Optical Quasi-periodic Oscillations Research Articles

A Possible Optical Quasiperiodic Oscillation of 134 days in the Radio-loud Narrow-line Seyfert 1 Galaxy TXS 1206+549 at z = 1.34

Here we report an optical quasiperiodic oscillation (QPO) with a period of ∼134 days detected in g- and r-band light curves of the narrow-line Seyfert 1 galaxy TXS 1206+549 at a redshift of 1.34 with data from observations at the Zwicky Transient Facility (ZTF). After considering the trial factor, the significance levels in the two bands are 3.1σ and 2.6σ, respectively. The QPO signal presents about 10 cycles ranging from 2018 March to 2021 December, thus lasting ∼4 yr. A nearly sinusoidal profile also appears in the folded light curves by using a phase-resolved analysis. Interestingly, in the simultaneous light curve with the timescale of ZTF observations, a potential periodic signal with a similar period is detected in the o-band light curve from Asteroid Terrestrial-impact Last Alert System data; additionally, a weak peak is also detected at a similar period in the γ-ray light curve obtained from Fermi Gamma-ray Space Telescope data. Some potential origins of periodicities in active galactic nuclei are discussed for the QPO reported here.

Optical quasi-periodic oscillations in the TESS light curves of three blazars

ABSTRACT We report the time series analysis of Transiting Exoplanet Survey Satellite light curves of three blazars, BL Lacertae (BL Lac), 1RXS J111741.0+254858, and 1RXS J004519.6+212735, obtained using a customized approach for extracting active galactic nucleus light curves. We find tentative evidence for quasi-periodic oscillations (QPOs) in these light curves that range from 2 to 6 d. Two methods of analysis are used for assessing their significance: generalized Lomb–Scargle periodograms and weighted wavelet Z-transforms. The different approaches of these methods together ensure a robust measurement of the significance of the claimed periodicities. We can attribute the apparent QPOs to the kink instability model, which postulates that the observed QPOs are related to the temporal growth of kinks in the magnetized relativistic jet. We confirm the application of this model to BL Lac and extend the kink instability model to the other two BL Lac objects.

A sub-pc BBH system in SDSS J1609+1756 through optical QPOs in ZTF light curves

ABSTRACT Optical quasi-periodic oscillations (QPOs) are the most preferred signs of sub-pc binary black hole (BBH) systems in active galactic nucleus (AGN). In this manuscript, robust optical QPOs are reported in quasar SDSS J1609+1756 at z = 0.347. In order to detect reliable optical QPOs, four different methods are applied to analyse the 4.45 yr-long Zwicky Transient Facility (ZTF) g/r/i-band light curves of SDSS J1609+1756, direct fitting results by sine function, generalized Lomb–Scargle periodogram, autocross correlation function, and weighted wavelet Z-transform method. The four different methods can lead to well determined reliable optical QPOs with periodicities ∼340 d with confidence levels higher than 5σ, to guarantee the robustness of the optical QPOs in SDSS J1609+1756. Meanwhile, based on simulated light curves through continuous autoregressive process to trace intrinsic AGN activities, confidence level higher than 3σ can be confirmed that the optical QPOs are not misdetected in intrinsic AGN activities, reconfirming the robust optical QPOs and strongly indicating a central sub-pc BBH system in SDSS J1609+1756. Furthermore, based on apparent redshifted shoulders in broad Balmer emission lines in SDSS J1609+1756, space separation of the expected central BBH system can be estimated to be smaller than 107 ± 60 light-days, accepted upper limit of total BH mass ∼(1.03 ± 0.22) × 108 M⊙. Therefore, to detect and report BBH system expected optical QPOs with periodicities around 1 yr is efficiently practicable through ZTF light curves, and combining with peculiar broad-line emission features, further clues should be given on space separations of BBH systems in broad-line AGN in the near future.

