Quasi-periodic Variations Research Articles

CORRIGENDUM

Hydrological ProcessesVolume 36, Issue 6 e14630 CORRIGENDUMFree Access CORRIGENDUM This article corrects the following: Tidal frequencies and quasiperiodic subsurface water level variations dominate redox dynamics in a salt marsh system Emilio Grande, Bhavna Arora, Ate Visser, Maya Montalvo, Anna Braswell, Erin Seybold, Corianne Tatariw, Kathryn Beheshti, Margaret Zimmer, Volume 36Issue 5Hydrological Processes First Published online: May 25, 2022 First published: 12 June 2022 https://doi.org/10.1002/hyp.14630AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In the referenced article, Grande et al. (2022), an additional affiliation for co-author Braswell, A. has been added:-. Florida Sea Grant, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida, USA. REFERENCE Grande, E., Arora, B., Visser, A., Montalvo, M., Braswell, A., Seybold, E., Tatariw, C., Beheshti, K., & Zimmer, M. (2022). Tidal frequencies and quasiperiodic subsurface water level variations dominate redox dynamics in a salt marsh system. Hydrological Processes, 36(5), e14587. https://doi.org/10.1002/hyp.14587Wiley Online LibraryCASWeb of Science®Google Scholar Volume36, Issue6June 2022e14630 ReferencesRelatedInformation

Positive piecewise continuous quasi-periodic solutions to logistic impulsive differential equations

ABSTRACT To prove the existence of piecewise continuous solutions to a logistic quasi-periodic differential system with impulses (whose coefficients have rationally independent periods), this system is divided into a differential equation and a difference equation. The quasi-periodicity of a function is proved by showing that this function is the uniform limit of a series of trigonometric polynomials with a finite total number of frequencies. The asymptotically stable quasi-periodic positive and piecewise continuous solution is proved to exist and to be unique. Quasi-periodic variation of the environment leads to a quasi-periodic growth of the population size in the sense that the rationally independent frequencies of the system are also frequencies of the quasi-periodic solution. The positive solutions have a repeated behavior similar to that of the quasi-periodic solution for a sufficiently long time due to asymptotical stability. The separation of the continuous-discrete system into a differential equation and a difference equation is a method of proving the existence of a quasi-periodic solution with perturbed coefficients of the impulsive system.

Tidal frequencies and quasiperiodic subsurface water level variations dominate redox dynamics in a salt marsh system

AbstractSalt marshes are hotspots of nutrient processing en route to sensitive coastal environments. Whilst our understanding of these systems has improved over the years, we still have limited knowledge of the spatiotemporal variability of critical biogeochemical drivers within salt marshes. Sea‐level rise will continue to force change on salt marsh functioning, highlighting the urgency of filling this knowledge gap. Our study was conducted in a central California estuary experiencing extensive marsh drowning and relative sea‐level rise, making it a model system for such an investigation. Here we instrumented three marsh positions subjected to different degrees of tidal inundation (6.7%, 8.9%, and 11.2% of the time for the upper, middle, and lower marsh positions, respectively), providing locations with varied biogeochemical characteristics and hydrological interactions at the site. We continuously monitored redox potential (Eh) at depths of 0.1, 0.3, and 0.5 m, subsurface water levels (WL), and temperature at 0.7 m depth at each marsh position. To understand how drivers of subsurface biogeochemical processes fluctuate across tidal cycles, we used wavelet analyses to explain the interactions between Eh and WL. We found that tidal forcing significantly affects key drivers of biogeochemical processes by imparting controls on Eh variability, likely driving subsurface hydro‐biogeochemistry of the salt marsh. Wavelet coherence showed that the Eh‐WL relationship is nonlinear, and their lead–lag relationship is variable. We found that precipitation events perturb Eh at depth over timescales of hours, even though WL shows relatively minimal change during events. This work highlights the importance of high frequency in situ measurements, such as Eh, to help explain factors that govern subsurface biogeochemistry and hydrological processes in salt marshes.

