $\approx 5.7$ Hz quasi-periodic oscillation (QPO) feature in observations of the black hole X-ray binary MAXI J1535-571 in its soft-intermediate state, obtained in September-October 2017 by the…

We report the detection of type-B quasi-periodic oscillation (QPO) of the black hole X-ray binary Swift J1728.9-3613 observed by NICER during the 2019 outburst. A type- B QPO was observed for the first two days and it disappeared as flux…

The active galactic nucleus (AGN) RE J1034+396 displays the most significant X-ray Quasi-Periodic Oscillation (QPO) detected so far. We perform a detailed spectral-timing analysis of our recent simultaneous XMM-Newton, NuSTAR and Swift…

In the narrow-line Seyfert 1 galaxy 1H 0707-495, recently a transient quasi-periodic oscillation (QPO) signal with a frequency of $\sim 2.6\times 10^{-4}$ Hz has been detected at a high statistical significance. Here, we reanalyze the same…

The X-ray emission from active galactic nuclei (AGN) is believed to come from a combination of inverse Compton scattering of photons from the accretion disk and reprocessing of the direct X-ray emission by reflection. We present hard (10-80…

We report the discovery of a $\sim 1.5 \times 10^{-4}$ Hz ($\sim 2$ hr) X-ray quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a $\sim 70$ ks XMM-Newton observation. The QPO is significantly detected ($\sim 3.3…

We analyze the 11-year long-term light curve of the Radio-loud Narrow-line Seyfert 1 (NLSy1) galaxy J0849+5108 and the nearly simultaneous $\gamma$-ray data of the source. The data were obtained with the Owens Valley Radio Observatory 40-m…

Using data obtained in 1994 June/July with the Extreme Ultraviolet Explorer deep survey photometer and in 2001 January with the Chandra X-ray Observatory Low Energy Transmission Grating Spectrograph, we investigate the extreme-ultraviolet…

HETE J1900.1--2455 is a peculiar accreting millisecond X-ray pulsar (AMXP) because it has shown intermittent pulsations after 22 days from the beginning of its outburst. The origin of intermittent pulses in accreting systems remains to be…

The OVRO 40-m telescope has been monitoring the 15 GHz radio flux density of over 1200 blazars since 2008. The 15 GHz light curve of the flat spectrum radio quasar J1359+4011 shows a strong and persistent quasi-periodic oscillation. The…

We present a detailed analysis of the evolution of type-C quasiperiodic oscillations (QPOs) observed during the flaring state of the recently discovered black hole X-ray binary Swift J1727.8-1613, utilizing data from the Insight Hard X-ray…

Time-domain analysis of an archival XMM-Newton observation unveiled a very unusual variability pattern in the soft X-ray emission of PSR J1311-3430, a black widow millisecond pulsar in a tight binary (P_B=93.8 min) with a very low-mass…