A 3.8 yr optical quasi-periodic oscillations in blue quasar SDSS J132144+033055 through combined light curves from CSS and ZTF

ABSTRACT In the manuscript, a 3.8 yr optical quasi-periodic oscillations (QPOs) is reported in blue quasar SDSS J132144+033055 (= SDSS J1321) at z = 0.269, based on 16.3yr-long light curve from both CSS and ZTF directly described by a sinusoidal function. The 3.8 yr QPOs can be confirmed through the Generalized Lomb–Scargle periodogram with confidence level higher than 5σ, through properties of the phase-folded light curve and the WWZ technique. Moreover, the collected Pan-STARRS light curves well follow the sinusoidal function described best fitting results to the Catalina Sky Survey (CSS) and Catalina Sky Survey (ZTF) light curves. The optical QPOs strongly indicate a central binary black hole (BBH) system in SDSS J1321, with expected space separation smaller than 0.018 pc, through the estimated upper limit of total BH mass 3.3 × 109 M⊙ through the correlation between BH mass and continuum luminosity. Meanwhile, we check disc precession applied to explain the optical QPOs. However, under the disc precession assumption, the determined optical emission regions from central BH have sizes about 37RG similar as the sizes 35RG of the expected NUV emission regions through the correlation between disc size and BH mass, indicating the disc precession is not preferred. And due to undetected radio emissions, jet precession can be ruled out. Furthermore, only 0.1 per cent probability can determined as the QPOs mis-detected through CAR process randomly created light curves related to intrinsic AGN activities, re-confirming the optical QPOs with significance level higher than 3σ. Therefore, combining long-term light curves from CSS and ZTF can lead to more QPOs candidates in the near future.

About 300 days Optical Quasi-periodic Oscillations in the Long-term Light Curves of the Blazar PKS 2155-304

Based on the long-term light curves collected from the Catalina Sky Survey (CSS) (from 2005 to 2013) and the All-Sky Automated Survey for Supernovae (ASAS-SN) (from 2014 to 2018), optical quasi-periodic oscillations (QPOs) about 300 days can be well determined in the well-known blazar PKS 2155-304 through four different methods: the generalized Lomb-Scargle periodogram (GLSP) method, the weighted wavelet Z-transform technique, the epoch-folded method and the redfit method. The GLSP determined significance level for the periodicity is higher than 99.9999% based on a false alarm probability. The redfit provided confidence level for the periodicity is higher than 99% in the ASAS-SN light curve, after considering the effects of red noise. Based on continuous autoregressive process created artificial light curves, the probability of detecting fake QPOs is lower than 0.8%. The determined optical periodicity of 300 days from the CSS and ASAS-SN light curves is well consistent with the reported optical periodicity in the literature. Moreover, three possible models are discussed to explain the optical QPOs in PKS 2155-304: the relativistic frame-dragging effect, the binary black hole model and the jet precession model.

A 6.4-yr optical quasi-periodic oscillations in SDSS J075217.84+193542.2: a new candidate for central binary black hole system

ABSTRACT In this manuscript, a 6.4-yr optical quasi-periodic oscillations (QPOs) is detected in the quasar SDSS J075217.84+193542.2 (=+SDSS J0752) at a redshift 0.117, of which 13.6-yr-long light curve from Catalina Sky Survey and All-Sky Automated Survey for Supernovae is directly described by a sinusoidal function with a periodicity 6.4 yr. The 6.4-yr QPOs can be further confirmed through the generalized Lomb–Scargle periodogram with confidence level higher than 99.99 per cent, and through the autocorrelation analysis results, and through the weighted wavelet z-transformation technique. The optical QPOs strongly indicate a central binary black hole (BBH) system in SDSS J0752. The determined two broad Gaussian components in the broad H α can lead to the BBH system with expected space separation about 0.02 pc between the expected two central BHs with determined virial BH masses about 8.8 × 107 and 1.04 × 109 M⊙. Meanwhile, we check the disc precessions applied to explain the optical QPOs. However, under the disc precession assumption, the determined optical emission regions from central BH have sizes about 40RG two times smaller than sizes of the expected Near UltraViolet (NUV) emission regions through the correlation between disc size and BH mass, indicating the disc precessions are not preferred. And due to the lower radio loudness around 0.28, jet precessions can be also totally ruled out. Furthermore, only 0.08 per cent probability can determined as the QPOs misdetected through light curves randomly created by the continuous autoregressive process, reconfirming the reported optical QPOs.

