Quasi-periodic Flux Variations Research Articles

Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 0614+091

We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary 4U 0614+091. This source shows quasiperiodic flux variations on the timescale of ∼days. We use reflection modeling techniques to study various components of the accretion system as the flux varies. We find that the flux of the reflected emission and the thermal components representing the disk and the compact object trend closely with the overall flux. However, the flux of the power-law component representing the illuminating X-ray corona scales in the opposite direction, increasing as the total flux decreases. During the lowest flux observation, we see evidence of accretion disk truncation from roughly 6 gravitational radii to 11.5 gravitational radii. This is potentially analogous to the truncation seen in black hole low-mass X-ray binaries, which tends to occur during the low/hard state at sufficiently low Eddington ratios.

Correlations between the peak flux density and the position angle of inner-jet in three blazars

We aim to investigate the relation between the long-term flux density and the position angle (PA) evolution of inner-jet in blazars. We have carried out the elliptic Gaussian model-fit to the `core' of 50 blazars from 15 GHz VLBA data, and analyzed the variability properties of three blazars from the model-fit results. Diverse correlations between the long-term peak flux density and the PA evolution of the major axis of the `core' have been found in $\sim$ 20% of the 50 sources. Of them, three typical blazars have been analyzed, which also show quasi-periodic flux variations of a few years (T). The correlation between the peak flux density and the PA of inner-jet is positive for S5~0716+714, and negative for S4~1807+698. The two sources cannot be explained with the ballistic jet models, the non-ballistic models have been analyzed to explain the two sub-luminal blazars. A correlation between the peak flux density and the PA (with a T/4 time lag) of inner-jet is found in [HB89]~1823+568, this correlation can be explained with a ballistic precession jet model. All the explanations are based mainly on the geometric beaming effect; physical flux density variations from the jet base would be considered for more complicated situations in future, which could account for the no or less significance of the correlation between the peak flux density and the PA of inner-jet in the majority blazars of our sample.

The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733

We present photometry of HD 189733 during eight transits of its close-in giant planet, and out-of-transit photometry spanning two years. Using the transit photometry, we determine the stellar and planetary radii and the photometric ephemeris. Outside of transits, there are quasiperiodic flux variations with a 13.4 day period that we attribute to stellar rotation. In combination with previous results, we derive upper limits on the orbital eccentricity, and on the true angle between the stellar rotation axis and planetary orbit (as opposed to the angle between the projections of those axes on the sky).

Global Response of Martian Plasma Environment to an Interplanetary Structure: From Ena and Plasma Observations at Mars

As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board the Mars Express satellite. The “subsolar ENA jet“ is generated by the interaction between the solar wind and the Martian exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485 of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic flux variations of the ENA flux at the spacecraft location.

Using Pulsars to Detect Massive Black Hole Binaries via Gravitational Radiation: Sagittarius A* and Nearby Galaxies

Pulsar timing measurements can be used to detect gravitational radiation from massive black hole binaries. The ~106 day quasi-periodic flux variations in Sagittarius A* (Sgr A*) at radio wavelengths reported by Zhao, Bower, & Goss may be due to binarity of the massive black hole that is presumed to be responsible for the radio emission. A 106 day equal-mass binary black hole is unlikely based on its short inspiral lifetime and other arguments. Nevertheless the reported quasi-periodicity has led us to consider whether the long-wavelength gravitational waves from a conjectured binary might be detected in present or future precision timing of millisecond pulsars. While present timing cannot reach the level expected for an equal-mass binary, we estimate that future efforts could. This inquiry has led us to further consider the detection of binarity in the massive black holes now being found in nearby galaxies. For orbital periods of ~2000 day where the pulsar timing measurements are most precise, we place upper limits on the mass ratio of binaries as small as 0.06.

VLBA Observations of GRS 1915+105

AbstractDuring quasi-periodic flux variations, the core of this galactic superluminal source shows: (a) a flat radio spectrum between 13cm and 2cm; (b) elongation of the core along the axis of arcsecond-scale ejecta; (c) a time-delay of ~4 mins at 3.6cm, relative to 2cm; (d) progressively less variation of the flux at 2cm, 3.6cm & 13cm; and (e) scatter-broadening to 1.9mas at 8.4GHz (135mas at 1GHz).

Transient quasi-periodic oscillations in in the X-ray flux of Cygnus X-3

Cygnus X-3, a bright X-ray source at a distance1 of more than ∼12 kpc beyond the edge of the galactic plane, has peculiar properties including very strong radio outbursts2, possibly showing jet-like features3, and emission in various γ-ray bands4–6 (but see ref. 7). The discovery of its 4.8-h X-ray period8 showed that the source is probably a compact (∼1011 cm) binary system, but its nature and that of its companion, the mode of energy generation (accretion or Crab-like pulsar) and also the cause of the X-ray modulation are still uncertain. We describe here X-ray data on Cyg X-3, obtained with EXOSAT, showing transient quasi-periodic oscillations with amplitudes between 5 and 20% of the 1–10-keV flux and periods in the range 50–1,500 s. The oscillations persisted typically for 5–40 (quasi-oscillation) cycles, occurred exclusively in the phase interval 0.0–0.75 (rising branch and top of the X-ray light curve), were seen during the high state and probably also during the low state of the source, and, at least once, were observed with two different periods simultaneously. We suggest that the quasi-periodic flux variations are caused by quasi-periodic phenomena in an accretion disk which partially occults the X-ray source. This tentative interpretation is in accordance with the idea9 that the 4.8-h modulation of the X-ray flux in Cyg X-3 arises by partial occultations of the X-ray source by an accretion disk, like in low-mass X-ray binaries such as 4U1822–37.