Quasi-periodic Oscillation Analysis for the BL Lacertae Object 1823+568

We studied the optical band periodic variability of 1823+568 using the Jurkevich method, the Lomb–Scargle periodogram and the REDFIT38 software, and found evidence of quasi-periodic oscillation. An unprecedented variability with period days was identified by three different analysis methods. This quasi-periodic variability most likely results from nonballistic helical jet motion driven by the orbital motion in a binary black hole system. Considering the light-travel time effect, the real physical period is P d = 67.1 yr. Moreover, we estimated that the primary black hole mass is M ≃ 1.92 × 109 M ⊙ to 3.43 × 109 M ⊙.

GJ 3236: An active red-dwarf eclipsing binary system

GJ 3236 is a low-mass red-dwarf eclipsing binary (EB) with two M4V components. In this paper, new photometric light curves (LCs) of GJ 3236 are presented and analyzed by using the 2013 version of the Wilson–Devinney (W–D) code. Our photometric solutions suggest that GJ 3236 is an active detached EB system with strong magnetic field. Since 2009, we have monitored this target more than 10 years and obtained 22 mid-eclipse times with high precision. By using the O–C method, we revised its period as 0.7712562 days. According to Applegate mechanism, the O–C diagram of GJ 3236 should show a quasi-periodic variation, however, it does not now. Based on these, we thought that it is possible evolved through the accretion of circumstellar matter. Besides, both of components of GJ 3236 present a similar radius inflation, which could be explained by the strong magnetic activity.

Species-dependent solar rotation effects on the Martian ionosphere

ABSTRACT Atmospheric escape is a central issue in understanding how Mars lost the habitability and it is critically controlled by the link between the atmosphere and the interplanetary space, i.e. the ionosphere. The predominant driver of the Martian ionospheric variability is the solar extreme ultraviolet radiation. To date, how the ionospheric electrons respond to this radiation has been well investigated, but the responses of various ion species are to be understood. Based on a multi-instrument data set from the Mars Atmosphere and Volatile Evolution, we report direct observations of quasi-periodical variations of photoelectrons and ions, with a common period of ≈27.2 d and almost in exact phase with the solar rotation. These diverse variations present remarkably different amplitudes. The ion density variation has a much larger amplitude than the solar flux variation and the electron density variation has a smaller amplitude. For comparison, the amplitude of the photoelectron intensity variation is nearly identical to that of the solar flux variation. The species-dependent solar rotation effects provide a good diagnostic of the upper atmospheric and ionospheric chemistry, urging reconsiderations of the solar-driven composition and variability of any planetary ionosphere.

Disturbances in the Ionosphere That Accompanied Typhoon Activity in the Vicinity of China in September 2019

AbstractWe have acquired HF Doppler measurements and studied the dynamics of the ionosphere in the ∼100–300 km altitude range during the 1–10 September 2019 period of typhoon activity near the People's Republic of China (PRC). The multifrequency multiple path system located at the Harbin Engineering University campus, the PRC, and probing the ionosphere at oblique incidence was used to identify the effects from the typhoons. The response of the ionosphere to the Typhoon Lingling was detected along three adjacent radio‐wave propagation paths where chaotic and quasiperiodic variations in the Doppler shift and a significant (from −1 to 1 Hz or greater) Doppler spectrum broadening were observed to occur. The Doppler spectrum chaotic variations are due to plasma turbulence generated by typhoons in the ionosphere, and the Doppler shift quasiperiodic variations along the main ray are due to infrasound and atmospheric gravity waves (AGWs) launched by the typhoons. The relative amplitude of quasiperiodic variations in the electron density in the field of the infrasound wave reached several percent, and in the field of the AGW attained from ten to a few tens of percent. The effects of the Typhoon Faxai during 9/10 and 10/11 September 2019 nights were accompanied by a 27% decrease in the electron density in the ionospheric E and F regions. At the closest approach of the Typhoon Faxai to the ionosonde during 8/9 September 2019 night, when it had the largest energy, a 56% increase was detected in the ionospheric F region electron density.