Synchronous X-ray/optical quasi-periodic oscillations from the black hole LMXB MAXI J1820+070

ABSTRACT We present high-speed optical photometry from SAAO and SALT on the black hole LMXB MAXI J1820+070 (ASSASN-18ey), some of it simultaneous with NICER, Swift, and Insight-HXMT X-ray coverage. We detect optical quasi-periodic oscillations (QPOs) that move to higher frequencies as the outburst progresses, tracking both the frequency and evolution of similar X-ray QPOs previously reported. Correlated X-ray/optical data reveal a complex pattern of lags, including an anticorrelation and a sub-second lag that evolve over the first few weeks of outburst. They also show correlated components separated by a lag equal to the QPO period roughly centered on zero lag, implying that the inter-band variability is strongly and consistently affected by these QPOs at a constant phase lag of roughly ±π. The synchronization of X-ray and optical QPOs indicates that they must be produced in regions physically very close to each other; we, thus, propose that they can be explained by a precessing jet model, based on analogies with V404 Cyg and MAXI J1348−630.

New approach to the broad-line-region radius in Mrk142 after considering potential short-term optical transient quasi-periodic oscillations

ABSTRACT Mrk142 is known as the only outlier in R-L space (the correlation between BLR (broad-line region) radii and continuum luminosity) among the low-redshift local reverberation-mapped broad-line active galactic nuclei (BLAGNs) with moderate accretion rates, as its BLR radius is smaller than the expected R-L value. Here, by considering probable optical transient quasi-periodic oscillations (QPOs), a new approach to assessing the BLR radius is presented. Reliable transient QPOs in high-energy emissions from the vicinity of the black hole have been reported in several normal AGNs; however, to date there are few short-term, low-energy optical transient QPOs in normal BLAGNs (i.e. not the QPOs reported in blazars or in AGNs harbouring binary black hole systems). Using the photometric optical light curves, which are well described directly by sinusoidal functions, we report probable short-term optical transient QPOs with periodicities around 14 and 43 d in BLAGN Mrk142, indicating optical QPOs similar to but scaled from those in high-energy bands. By considering the 14-d QPOs related to the reprocessing procedure, a new approach to estimating the BLR radius is possible for Mrk142 through the reverberation mapping technique. The new BLR radius of Mrk142 obeys the R-L relationship well, demonstrating that this relationship is fundamental in local normal BLAGNs without ultra-high accretion rates.

Multiwaveband quasi-periodic oscillation in the blazar 3C 454.3

ABSTRACT We report the detection (>4σ) of a quasi-periodic oscillation (QPO) in the gamma-ray light curve of 3C 454.3 along with a simultaneous marginal QPO detection (>2.4σ) in the optical light curves. Periodic flux modulations were detected in both of these wavebands with a dominant period of ∼47 d. The gamma-ray QPO lasted for over 450 d (from MJD 56800 to 57250), resulting in over nine observed cycles which is among the highest number of periods ever detected in a blazar light curve. The optical light curve was not well sampled for almost half of the gamma-ray QPO span due to the daytime transit of the source, which could explain the lower significance of the optical QPO. Autoregressive Integrated Moving Average (ARIMA) modelling of the light curve revealed a significant, exponentially decaying, trend in the light curve during the QPO, along with the 47 d periodicity. We explore several physical models to explain the origin of this transient quasi-periodic modulation and the overall trend in the observed flux with a month-like period. These scenarios include a binary black hole system, a hotspot orbiting close to the innermost stable circular orbit of the supermassive black hole, and precessing jets. We conclude that the most likely scenario involves a region of enhanced emission moving helically inside a curved jet. The helical motion gives rise to the QPO and the curvature (∼0.05○ pc−1) of the jet is responsible for the observed trend in the light curve.

A Relativistic Orbit Model for Temporal Properties of AGN

We present a unified model for X-ray quasi-periodic oscillations (QPOs) seen in Narrow-line Seyfert 1 (NLSy1) galaxies, γ-ray and optical band QPOs that are seen in Blazars. The origin of these QPOs is attributed to the plasma motion in corona or jets of these AGN. In the case of X-ray QPOs, we applied the general relativistic precession model for the two simultaneous QPOs seen in NLSy1 1H 0707-945 and deduce orbital parameters, such the radius of the emission region, and spin parameter a for a circular orbit; we obtained the Carter’s constant Q, a, and the radius in the case of a spherical orbit solution. In other cases where only one X-ray QPO is seen, we localized the orbital parameters for NLSy1 galaxies REJ 1034+396, 2XMM J123103.2+110648, MS 2254.9-3712, Mrk 766, and MCG-06-30-15. By applying the lighthouse model, we found that a kinematic origin of the jet based γ-ray and optical QPOs, in a relativistic MHD framework, is possible. Based on the inbuilt Hamiltonian formulation with a power-law distribution in the orbital energy of the plasma consisting of only circular or spherical trajectories, we show that the resulting Fourier power spectral density (PSD) has a break corresponding to the energy at ISCO. Further, we derive connection formulae between the slopes in the PSD and that of the energy distribution. Overall, given the preliminary but promising results of these relativistic orbit models to match the observed QPO frequencies and PSD at diverse scales in the inner corona and the jet, it motivates us to build detailed models, including a transfer function for the energy spectrum in the corona and relativistic MHD jet models for plasma flow and its polarization properties.

