Astronomische Nachrichten最新文献

UTC(k) can be considered a shorthand for the local time standard maintained by a country's or region's time- frequency laboratory. Each lab uses its local atomic clocks to maintain this standard and synchronizes it with Coordinated Universal Time (UTC). Although local atomic clocks can operate independently, they generally rely on UTC as a reference standard for precision and long-term stability. To effectively monitor local atomic clocks and improve monitoring efficiency, this paper aims to study new monitoring methods from the perspective of macroscopic astrometry. By utilizing the measurement results of millisecond pulsars and combining them with clock models, this paper focuses on calculating and predicting the deviation data of local atomic clocks. This method not only expands the means of monitoring local atomic clocks but also has significant implications for improving monitoring accuracy and reliability. To validate its effectiveness, we first calculate and analyze the actual and simulated data of millisecond pulsars, then compare the analysis results with the conventional clock deviation data of local clocks based on UTC as a reference. The results indicate that using millisecond pulsars for monitoring can feasibly obtain the phase and frequency deviations of local atomic clocks within a 95% confidence interval. This demonstrates the feasibility of this method. Therefore, monitoring local atomic clocks using millisecond pulsars is reliable and effective. This study provides new insights and methods for the monitoring of local clocks and is significant for improving monitoring accuracy and reliability.

We investigate the behavior of cold quark matter under strong magnetic fields in the frame of a nonlocal NJL model in the chiral limit. Our analysis focuses on deconfinement, chiral symmetry restoration, and the anisotropy in pressure induced by the external magnetic field. For $��\mathrm{eB}�\lesssim �0.07��{\mathrm{GeV}}^2�$, the critical chemical potential remains largely insensitive to the magnetic field, whereas at higher field strengths, transitions to chirally restored phases occur at progressively lower chemical potentials. The parallel and perpendicular pressures, with respect to the magnetic field, exhibit distinct behaviors, reflecting the anisotropic nature of the system. Oscillations in the quark number density, driven by the de Haas–van Alphen effect, reflect the quantized behavior of quarks in a magnetic field. Similarly, the magnetization displays oscillatory behavior, driven by the sequential filling of Landau levels (LLs). At lower external magnetic field strengths, contributions from orbital angular momentum and the population of higher LLs further modulate these oscillations. These results provide deeper insights into the thermodynamic and magnetic properties of quark matter under strong magnetic fields, with implications for astrophysical studies.

The majority of nearby low-luminosity active galactic nuclei (LLAGNs), are widely found in compact radio cores and/or weak jets. The central of galaxy is believed to be powered by hot accretion flow and jet. Besides the famous LLAGN sources M87 and Sgr A*, NGC 315 is also a well-known supermassive black hole (SMBH), which can be used to explore accretion and jet physics. The aim of this work is to model the multi-wavelength spectral energy distribution (SED) of the NGC 315, and all the data we used here in the literature correspond to the core emission. Similarly to M87 and Sgr A*, we find that the SED is hard to fit with a pure jet model or pure advection-dominated accretion flow (ADAF). And with a coupled ADAF-jet model, we find that the low-frequency radio emission is better fitted by the synchrotron radiation of nonthermal electrons in the jet, and high-frequency radio emission is mainly consistent with the inverse Compton radiation from electrons in ADAF. Furthermore, the high-energy X-ray emission can also be simultaneously explained by ADAF. From the SED fitting, we obtain important parameters of the central engine, we find that the SMBH in NGC 315 should be fast rotating with a dimensionless spin parameter $��a_{*}�\simeq �0.9�$, and only a small fraction of the material captured at the outer radius reaches the SMBH. These results will help us better understand the accretion and jet physics. And future further simultaneous multi-wavelength observations will help us to better understand these questions.

The population of compact objects both Galactic and extragalactic can now be studied and verified observationally with increasing efficiency, the latter thanks to the detection of compact object mergers through gravitational waves. The formation channels of merging compact object binaries are, however, not yet fully understood, and may even vary over cosmic time. We address this problem with a population synthesis approach, including BOSSA, a new initial sampling code, to deal with the variation of initial conditions and evaluate its consequences.

Outflows are ubiquitous in various astrophysical objects, yet the mechanism responsible for generating outflows remains unclear. One possibility is that outflows are driven by large-scale magnetic fields. When dealing with magnetically driven outflows, the one-dimensional model proposed by Weber and Davis in 1967 is often employed. However, as it was originally a non-relativistic theory, this limits its application in high-energy astrophysical scenarios. This work attempts to modify the non-relativistic Bernoulli equation into its relativistic form through an analogy method, thereby applying it to relativistic outflows and comparing the results with those of classical theory. We find that when the initial temperature of the outflow is sufficiently high or when the angular velocity of rotation of the magnetic field lines is sufficiently fast, the terminal velocity of the outflow can be relativistic. The relativistically modified Bernoulli equation established in this paper could be conveniently applied in the context of extremely high-velocity outflows from different sources.

We review a general relativistic (GR) method to determine the black hole (BH) parameters: Mass-to-distance ratio, position, and recessional velocity of active galactic nuclei (AGNs) of Seyfert type, which have an accretion disk with water masers circulating around the BH. This GR method makes use of astrophysical observations: The redshifted and the blueshifted photons emitted from the aforementioned masers and their orbital position on the sky. In order to perform the estimations we implement a Bayesian statistical method to fit the above mentioned observational data. One of the main results of this work consists in analytically expressing the gravitational redshift, allowing us to quantify its magnitude for the photons emitted by the closest masers to the black holes. We present this quantity for several BHs hosted at the core of AGNs.