The 10 most-cited articles in Astronomische Nachrichten, 2019

Disc instability models predict that for X‐ray binaries in quiescence, there should be a brightening of the optical flux prior to an X‐ray outburst. Tracking the X‐ray variations of X‐ray binaries in quiescence is generally not possible, so optical monitoring provides the best means to measure the mass accretion rate variability between outbursts, and to identify the beginning stages of new outbursts. With our regular Faulkes Telescope/Las Cumbres Observatory (LCO) monitoring we are routinely detecting the optical rise of new X‐ray binary outbursts before they are detected by X‐ray all‐sky monitors. We present examples of detections of an optical rise in X‐ray binaries prior to X‐ray detection. We also present initial optical monitoring of the new black hole transient MAXI J1820+070 (ASASSN‐18ey) with the Faulkes, LCO telescopes, and Al Sadeem Observatory in Abu Dhabi, UAE. Finally, we introduce our new real‐time data analysis pipeline, the “X‐ray Binary New Early Warning System (XB‐NEWS)” which aims to detect and announce new X‐ray binary outbursts within a day of first optical…

The capabilities of telescopes allow the plotting of light curves a routine task. This one shifts the main attention of the astronomer from plotting to research. To achieve this goal, we developed a new tool for the automated reduction of photometric observations, which includes the computational method for the brightness assessment of the investigated and comparison stars, brightness equalization of astronomical images using an inverse median filter, as well as light curve plotting and processing using different tools.

Abstract Symbiotic variable stars belong to an interesting class of interacting binary systems. Since the beginning of this century, the systematic search for these objects has begun, and such surveys have led to discoveries of many new objects and dozens of candidates in the Milky Way and the Local Group. As the latest catalogue of symbiotic binaries is almost two decades old, we decided to prepare a new, online database of the galactic and extragalactic symbiotic systems. These objects are also known for their X‐ray emission. For the purpose of this work, we have prepared a census of symbiotic binaries and their properties based on observations obtained by X‐ray satellites in the previous decades. As our review has shown, the X‐ray emission seems to be a common feature of symbiotic systems, preferentially detected from nearby sources.

Abstract We investigate the application as a technique of the so‐called finite‐time Lyapunov exponent, a scalar value that measures the average, or integrated, separation between trajectories in integrable dynamical systems to quantify the predictability limit of the asymptotic global behavior of old compact star systems (1–10 Gyr), for instance, neutron stars. For this purpose, the Hamiltonian systems with a three‐dimensional self‐gravitating axisymmetric potential are superimposed due to the influence of different birth and kick velocity distributions. We find the behavior of the density distributions P(x) for the finite‐time exponents, which follow a log‐normal distribution (transformed into a Gaussian distribution), with a given mean deviation centered around the global values, at larger Δt. It is shown that simple models of distributions reflect the underlying dynamics. We also analyze the predictability and the deviation vector ω(t), obtained from the distributions, by randomly selecting the initial deviation directions, and consequently the stellar dynamic stability of the…

Abstract The Cosmological Principle is the assumption that the universe is spatially homogeneous and isotropic on the large‐scale average. In 1998, the author, together with his two colleagues, demonstrated that the BATSE's short gamma ray bursts are not distributed isotropically in the sky. This claim was then followed by other papers confirming both the existence of anisotropies in the angular distribution of bursts and the existence of huge Gpc structures in the spatial distribution. These observational facts are in contradiction with the Cosmological Principle because the large‐scale average can hardly be provided. The aim of this study is to survey these publications.