Complex variability of Kepler AGN revealed by recurrence analysis

ABSTRACT The advent of new time domain surveys and the imminent increase in astronomical data expose the shortcomings of traditional time series analysis (such as power spectra analysis) in characterizing the abundantly varied, complex, and stochastic light curves of Active Galactic Nuclei (AGNs). Recent applications of novel methods from non-linear dynamics have shown promise in characterizing higher modes of variability and time-scales in AGN. Recurrence analysis in particular can provide complementary information about characteristic time-scales revealed by other methods, as well as probe the nature of the underlying physics in these objects. Recurrence analysis was developed to study dynamical trajectories in phase space, which can be constructed from 1D time series such as light curves. We apply the methods of recurrence analysis to two optical light curves of Kepler-monitored AGN. We confirm the detection and period of an optical quasi-periodic oscillation in one AGN, and confirm multiple other time-scales recovered from other methods ranging from 5 to 60 d in both objects. We detect regions in the light curves that deviate from regularity, provide evidence of determinism and non-linearity in the mechanisms underlying one light curve (KIC 9650712), and determine realizations of a linear stochastic process describe the dominant variability in the other light curve (Zwicky 229–015). We discuss possible underlying processes driving the dynamics of the light curves and their diverse classes of variability.

Optical Quasi-periodic Oscillation of the BL Lacertae Object S5 0716+714 during the Faint State

Abstract In order to search for the evidence of quasi-periodic oscillation (QPO) in blazars, multicolor optical observations of the BL Lacertae object S5 0716+714 were performed from 2005 to 2012. For I band observations on 2010 March 19 with low variability amplitude and low flux level, the same QPO minutes at the 99% significance level is confirmed by the ZDCF method, Lomb–Scargle method, REDFIT, and fitting sinusoidal curves. The observed QPO is likely to be explained by accretion disk variability. If the observed QPO indicates an innermost stable orbital period from the accretion disk, the QPO ≃ 50 minutes corresponds to a black hole mass of for a non-rotating Schwarzschild black hole and for a maximally rotating Kerr black hole.

A VLT-ULTRACAM study of the fast optical quasi-periodic oscillations in the polar V834 Centauri

Quasi-periodic oscillations (QPOs) of a few seconds have been detected in some polars, the synchronised subclass of cataclysmic systems containing a strongly magnetised white dwarf which accretes matter from a red dwarf companion. The QPOs are thought to be related to instabilities of a shock formed in the accretion column, close to the white dwarf photosphere above the impact region. We present optical observations of the polar V834 Centauri performed with the fast ULTRACAM camera mounted on the ESO-VLT simultaneously in three filters (u′, He ii λ4686, r′) to study these oscillations and characterise their properties along the orbit when the column is seen at different viewing angles. Fast Fourier transforms and wavelet analysis have been performed and the mean frequency, rms amplitude, and coherence of the QPOs are derived; a detailed inspection of individual pulses has also been performed. The observations confirm the probable ubiquity of the QPOs for this source at all epochs when the source is in a high state, with observed mean amplitude of 2.1% (r′), 1.5% (He ii), and 0.6% (u′). The QPOs are present in the r′ filter at all phases of the orbital cycle, with a higher relative amplitude around the maximum of the light curve. They are also detected in the He ii and u′ filters but at a lower level. Trains of oscillations are clearly observed in the r′ light curve and can be mimicked by a superposition of damped sinusoids with various parameters. The QPO energy distribution is comparable to that of the cyclotron flux, consistent for the r′ and He ii filters but requiring a significant dilution in the u′ filter. New 1D hydrodynamical simulations of shock instabilities, adapted to the physical parameters of V834 Cen, can account for the optical QPO amplitude and X-ray upper limit assuming a cross section of the accretion column in the range ~(4 − 5) × 1014 cm2. However, the predicted frequency is larger than the observed one by an order of magnitude. This shortcoming indicates that the QPO generation is more complex than that produced in a homogeneous column and calls for a more realistic 3D treatment of the accretion flow in future modelling.

