Detection Of Quasi-periodic Oscillation Research Articles

Detection of quasi-periodic oscillation in the optical light curve of the blazar S5 0716+714

Detection of quasi-periodic oscillation in the optical light curve of the blazar S5 0716+714

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

Abstract In this work, we explore the long-term variability properties of the blazar PKS 0219−164 in the radio and the γ-ray regime, utilizing the OVRO 15 GHz and the Fermi/LAT observations from the period 2008–2017. We found that γ-ray emission is more variable than the radio emission implying that γ-ray emission possibly originated in more compact regions while the radio emission represented continuum emission from the large-scale jets. Also, in the γ-ray, the source exhibited spectral variability, characterized by the softer-when-brighter trend, a less frequently observed feature in the high-energy emission by BL Lacs. In radio, using Lomb–Scargle periodogram and weighted wavelet z-transform, we detected a strong signal of quasi-periodic oscillation (QPO) with a periodicity of 270 ± 26 days with possible harmonics of 550 ± 42 and 1150 ± 157 day periods. At a time when detections of QPOs in blazars are still under debate, the observed QPO with high statistical significance (∼97%–99% global significance over underlying red-noise processes) and persistent over nearly 10 oscillations could make one of the strongest cases for the detection of QPOs in blazar light curves. We discuss various blazar models that might lead to the γ-ray and radio variability, QPO, and the achromatic behavior seen in the high-energy emission from the source.

Detection of the first infra-red quasi-periodic oscillation in a black hole X-ray binary

We present analysis of fast variability of Very Large Telescope/ISAAC (infra-red), \textit{XMM-Newton}/OM (optical) and EPIC-pn (X-ray), and RXTE/PCA (X-ray) observations of the black hole X-ray binary GX 339-4 in a rising hard state of its outburst in 2010. We report the first detection of a Quasi Periodic Oscillation (QPO) in the infra-red band (IR) of a black hole X-ray binary. The QPO is detected at 0.08 Hz in the IR as well as two optical bands (U and V). Interestingly, these QPOs are at half the X-ray QPO frequency at 0.16 Hz, which is classified as the type-C QPO; a weak sub-harmonic close to the IR and optical QPO frequency is also detected in X-rays. The broad band sub-second time scale variability is strongly correlated in IR/X-ray bands, with X-rays leading the IR by over 100 ms. This short time delay, shape of the cross correlation function and spectral energy distribution strongly indicate that this broad band variable IR emission is the synchrotron emission from the jet. A jet origin for the IR QPO is strongly favoured, but cannot be definitively established with the current data. The spectral energy distribution indicates a thermal disc origin for the bulk of the optical emission, but the origin of the optical QPO is unclear. We discuss our findings in the context of the existing models proposed to explain the origin of variability.

Constraints on Torque‐reversing Accretion‐powered X‐Ray Pulsars

The observed abrupt torque reversals in X-ray pulsars, 4U 1626-67, GX 1+4, and OAO 1657—415, can be explained by a transition in accretion-flow rotation from Keplerian to sub-Keplerian, which takes place at a critical accretion rate, ~1016-1017gs-1. When a pulsar system spins up near equilibrium spin before the transition, the system goes into spin-down after transition to sub-Keplerian. If a system is well into the spin-up regime, the transition can cause a sharp decrease in spin-up rate but not a sudden spin-down. These observable types of abrupt torque change are distinguished from the smooth torque variation caused by a change of in the Keplerian flow. The observed abrupt torque reversal is expected when the pulsar magnetic field B* ~5 × 1011b−1/2p L P1/2*,10 G, where the magnetic pitch parameter bp is of the order of a few, Lx,36 is the X-ray luminosity in 1036 ergs s-1, and P*,10 is the pulsar spin period in 10 s. Observed quasi-periodic oscillation (QPO) periods tightly constrain the model. For 4U 1626-67, ≈ 2.7 × 1016 g s-1 with b1/2p B* ≈ 2 × 1012 G. We estimate ~6 × 1016 g s-1 and b1/2p B* ~5 × 1013 G for GX 1+4, and ~1 × 1017 g s-1 and b1/2p B* ~2 × 1013G for OAO 1657-415. Reliable detection of QPOs before and after torque reversal could directly test the model. We discuss some outstanding uncertainties and difficulties in the present model.