Discovery Of Quasi-periodic Oscillations Research Articles

First discovery of quasi-periodic oscillations in the dwarf nova HS 2325+8205 based on TESS photometry

ABSTRACT HS 2325+8205 is a long-period eclipsing dwarf nova with an orbital period above the period gap (Porb > 3 h) and is reported to be a Z Cam-type dwarf nova. We study the light variation and the quasi-periodic oscillations (QPOs) of HS 2325+8205 based on the photometry of theTransiting Exoplanet Survey Satellite (TESS). Using a continuous wavelet transform, a Lomb–Scargle periodogram (LSP), and sine fitting methods, we find for the first time that there is a QPO of ∼2160 s in the long outburst top light curves of HS 2325+8205. Moreover, we find that the oscillation intensity of the QPOs of HS 2325+8205 is related to the orbital phase, and the intensity in orbital phases 0.5–0.9 is stronger than in orbital phases 0.1–0.5. Therefore, the relationship between the oscillation intensity of QPOs and the orbital phase may become a topic of research into the origin of QPOs. In addition, we use the LSP to correct the orbital period of HS 2325+8205 to 0.19433475(6) d.

QUASI-PERIODIC OSCILLATIONS IN SHORT RECURRING BURSTS OF THE SOFT GAMMA REPEATER J1550–5418

The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. The scarcity of giant flares makes a search for QPOs in the shorter, far more numerous bursts from Soft Gamma Repeaters (SGRs) desirable. In Huppenkothen et al (2013), we developed a Bayesian method for searching for QPOs in short magnetar bursts, taking into account the effects of the complicated burst structure, and have shown its feasibility on a small sample of bursts. Here, we apply the same method to a much larger sample from a burst storm of 286 bursts from SGR J1550-5418. We report a candidate signal at 260 Hz in a search of the individual bursts, which is fairly broad. We also find two QPOs at 93 Hz and one at 127 Hz, when averaging periodograms from a number of bursts in individual triggers, at frequencies close to QPOs previously observed in magnetar giant flares. Finally, for the first time, we explore the overall burst variability in the sample, and report a weak anti-correlation between the power-law index of the broadband model characterising aperiodic burst variability, and the burst duration: shorter bursts have steeper power law indices than longer bursts. This indicates that longer bursts vary over a broader range of time scales, and are not simply longer versions of the short bursts.

QUASI-PERIODIC OSCILLATIONS AND BROADBAND VARIABILITY IN SHORT MAGNETAR BURSTS

The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. However, with only three giant flares ever recorded, and only two with data of sufficient quality to search for QPOs, such analysis is seriously data limited. We set out a procedure for doing QPO searches in the far more numerous, short, less energetic magnetar bursts. The short, transient nature of these bursts requires the implementation of sophisticated statistical techniques to make reliable inferences. Using Bayesian statistics, we model the periodogram as a combination of red noise at low frequencies and white noise at high frequencies, which we show is a conservative approach to the problem. We use empirical models to make inferences about the potential signature of periodic and quasi-periodic oscillations at these frequencies. We compare our method with previously used techniques and find that although it is on the whole more conservative, it is also more reliable in ruling out false positives. We illustrate our Bayesian method by applying it to a sample of 27 bursts from the magnetar SGR J0501+4516 observed by the Fermi Gamma-ray Burst Monitor, and we find no evidence for the presence of QPOs in any of the bursts in the unbinned spectra, but do find a candidate detection in the binned spectra of one burst. However, whether this signal is due to a genuine quasi-periodic process, or can be attributed to unmodeled effects in the noise is at this point a matter of interpretation.

Discovery of a 0.02 Hz QPO feature in the transient X-ray pulsar KS 1947+300

We report the discovery of Quasi Periodic Oscillations (QPO) at 0.02 Hz in a transient high mass X-ray binary pulsar KS 1947+300 using {\em RXTE}-PCA. The QPOs were detected during May-June 2001, at the end of a long outburst. This is the 9th transient accretion powered high magnetic field X-ray pulsar in which QPOs have been detected and the QPO frequency of this source is lowest in this class of sources. The unusual feature of this source is that though the outburst lasted for more than 100 days, the QPOs were detected only during the last few days of the outburst when the X-ray intensity had decayed to 1.6% of the peak intensity. The rms value of the QPO is large, $\sim15.4\pm1.0%$ with a slight positive correlation with energy. The detection of QPOs and strong pulsations at a low luminosity level suggests that the magnetic field strength of the neutron star is not as high as was predicted earlier on the basis of a correlation between the spin-up torque and the X-ray luminosity.