A Possible 3 yr Quasi-periodic Oscillation in γ-Ray Emission from the FSRQ S5 1044+71

Variability is a typical observation feature of Fermi blazars, which sometimes shows quasi-periodic oscillation (QPO). In this work, we obtain 5 day binned light curves (with a time coverage of ∼12.9 yr) for S5 1044+71, based on Fermi-LAT data; apply five different methods—Date-compensated Discrete Fourier Transform, Jurkevich, Lomb–Scargle Periodogram, a Fortran 90 program, and the Weighted Wavelet Z-transform—to the γ-ray light curve; and find a possible QPO of 3.06 ± 0.43 yr at the significance level of ∼3.6σ. A binary black hole model, including an accretion model and a dual-jet model, is used to explain this quasi-periodic variability. We also estimate the Doppler factors and the apparent velocity for the two jet components. We speculate that this γ-ray quasi-periodic modulation suggests the presence of a binary supermassive black hole in S5 1044+71.

IDENTIFICATION OF WAVE DEFORMATION PROCESSES OF LANDSLIDES IN THE NORTHWESTERN BLACK SEA USING THE INSTRUMENTAL OBSERVATION DATA

Problem Statement and Purpose. At present, considering the conditions of slopes equilibrium, only the stresses caused by gravity, hydrodynamic and seismic effects are most often taken into account. As for tectonic stresses, their effect on landslide slopes has hardly been studied. At the same time, landslides and deformations ofslopes in a wide spatio-temporal range (with the frequency from several months to several dozens of years and the levels of massifs tectonic discreteness from first tensof meters to first kilometres) is also recorded in fact. Empirical data indicate that wave mechanism caused by rotational regime of the Earth can be one of the possible mechanisms explaining the high-frequency quasi-cyclic spatio-temporal variability of the rock mass stress-strain state. Purpose of the work has been to identify wave deformation processes in the Earth’s upper crust according to the data of instrumentalobservation of landslide slopes and relatively long line facilities deformation regime. In this work, we also intend to substantiate the thesis that wave exotectogenesis isone of the factors reducing the overall stability of landslide slopes. Data&Methods. The data of instrumental observations of structural components deformation in the underground drainage facilities of the landslide prevention works on Odesa coast that have accumulated during 50 years of operation, as well as the results of geodetic monitoring of landslide slope and the crest of plateau on the right bank of the Malyi Adzhalyk Liman within the territory of the Port Plant (ammonium plant) in 2000–2019 have been used to study the dynamics of deformation wave processes in the Earth’s upper crust. Statistical and cartographic analyses of the data sets mentioned above were carried out according to traditional methods using the Statistica, Matlab and Surfer software packages. Results. It has been found that modern dynamics of landslide slopes is significantly influenced by the periodic change of the stress-strainstate of rocks in space and time. The authors interpret the empirically revealed alternating in space zones of compression and extension, which cause the dynamics of vertical and horizontal reference benchmarks displacements in the inter-annual regime of marks displacement on the right bank of the Malyi Adzhalyk Liman and in the tunnels of Odesa coast as thereflection of wave geodynamics with periodic change of the stress-strainstate of rocks in space and time. Hierarchical layering of the tectonosphere in depth (the presence of layers with different elastic properties), tectonic discreteness and blockiness of rock massifs determine the spatial framework of the dynamically complex structure of the deformation field. Multiple cycles of compression-extensionof rocks lead to decrease in the rocks strength, accumulation of plastic deformations and activation of landslide displacements even on the coastal areas where anti-landslide measures have been implemented. To prepare design models correctly, it is important to take into account both the landslide formation mechanism and the factors that reduce the overall stability of the slope. The latter include the quasiperiodic variability of the rock mass stress-strain state controlled by rotational dynamics via wave mechanism.

