We study flux and spectral variability of the high energy peaked TeV blazar PG 1553 + 113 on diverse timescales using the data collected from 2005 to 2019 which also includes the intensive ...intra-night monitoring of the target. Additionally, we recorded the brightest flare of the blazar PG 1553 + 113 during April 2019 when the source attained an
R
-band magnitude of 13.2. Analyzing the spectral evolution of the source during the flare gave a clockwise spectral hysteresis loop and a time lag with
V
-band variations leading to the
R
-band ones. Various statistical tests, fitting procedures and cross-correlation techniques are applied to search for periodicity and examine the color-magnitude relationship. We find a median period of (2.21 ± 0.04) years along with the secondary period of about 210 days. Finally, we briefly discuss various physical mechanisms which are capable of explaining our findings.
We developed a method that allows to classify the light curves of eclipsing binaries of the W UMa type (EW) with respect to their intrinsic variability. The algorithm measures several features of ...light curves, such as the amplitude of the O’Connell effect, the separation and location of maxima brightness as well as depths of the minima in subsequent orbital periods. This method is capable of distinguishing systems with presumed magnetic activity present from these without it, as well as recognizing systems with starspots migration and those with other types of intrinsic variability manifestation. The classification is done in an automatic way without a time consuming, visual inspection of light curves.
The occurrence of low-amplitude flux variations in blazars on hourly timescales, commonly known as microvariability, is still a widely debated subject in high-energy astrophysics. Several competing ...scenarios have been proposed to explain such occurrences, including various jet plasma instabilities leading to the formation of shocks, magnetic reconnection sites, and turbulence. In this Letter, we present the results of our detailed investigation of a prominent, five-hour-long optical microflare detected during the recent WEBT campaign on 2014 March 2-6 targeting the blazar 0716+714. After separating the flaring component from the underlying base emission continuum of the blazar, we find that the microflare is highly polarized, with the polarization degree ~(40-60)% + or - (2-10)% and the electric vector position angle ~(10-20)degrees + or - (1-8)degrees slightly misaligned with respect to the position angle of the radio jet. The microflare evolution in the (Q,U) Stokes parameter space exhibits a looping behavior with a counterclockwise rotation, meaning the polarization degree decreases with the flux (but is higher in the flux decaying phase), and an approximately stable polarization angle. The overall very high polarization degree of the flare, its symmetric flux rise and decay profiles, and also its structured evolution in the Q-U plane all imply that the observed flux variation corresponds to a single emission region characterized by a highly ordered magnetic field. As discussed in the paper, a small-scale but strong shock propagating within the outflow, and compressing a disordered magnetic field component, provides a natural, though not unique, interpretation of our findings.
By using 78 newly determined timings of light minima together with those collected from the literature, we analysed the changes in the observed minus calculated (O−C) diagram in HS 0705+6700, a ...short-period (2.3 h) eclipsing binary that consists of a very hot subdwarf B-type (sdB) star and a very cool fully convective red dwarf. We confirmed the cyclic variation in the O−C and refined the parameters of the circumbinary brown dwarf (reported to orbit the binary system in 2009) by analysing the changes for the light travel time effect that arises from the gravitational influence of the third body. Our results indicate the lower mass limit of the third body to be M
3 sin i
′ = 33.7(±1.6) M
Jup. This companion would be a brown dwarf if its orbital inclination is larger than 27
7 and it is orbiting the central eclipsing binary with an eccentricity e ∼ 0.2 at a separation of about 3.7(±0.1) au.
We present results from analysis of combined spectroscopic and photometric data for three eclipsing binary systems: AP And, VZ Cep and V881 Per. Based on new, multicolour photometric light curves and ...spectroscopically determined mass ratio values, we derived accurate physical parameters of the components. Two of the systems, namely VZ Cep and V881 Per, were found to be magnetically active. The variability of V881 Per was studied in several sets of data Northern Sky Variability Survey (NSVS), Wide Angle Search for Planets (WASP) and newly derived gathered at different epochs. We show that the huge differences in the shape of its light curve can be explained by just a single model differing only in number of spots and their location on the surface of the primary component.
Machine learning algorithms have been available since the 1990s, but it is much more recently that they have come into use also in the physical sciences. While these algorithms have already proven to ...be useful in uncovering new properties of materials and in simplifying experimental protocols, their usage in liquid crystals research is still limited. This is surprising because optical imaging techniques are often applied in this line of research, and it is precisely with images that machine learning algorithms have achieved major breakthroughs in recent years. Here we use convolutional neural networks to probe several properties of liquid crystals directly from their optical images and without using manual feature engineering. By optimizing simple architectures, we find that convolutional neural networks can predict physical properties of liquid crystals with exceptional accuracy. We show that these deep neural networks identify liquid crystal phases and predict the order parameter of simulated nematic liquid crystals almost perfectly. We also show that convolutional neural networks identify the pitch length of simulated samples of cholesteric liquid crystals and the sample temperature of an experimental liquid crystal with very high precision.