Quasi‐periodic Oscillations in XTE J0111.2−7317: Highest Frequency among the HMXB Pulsars

We report here discovery of Quasi Periodic Oscillations (QPOs) in the High Mass X-ray Binary (HMXB) Pulsar XTE J0111.20-7317 during a transient outburst in this source in December 1998. Using observations made with the proportional counter array of the Rossi X-ray Timing Explorer during the second peak and the declining phase of this outburst we have discovered a QPO feature at a frequency of 1.27 Hz. We have ruled out the possibility that the observed QPOs can instead be from the neighbouring bright X-ray pulsar SMC X-1. This is the highest frequency QPO feature ever detected in any HMXB pulsar. In the absence of a cyclotron absorption feature in the X-ray spectrum, the QPO feature, along with the pulse period and X-ray flux measurement measurement helps us to constrain the magnetic field strength of the neutron star.

Discovery of High-Frequency Quasi-periodic Oscillations in the Black Hole Candidate XTE J1859+226.

We report the discovery of quasi-periodic oscillations (QPOs) at roughly 187 and 150 Hz in the X-ray intensity of X-ray nova XTE J1859+226. The source was observed during a recent outburst with the Rossi X-Ray Timing Explorer. Besides these high-frequency QPOs, we have also detected QPOs (and sometimes their harmonics) at 6-7 Hz and significant broadband variability at low frequencies. These properties, as well as the observed hard X-ray spectrum, make XTE J1859+226 a black hole candidate (BHC). The detection of QPOs at two distinct frequencies greater, similar100 Hz in two observations separated by about 4 hr provide additional insights into the high-frequency QPO phenomenon in BHCs. The importance lies in the proposed interpretations, which invariably involve the effects of strong gravity near a black hole. We compare our results to those of other BHCs and discuss the impact of the observational data on the models in a global context.

Discovery of the quasi-periodic oscillations from V0332+53

The discovery of quasi-periodic oscillations (QPOs) in the X-ray flux from the recurrent transient X-ray pulsar VO332+53 is reported. The centroid frequency, full width at half maximum (FWHM), and the relative root mean square (RMS) amplitude of the QPOs are (5.1 +/- 0.5) x 10<SUP>-2</SUP> Hz, (3.3 +/- 1.5) x 10<SUP>-2</SUP> Hz, and 4.8% +/- 1.2%, respectively. The beat frequency model is tested using these results and previously reported QPOs from other X-ray binary pulsars.

The discovery of 7 and 24-28 hertz quasi-periodic oscillations in the X-ray flux of GX 17 + 2 (4U 1813-14)

view Abstract Citations (18) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Discovery of 7 and 24--28 Hertz Quasi-periodic Oscillations in the X-Ray Flux of GX 17+2 (4U 1812-14) Stella, L. ; Parmar, A. N. ; White, N. E. Abstract The discovery of quasi-periodic oscillations (QPOs) in the X-ray flux of the bright galactic bulge source GX 17 + 2 is reported. The relation between the QPO frequency and the source intensity of GX 17 + 2 is bimodal and is similar to that previously reported from Sco X-1. On August 20-21, 1985, the QPO frequency was about 7 Hz and showed no significant change associated with about 10 percent intensity variations. In another observation 25 days later, the frequency varied between 24 Hz and 28 Hz and was strongly correlated with 5 percent variations in intensity. During an observation on August 3-4, 1983, no QPOs were observed with an upper limit to the rms strength of about 1.4 percent. A search for a possible correlation between the QPOs and spectral properties was carried out by fitting to the spectra the disk plus black-body boundary layer model suggested by White et al. (1986). The QPO frequency was larger when the black-body luminosity was minimum, contrary to that observed from Sco X-1. Publication: The Astrophysical Journal Pub Date: October 1987 DOI: 10.1086/165640 Bibcode: 1987ApJ...321..418S Keywords: Galactic Nuclei; Stellar Oscillations; X Ray Stars; Astronomical Models; Black Body Radiation; Galactic Bulge; Temporal Resolution; Astrophysics; X-RAYS: SOURCES; X-RAYS: BINARIES; STARS: PULSATION full text sources ADS | data products SIMBAD (4)

Bimodal quasi-oscillatory and spectral behavior in Scorpius X-1

X-ray observations were made to follow up the discovery of quasi-periodic oscillations (QPO) in Sco X-1. The QPO is observed in the quiescent state, and between flares in the active state. When the source is quiescent, the QPO frequency is 6 Hz and anticorrelated with intensity; in the active state, the frequency ranges from 10 to 20 Hz and is strongly correlated with intensity. At high intensities the QPO dissolves into continuum noise. The QPO rms amplitude decreases with count rate, and increases with photon energy. There are two modes of spectral behavior, with a one-to-one correspondence to the two modes of QPO: the spectral hardness ratio varies more steeply with intensity when the source shows 6 Hz QPO, than for 10 to 20 Hz QPO. Transitions between QPO modes, which occur when the flux is at its lowest levels, correspond to transitions between hardness ratio modes. The QPO frequency changes continuously through the transitions, which last a few hundred seconds.