Stars on the Verge: Analyses of the Complex Light Variations of the Hyper-luminous Red Supergiant VY Canis Majoris: On the Nature of the Star’s “Great Dimming” Episodes

Abstract VY Canis Majoris (VY CMa) is one of the largest, most luminous red supergiant (RSG) stars in the Galaxy. This huge oxygen-rich RSG may be on the verge of becoming a bright core-collapse Type-II supernova. Over the 20th century, VY CMa has been undergoing episodic large quasi-periodic light variations. It has experienced two “great dimming” episodes during ∼1920–1950 and ∼1985–1995. During these, the star underwent large (1–2.5 mag) quasi-periodic light variations with dominant periods ranging between ∼1415 and 1565 days. In addition to experiencing large quasi-periodic light variations, VY CMa became fainter by 1.0–1.5 mag during the 1920–1950 episode. There is evidence that the star’s brightness decreased from ∼6.5–7.0 to ∼8.0–8.5 mag from 1850 to after 1900. These long-term dimming events may arise from dust formation from previously expelled gas. The light variations and the “dimmings” of VY CMa far surpass the recent “great dimming” of Betelgeuse.

Homogenization of the wave equation with non-uniformly oscillating coefficients

The focus of our work is a dispersive, second-order effective model describing the low-frequency wave motion in heterogeneous (e.g., functionally graded) media endowed with periodic microstructure. For this class of quasi-periodic medium variations, we pursue homogenization of the scalar wave equation in , , within the framework of multiple scales expansion. When either or , this model problem bears direct relevance to the description of (anti-plane) shear waves in elastic solids. By adopting the lengthscale of microscopic medium fluctuations as the perturbation parameter, we synthesize the germane low-frequency behavior via a fourth-order differential equation (with smoothly varying coefficients) governing the mean wave motion in the medium, where the effect of microscopic heterogeneities is upscaled by way of the so-called cell functions. In an effort to demonstrate the relevance of our analysis toward solving boundary value problems (deemed to be the ultimate goal of most homogenization studies), we also develop effective boundary conditions, up to the second order of asymptotic approximation, applicable to one-dimensional (1D) shear wave motion in a macroscopically heterogeneous solid with periodic microstructure. We illustrate the analysis numerically in one dimension by considering (i) low-frequency wave dispersion, (ii) mean-field homogenized description of the shear waves propagating in a finite domain, and (iii) full-field homogenized description thereof. In contrast to (i) where the overall wave dispersion appears to be fairly well described by the leading-order model, the results in (ii) and (iii) demonstrate the critical role that higher-order corrections may have in approximating the actual waveforms in quasi-periodic media.

ОСОБЛИВОСТІ ВАРІАЦІЙ ХАРАКТЕРИСТИК ВЧ-РАДІОХВИЛЬ В ІОНОСФЕРІ ВПРОДОВЖ СОНЯЧНОГО ЗАТЕМНЕННЯ 21 ЧЕРВНЯ 2020 р. НАД КИТАЄМ

Subject and Purpose.The study of the effect that each new Solar eclipse (SE) has on radio wave characteristics is an actual scientific and technical issue. The purpose of the present work is to analyze the variations in Doppler spectra (DS), Doppler shift of frequency (DSF), and in the reflected wave amplitude (RWA) that were observed during the SE of June 21, 2020 over the People’s Republic of China. Methods and Methodology.The observations of HF radio wave characteristics were made using the Harbin Engineering University multi-frequency multipath coherent radio system. The temporal variations in DS, DSF of the main ray and RWA are analyzed further. The variations in the Doppler frequency shift (DSF) were subjected to a systematic spectral analysis that involved joint application of the windowed Fourier transform, adaptive Fourier decomposition, and the Morlet mother-function-based wavelet transformation. Results. The SE was accompanied by DS diffuseness resulting from an increase in the number of rays. The DSF temporal variations were observed to be bi-polar and asymmetrical, with extreme DSF magnitudes varying from –11 to –40 mHz and from 22 to 56 mHz. The duration of processes with negative DSF values varied from 50 to 80 min, and the duration of processes with positive DSF changed from 30 to 80 min. The multi-hop propagation (from two to five hops) took place along all propagation paths, with a 360 to 560-km one-hop range. The 4–5-min period quasi-periodic DSF variations showed 20–50 mHz amplitude, and the 8–18-min period variations exhibited 40–100 mHz amplitude. The relative amplitudes of the 4–5 min period quasi-periodic variations in the electron density were observed to be in the 0.3–6.2% range, and the amplitudes of the 8–18 min period variations were found to be in the 1.1–21.7% range. A decrease in the electron density along different propagation paths was observed to vary from –(12–16)% to –(20–26)%.