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.

SALT observation of X-ray pulse reprocessing in 4U 1626−67

We investigate optical reprocessing of X-rays in the LMXB pulsar 4U 1626-67 in its current spin-up phase using observations with Southern African Large Telescope (SALT), near-simultaneous observations with Swift-XRT and non-simultaneous RXTE-PCA observations and present the results of timing analysis. Using SALT observations carried out on 5th and 6th March, 2014, we detect some interesting reprocessing signatures. We detect a weak optical Quasi Periodic Oscillation (QPO) in the power density spectrum on March 5th at 48 mHz with a fractional rms of 3.3% in spite of the fact that source shows no corresponding X-ray QPO in the spin-up phase. In the light curve obtained on March 5th, we detect a coherent pulsation at the spin period of ~7.677 s. A previously known, slightly down-shifted side-band is also detected at 129.92 mHz. The frequency spacing between main pulse and this side-band is different from earlier observations, though the statistical significance of the difference is limited. The light curve of 6th March displays short time-scale variability in the form of flares on timescales of a few minutes. Folded pulse profiles resulting from data of this night show an interesting trend of pulse peak drifting. This drift could be due to i) rapid changes in the reprocessing agent, like orbital motion of an accretion disk warp around the neutron star or ii) intrinsic pulse phase changes in X-rays. We also examine some X-ray light curves obtained with RXTE-PCA during 2008-2010 for pulse shape changes in short time scales during X-ray flares.

Quasi-periodic oscillations in accreting magnetic white dwarfs

Quasi-periodic oscillations (QPOs) are observed in the optical flux of some polars with typical periods of 1 to 3 s but none have been observed yet in X-rays where a significant part of the accreting energy is released. QPOs are expected and predicted from shock oscillations. Most of the polars have been observed by the XMM-Newton satellite. We made use of the homogeneous set of observations of the polars by XMM-Newton to search for the presence of QPOs in the (0.5–10 keV) energy range and to set significant upper limits for the brightest X-ray polars. We extracted high time-resolution X-ray light curves by taking advantage of the 0.07 s resolution of the EPIC-PN camera. Among the 65 polars observed with XMM-Newton from 1998 to 2012, a sample of 24 sources was selected on the basis of their counting rate in the PN instrument to secure significant limits. We searched for QPOs using Fast Fourier Transform (FFT) methods and defined limits of detection using statistical tools. Among the sample surveyed, none shows QPOs at a significant level. Upper limits to the fractional flux in QPOs range from 7% to 71%. These negative results are compared to the detailed theoretical predictions of numerical simulations based on a 2D hydrodynamical code presented in Paper II. Cooling instabilities in the accretion column are expected to produce shock quasi-oscillations with a maximum amplitude reaching ~40% in the bremsstrahlung (0.5–10 keV) X-ray emission and ~20% in the optical cyclotron emission. The absence of X-ray QPOs imposes an upper limit of ~(5–10) g cm-2 s-1 on the specific accretion rate but this condition is found inconsistent with the value required to account for the amplitudes and frequencies of the observed optical QPOs. This contradiction outlines probable shortcomings with the shock instability model.

Reprocessing model for the optical quasi-periodic oscillations in black hole binaries

A number of black hole X-ray transients show quasi-periodic oscillations (QPOs) in the optical (ultraviolet) and X-ray bands at the same frequency, which challenge models for production of radiation at these wavelengths. We propose a model where the optical radiation is modulated by the oscillating X-ray flux resulting in varying irradiation of the outer parts of the accretion disc. The proposed QPO mechanism inevitably takes place in the systems with sufficiently small ratio of the outer disc radius to the QPO period. We show that, unlike in the case of the aperiodic variability, it is not possible to obtain the optical QPO profiles from those observed in the X-rays through the transfer function, because of different X-ray signals seen by the disc and by the observer. We demonstrate that with the increasing QPO frequency, occurring at the rising phase of the X-ray outburst, the rms should be constant for sufficiently low frequencies, then to increase reaching the peak and finally to drop substantially when the QPO period becomes comparable to the light-crossing time to the outer disc. We predict that the QPO rms in this model should increase towards shorter wavelengths and this fact can be used to distinguish it from other QPO mechanisms.