This article reviews recent studies of memory systems in humans and nonhuman primates. Three major conclusions from recent work are that (i) the capacity for nondeclarative (nonconscious) learning ...can now be studied in a broad array of tasks that assess classification learning, perceptumotor skill learning, artificial grammar learning, and prototype abstraction; (ii) cortical areas adjacent to the hippocampal formation, including entorhinal, perirhinal, and parahippocampal cortices, are an essential part of the medial temporal lobe memory system that supports declarative (conscious) memory; and (iii) in humans, bilateral damage limited to the hippocampal formation is nevertheless sufficient to produce severe anterograde amnesia and temporally graded retrograde amnesia covering as much as 25 years.
HS 0705+6700 is a short-period (P = 2.3 hr), close binary containing a hot sdB-type primary and a fully convective secondary. We have monitored this eclipsing binary for more than two years and as a ...result, 32 times of light minimum were obtained. Based on our new eclipse times together with these compiled from the literature, it is discovered that the observed-calculated curve of HS 0705+6700 shows a cyclic variation with a period of 7.15 years and a semiamplitude of 92.4 s. The periodic change was analyzed for the light-travel time effect that may be due to the presence of a tertiary companion. The mass of the third body is determined to be M 3sin i' = 0.0377(±0.0043) M when a total mass of 0.617 M for HS 0705+6700 is adopted. For orbital inclinations i' >= 328, the mass of the tertiary component would be below the stable hydrogen-burning limit of M 3 ~ 0.072 M , and thus it would be a brown dwarf. The third body is orbiting the sdB-type binary at a distance shorter than 3.6 AU. HS 0705+6700 was formed through the evolution of a common envelope after the primary becomes a red giant. The detection of a substellar companion in HS 0705+6700 system at this distance from the binary could give some constraints on stellar evolution in such systems and the interactions between red giants and their companions.
We announce the discovery of a unique combination of features in a radio source identified with the merger galaxy CGCG 292−057. The radio galaxy both exhibits a highly complex, X-like structure and ...shows signs of recurrent activity in the form of double-double morphology. The outer lobes of CGCG 292−057 are characterized by low radio power, P
1400 MHz≃ 2 × 1024 W Hz−1, placing this source below the FR II/FR I luminosity threshold, and are highly polarized (almost 20 per cent at 1400 MHz) as is typical of X-shaped radio sources. The host is a low-ionization nuclear emission-line region-type galaxy with a relatively low black hole mass and double-peaked narrow emission lines. These features make this galaxy a primary target for studies of merger-triggered radio activity.
Photometric solutions of two short period close binaries, V473 Cas and II Per, are derived with the 2003 version Wilson-Van Hamme code. It is shown that V473 Cas is a semidetached system with the ...primary component or the secondary component at its critical Roche Lobe, while II Per is a marginal contact binary system with both components filling their critical Roche Lobes, but with a large temperature difference between the two components. Both systems belong to near-contact binaries with the light curves enhanced around the left shoulder of secondary minimum, which can be explained by hot spots on the secondary components due to the mass transfer via a stream hitting the facing surface of the secondary components. The orbital period investigations based on all available times of light minimum show a secular period existing in these two targets decreasing at the rate of dP/dt = -7.61 X 10-8 days yr-1 for V473 Cas and dP/dt = -7.54 X 10-8 days yr-1 for II Per. The decrease of the orbital period can be the result of mass transfer from the primary component to the secondary one, which is consistent with the asymmetric light curves of V473 Cas and II Per. Therefore, V473 Cas and II Per are other examples displaying evidence of mass transfer between the two components. We have collected NCBs with secular period variation and find that almost all SD1-type NCBs show decreasing periods and enhancing luminosity on the left shoulder of secondary minimum in their light curves. So the semidetached configuration with the lobe filling primary is more plausible for V473 Cas. Furthermore, the detected enhancing amplitude of luminosity for SD2-type NCBs is smaller than other types of NCBs, which implies that the mass transfer from the primary component to the secondary one is stronger than the transfer in opposite direction. With the orbital period decrease, V473 Cas and II Per will evolve into overcontact binaries with true thermal contact.
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