Effects of Varying Mass Inflows on Star Formation in Nuclear Rings of Barred Galaxies

Abstract Observations indicate that the star formation rate (SFR) of nuclear rings varies considerably with time and is sometimes asymmetric rather than being uniform across a ring. To understand what controls temporal and spatial distributions of ring star formation, we run semiglobal, hydrodynamic simulations of nuclear rings subject to time-varying and/or asymmetric mass inflow rates. These controlled variations in the inflow lead to variations in the star formation, while the ring orbital period (18 Myr) and radius (600 pc) remain approximately constant. We find that both the mass inflow rate and supernova feedback affect the ring SFR. An oscillating inflow rate with period Δτ in and amplitude 20 causes large-amplitude (a factor of ≳5), quasi-periodic variations of the SFR when Δτ in ≳ 50 Myr. We find that the time-varying interstellar medium (ISM) weight and midplane pressure track each other closely, establishing an instantaneous vertical equilibrium. The measured time-varying depletion time is consistent with the prediction from self-regulation theory provided the time delay between star formation and supernova feedback is taken into account. The supernova feedback is responsible only for small-amplitude (a factor of ∼2) fluctuations of the SFR with a timescale ≲40 Myr. Asymmetry in the inflow rate does not necessarily lead to asymmetric star formation in nuclear rings. Only when the inflow rate from one dust lane is suddenly increased by a large factor do the rings undergo a transient period of lopsided star formation.

ОСОБЛИВОСТІ ГЕНЕРАЦІЇ ВЕЛИКОМАСШТАБНИХ ЗБУРЕНЬ В ІОНОСФЕРІ ПІД ДІЄЮ МОНОІМПУЛЬСНОГО ТА ПЕРІОДИЧНОГО РАДІОВИПРОМІНЮВАННЯ НАГРІВНОГО СТЕНДА

Subject and Purpose. Considerable attention has traditionally been given to the interaction of high-power radio-frequency emissions with the ionosphere. The great many physical effects taking place within the limits of a powerful (heating) facility’s antenna pattern are subjected here to a thorough and detailed analysis. Also, the application of high-power radio emissions provides a convenient means for studying subsystem coupling in the Earth-atmosphere-ionosphere-magnetosphere system, as well as of generation and propagation of disturbances well beyond the antenna pattern of the transmitter. The present paper has been aimed at analyzing the features revealed by the large-scale ionospheric disturbances as these are generated under the impact of either monopulse or periodic radio-frequency emissions from an HF heating facility. Methods and Methodology. In the course of the experiments, the ionosphere was affected with high power radio frequency emission from the heating facility Sura. The disturbances were diagnosed at a distance of 960 km from the heater, with the aid of a vertical incidence Doppler radar. Results. It has been found that through the period of minimal solar activity the ionospheric disturbances observable at a range about 103 km from the heater did arise as the effective radiated power of the latter approached to 25 MW. The duration of the ionospheric response to the impact of an incident monopulse was equal to the length of that latter, while the quasi-periodic variations shown by the Doppler frequency shift just started to appear. The apparent horizontal speed of the propagating disturbances was found to vary from about 300 m/s to 420 m/s. Note that speed to increase at higher altitudes. The periodic mode of heater operation was accompanied by generation of quasi-periodic disturbances in the electron density, of relative amplitudes about 1% and periods close to the Brunt–Väisälä period. Conclusions. The basic features of Doppler spectrum variations, contained in the signals from a diagnostic radar, have been identified in connection with high-power HF radiation incident on the ionosphere