A UNIFIED LENSE-THIRRING PRECESSION MODEL FOR OPTICAL AND X-RAY QUASI-PERIODIC OSCILLATIONS IN BLACK HOLE BINARIES

Recent observations of accreting black holes reveal the presence of quasi-periodic oscillations (QPO) in the optical power density spectra. The corresponding oscillation periods match those found in the X-rays, implying a common origin. Among the numerous suggested X-ray QPO mechanisms, some may also work in the optical. However, their relevance to the broadband -- optical through X-ray -- spectral properties have not been investigated. For the first time, we discuss the QPO mechanism in the context of the self-consistent spectral model. We propose that the QPOs are produced by Lense-Thirring precession of the hot accretion flow, whose outer parts radiate in the optical wavelengths. At the same time, its innermost parts are emitting the X-rays, explaining the observed connection of QPO periods. We predict that the X-ray and optical QPOs should be either in phase or shifted by half a period, depending on the observer position. We investigate the QPO harmonic content and find that the variability amplitudes at the fundamental frequency are larger in the optical, while the X-rays are expected to have strong harmonics. We then discuss the QPO spectral dependence and compare the expectations to the existing data.

Millihertz quasi-periodic optical oscillations in 4U 0614+091

We report the discovery of a 1mHz optical quasi-periodic oscillation (QPO) in the candidate ultracompact low-mass X-ray binary 4U 0614+091. The ultra-low frequency QPO has no X-ray counterpart in contemporaneous RXTE/PCA data and is likely a signature of structure in the accretion disk. The QPO can be reasonably fitted with a single sine wave but with a phase jump part way through the observation, indicating that it is not coherent.We also identify a 48 min modulation, approximately consistent with the suggested orbital period of O'Brien (2005) and Shahbaz et al. (2008). If this is indeed orbital, it supports an identification of 4U 0614+091 as an ultra-compact source.

Coordinated Optical and X‐Ray Observations of the AM Herculis Objects VV Puppis, V834 Centauri, and EF Eridani

ABSTRACTWe obtained coordinated broadband optical photometry and hard X‐ray data on the AM Her objects VV Pup, V834 Cen, and EF Eri. The X‐ray data were obtained using the Proportional Counter Array detectors of the Rossi X‐Ray Timing Explorer, and the optical data were obtained using the 1 m telescope of the Cerro Tololo Inter‐American Observatory. During our observations, VV Pup and V834 Cen were in their high optical luminosity states with average mV∼17 and 15.1, respectively. EF Eri was in a very low state at the time of our observation: mV>17.7. VV Pup and V834 Cen had average 2–10 keV X‐ray fluxes of 1.7 × 10-12 and 2.13 × 10-11 ergs cm−2 s−1, respectively. EF Eri was not detected in X‐rays. The X‐ray spectrum of V834 Cen was adequately modeled using an absorbed bremsstrahlung continuum with a Gaussian emission line. The best‐fit model had continuum temperature kTX = 11.8 ± 1.0 keV and absorption column nH = (1.03 ± 0.39) × 1022 cm−2. The Gaussian emission line had line center energy E = 6.7 ± 0.1 keV and equivalent width EW = 0.64 keV. VV Pup was too faint to produce reliable spectral fits. The 2–10 keV flux for VV Pup quoted above was based on the best‐fit spectral model. Holding kTX fixed in the fitting process yielded roughly the same flux for kTX = 0.5–30 keV.We detected ∼1 Hz optical quasi‐periodic oscillations (QPOs) with amplitude ∼2.2% from VV Pup and ∼1% from V834 Cen. We did not detect optical QPOs over the range 0.2–1 Hz from EF Eri at a 90% confidence upper limit of 4.5%. The QPO properties are consistent with those found in the literature. None of the targets showed X‐ray QPO activity. However, only V834 Cen yielded a meaningful upper limit: ∼14% at the 90% confidence level over 0.2–1.2 Hz.