The analysis of blazars' parameters from BZCAT leads to a conclusion that they do not have the same properties. The preliminary criterion to include an object in the catalog was the strong radio emission; however, two type of radio sources were selected: BL Lacertae (BLL) objects and Flat Spectrum Radio Quasars (FSRQ). As a number of properties are typical of blazars (strong radio emission, optical variability, continuum optical spectra, polarization, high luminosity, etc.), using the optical data, we investigate them to clarify which property plays the most significant role in their classification as blazars. We found that 60% of blazars have optical variability. We use a technique developed based on POSS1 and POSS2 photometry and group the variability into extreme, strong, medium, and low classes. In the optical range, 51 blazars have powerful variability (extreme variables), and 126 are high variables. In addition, 63% of blazars have detected radiation in X‐ray and 28% have detected radiation in gamma rays. We give the average statistical characteristics of blazars based on our…

Since 2013, the mass of pulsar PSR J0348 + 0432 (M = 2.01M⊙) has provided a tight constraint on neutron star (NS) equation of state. However, a number of different analyses of the recently detected binary neutron star (BNS) merger (GW170817) point to a maximum NS mass around 2.16M⊙. In addition, a recent study determined the mass of the millisecond pulsar PSR J2215 + 5135 to be . In this work, we investigate the presence of hyperons in NS matter in light of these new mass measurements using equations of state calculated in the relativistic mean‐field approximation. Particular attention is paid to the use of the available empirical data from the study of hypernuclei and that of the SU(3) symmetry relations in fixing the meson‐hyperon coupling constants. We find that hyperonic equations of state with reasonable choices for the meson‐hyperon coupling constants can satisfy these new mass constraints, with hyperons potentially accounting for more than 10% of the baryons in the core of a NS.

The search for the true ground state of dense matter has remained open since Edward Witten proposed the strange matter hypothesis in 1984. In this hypothesis, the strange matter is assumed to be composed of u, d, and s quarks, having an energy per baryon lower than that of quark matter (only u and d), and even lower than that of the nuclear matter. In this sense, neutron stars would be strange stars. Later work showed that a color‐flavor‐locked (CFL) state would be preferred to the one without any pairing for a wide range of the parameters (gap Δ, strange quark mass ms, and bag constant B). We use an approximate, yet very accurate, CFL equation of state (EoS) to obtain exact solutions for the static Einstein field equations that describe a compact relativistic object, providing the first solution directly connected with microphysics.

Abstract The present article is a study of the effect of small perturbations ϵ and ϵ′ in the Coriolis and centrifugal forces, respectively, on the existence and stability of the equilibrium points in the Robe's restricted three‐body problem when the smaller primary is a finite straight segment. The effect of small perturbations in the centrifugal force has a substantial effect on the location of the equilibrium points, but a small perturbation in the Coriolis force has no impact on them. The present model has two collinear, two out‐of‐plane, and an infinite number of noncollinear equilibrium points. Furthermore, we have discussed the stability of the equilibrium points analytically. The collinear equilibrium points L1 and L2 are found to be conditionally stable for the parameters μ, k, l, ϵ, and ϵ′. It is perceived that, for any ϵ with ∣ϵ ∣ ≪ 1 and ϵ′ ≤ 0.2, L1 is stable, and for ϵ′ ≥ 0.23, it becomes unstable. Furthermore, for any ϵ with |ϵ| ≪ 1 and ϵ′ ≤ −0.025, L2 is stable, and for ϵ′ ≥ −0.024, it becomes unstable. The noncollinear and out‐of‐plane equilibrium points are always…

Abstract The predictions of General Relativity suggest a universe in which, as we follow time backward , the hotter and the more dense it was, and the more rapidly it was expanding and that, around 13.7 billion years ago, at the extreme gravitational regime of its evolutionary process, the density, temperature, and expansion rate of the universe would start off as infinite. The General Relativity prediction of a singularity in the early universe would impose a limitation to our understanding of the cosmos and gravity, implying loss of logic and of formal consistency and predictability, making it impossible to impose initial conditions. These extreme conditions of the initial state of the universe are very far from our experimental possibilities, and presently, theoretical models allow only speculations about the avoidance of physical singularities or about the physical conditions that allow circumvent this drastic consequence of General Relativity. Speculations aside, in this study, we follow an analytical line in which we apply the tools of singular semi‐Riemannian geometry to push…