ЕФЕКТИ СОНЯЧНОГО ЗАТЕМНЕННЯ 10 ЧЕРВНЯ 2021 р. В ІОНОСФЕРІ ВИСОКИХ ШИРОТ: РЕЗУЛЬТАТИ GPS-СПОСТЕРЕЖЕНЬ

Subject and Purpose. The unique natural phenomena which solar eclipses are can activate coupling between the subsystems of the Earth–atmosphere–ionosphere–magnetosphere system. Following an eclipse, disturbances may get induced in all the subsystems and their associated geophysical fields. It is important that a subsystem’s response does not depend on the phase of the eclipse alone, but also on the state of space weather and the observation site coordinates. The majority of solar eclipses occur at middle and low latitudes. The maximum phase of the June 10, 2021 annular eclipse was observed at high latitudes, including the North Pole. The highlatitude ionosphere is fundamentally different from the mid- and low-latitude ionosphere as it stays in a metastable state, such that any impact may be capable of activating subsystem coupling. The relevance of this study is conditioned by the diversity of the solar eclipse effects in the high-latitude ionosphere. The purpose of this work is to present observational results concerning variations in the total electron content (TEC) in the high-latitude ionosphere in the course of the June 10, 2021 solar eclipse. Methods and Methodology. An array of eleven terrestrial GPS receive stations and eight GPS satellites were used for the observations. Results. The effects from the solar eclipse were distinctly observable at all eleven reception sites and from all the eight satellites. On the average, i.e. with random fluctuations neglected, changes in illumination at ionospheric heights were followed by decreases in the TEC. All of the observation records demonstrated a decrease in the TEC at the early stage of the eclipse. Some 60 to 100 min later the TEC attained a minimum and then returned to virtually the initial value. The lowest observed magnitude of the TEC was 1.0–5.1 TEC units, while, on the average, it was found to be 2.7 ± 1.6 TEC units, or 35 ± 18%. The greatest decrease in the TEC lagged behind the maximum phase of the solar eclipse (lowest illumination at the heights of the ionosphere) by 5–30 min, or 15.7 ± 6.8 min on the average. A few TEC records obtained at different stations showed quasi-periodic variations with the periods ranging from 5 to 19 min and amplitudes of 1 to 12%. Conclusions. The annular eclipse of June 10, 2021 acted to significantly disturb the high-latitude ionosphere where aperiodic and quasi-periodic disturbances of the TEC took place.

THE PANDEMIC WAVES’ IMPACT ON ROMANIAN E-MARKET: A NON-LINEAR REGRESSION MODEL

The SARS-COV2 pandemic had a strong impact on the Romanian and European e-Market, manifested by the explosive increase in online sales, especially at the beginning of the two waves of epidemic, in spring and autumn. Using a statistical regressive analysis of monthly change in the volume of online sales in Romania, we propose a non-linear regression model of growth of this commercial sector that take into account the economic and socials effects of the three pandemic waves in 2020-2021, combining logistic equations of growth with attenuated quasi-periodical variations of market. The model allows a prediction of the overall behavior of online buyers for 2021 and 2022, similar to last year, but with annual growth peaks slightly less pronounced than in 2020.

Global MHD Simulation of the Weak Southward IMF Condition for Different Time Resolutions

We performed high-resolution three-dimensional global MHD simulations to determine the impact of weak southward interplanetary magnetic field (IMF) (Bz = −2 nT) and slow solar wind to the Earth’s magnetosphere and ionosphere. We considered two cases of differing, uniform time resolution with the same grid spacing simulation to find any possible differences in the simulation results. The simulation results show that dayside magnetic reconnection and tail reconnection continuously occur even during the weak and steady southward IMF conditions. A plasmoid is generated on closed plasma sheet field lines. Vortices are formed in the inner side of the magnetopause due to the viscous-like interaction, which is strengthened by dayside magnetic reconnection. We estimated the dayside magnetic reconnection which occurred in relation to the electric field at the magnetopause and confirmed that the enhanced electric field is caused by the reconnection and the twisted structure of the electric field is due to the vortex. The simulation results of the magnetic field and the plasma properties show quasi-periodic variations with a period of 9–11 min between the appearances of vortices. Also the peak values of the cross-polar cap potential are both approximately 50 kV, the occurrence time of dayside reconnections are the same, and the polar cap potential patterns are the same in both cases. Thus, there are no significant differences in outcome between the two cases.

Analysis of High-precision TESS Photometry of the Black Hole X-Ray Binary Cygnus X-1: Evidence of Intrinsic Variability of the Luminous Blue Supergiant Component

Abstract We report on Transiting Exoplanet Survey Satellite (TESS) high-precision photometry of the iconic non-eclipsing 5.60 days (O9.7Iab+black hole) binary Cygnus X-1. Previous ground-based photometry reveals low-amplitude (∼0.04 mag) ellipsoidal light-variations that arise from the tidal (and rotational) distortion of the O9.7Iab companion. Additional small light-variations have also been reported by many observers. Short-cadence TESS photometry was conducted over ∼27 days during 2019 July–August. The photometry shows the expected ∼5.60 days binary ellipsoidal variations, but in addition ∼0.01–0.03 mag complex quasi-periodic brightness variations. The observations were analyzed to investigate the underlying extra-binary variability. We also determined a new time of minimum light and calculated an updated period and light elements. The quasi-periodic, (non-binary) light-variations likely arise from the complex pulsations of the blue supergiant.

Unusual Emission Variations Near the Eclipse of Black Widow Pulsar PSR J1720−0533

Abstract We report on an unusually bright observation of PSR J1720−0533 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is in a black widow system that was discovered by the Commensal Radio Astronomy FAST Survey (CRAFTS). By coincidence, a bright scintillation maximum was simultaneous with the eclipse in our observation, which allowed for precise measurements of flux density variations, as well as dispersion measure (DM) and polarization. We found that there are quasi-periodic pulse emission variations with a modulation period of ∼22 s during the ingress of the eclipse, which could be caused by plasma lensing. No such periodic modulation was found during the egress of the eclipse. The linear polarization of the pulsar disappears before the eclipse, even before there is a visually obvious change in DM. We also found that the pulse scattering may play an important role in the eclipse of PSR J1720−0533.

Long-term multi-wavelength variations of Fermi blazar 3C 279

Long-term optical, X-ray and γ-ray data of blazar 3C 279 have been compiled from Swift-XRT, RXTE-PCA, Fermi-LAT, SMARTS and literature. The source exhibits strong variability on long timescales. From the 1980s until now, the optical R band light curve spans more than 32 yr, and a possible 5.6-yr-long quasi-periodic variation component has been found in it. The optical spectral behavior has been investigated. In the optical band, the mean spectral index is –1.71. The source exhibits an obvious special spectral behavior. In the low state, the source manifests a clear bluer-when-brighter behavior in the sense that the optical spectrum turns harder (flatter) when the brightness increases. While in the high state, the optical spectrum is stable, which means the source spectral index does not vary with brightness. The correlation analysis has been performed among optical, X-ray and γ-ray energy bands. The result indicates that the variations of γ-ray and X-ray bands are well correlated without time delay on the timescale of days, and their variations exhibit weak correlations with those of the optical band. The variations, especially outbursts, are simultaneous, but the magnitude of variations is disproportionate. The detailed analysis reveals that the main outbursts exhibit strong correlations in different γ-ray, X-ray and optical bands.