Astronomische Nachrichten最新文献

Low-frequency spectral studies of radio pulsars represent a key method for uncovering their emission mechanisms, magnetospheric structure, and signal interactions with the surrounding interstellar medium (ISM). In recent years, more next-generation low-frequency radio telescopes (e.g., LOFAR, LWA and MWA) have enriched the observational window below 350 MHz, enabling more detailed explorations of the ISM effects, such as absorption and scattering, resulting in diverse spectral behaviors observed across different pulsars. This paper reviews the morphology of pulsar radio spectra, advances in spectral modeling, and the key physical processes governing the low-frequency emission. Looking ahead, next-generation instruments such as SKA-Low—with their unprecedented sensitivity—are expected to resolve outstanding questions in pulsar emission processes, offering insights into the extreme physical regimes governing these exotic objects.

Neutron stars are natural laboratories of cold, dense strong interacting matter. In this article, we briefly review the gravitational waves related to neutron stars. Tidal deformability is a significant value that relates the observation of gravitational waves to the equation of state of cold, dense matter. The implicants of GW170817 and GW190814 are discussed. We also give an outlook for future work.

Active galactic nuclei (AGN) especially of blazar type are among the most luminous objects that have been detected through the whole range of the electromagnetic spectrum. It is generally believed that the powered by the central black hole AGN jets are responsible for the observed features like highly variable non-thermal emission characterized by spectral energy distribution extending from radio frequencies up to very high energy gamma-rays. The investigations of the physical properties of jets as well as the mechanisms of jet launching and localization of emissions in AGN are carried out with multi-wavelength observations of active galaxies at the different activity states to trace the temporal changes of fluxes and spectral behavior. NGC 1275 is one of the nearest and extensively studied active galaxies at the energy range from radio band to very high energy gamma-rays. Its multi-wavelength long-term observations resulted in the broadband spectral energy distribution of NGC 1275 obtained simultaneously or quasi-simultaneously and revealed the short-term and long-term timescale variability of emission fluxes from this AGN. Modeling of the NGC 1275 spectral energy distribution at the different activity states was made to estimate the jet physical parameters which may help to understand the changes in the temporal and spectral behavior of NGC 1275 active galactic nucleus.

Active galactic nucleus (AGN) phenomenon and role of jets, powered by the central black hole of AGN, in the feedback of the surroundings on different scales is a matter of detailed multi-wavelength investigations. The long-term observations of AGN are used to reveal the processes taking place in the very proximity to the super-massive black holes. One of the approaches to such studies is to detect the launching of jet components viewed in the radio range and then link it with flaring events detected at higher energy ranges. Tracking the jet-initiated variability events through multiwavelength observations as well as their cross-identification from radio frequencies up to high-energy gamma-rays allows one to locate the regions responsible for the generation of observable features, which can lead to the exploration of the mechanism of jet launching and the origin of emission in the Active Galactic Nucleus. Being nearby and bright, NGC 1275 is one of the extensively studied AGN. This object is very active in the timescales of decades. Multiwavelength long-term observations of NGC 1275 resulted in the detection of different timescale variability from this AGN. For the case of NGC 1275, the cross-correlation of the activity at radio, X-ray, and very high-energy gamma-rays is investigated. The time dependence of the activity of NGC 1275 in the wide energy range was found, which allows one to localize the sites of the emission generation, including one of the very high energies. These multiwavelength long-term studies are highly important for the further advance of the AGN's black hole research and investigations of mechanisms of jet formation.

Blazars are among the most powerful objects in the Universe, whose photon spectrum extends from radio to very high energy gamma-rays (γ-rays). Spectral energy distribution (SED) of blazars has a two-humped shape, whose low-energy part originates from the leptonic mechanism of synchrotron radiation of relativistic electrons in the blazars' jets. It is generally believed that the high-energy part of the spectral energy distribution is of hadronic and leptonic scenarios, but different localization of the source of emission within the core region or far beyond is considered. Also, blazars' emission is characterized by rapid variability at all wavelengths. The tracking of the flaring events at the radio band to connected ones at higher energies may allow localizing emission regions. High-frequency peaked Bl Lacertae type of blazar objects (HBL) are characterized by multi-wavelength variability and SED peaking at the GeV–TeV energy range. Thus, HBL objects have been considered as the best candidate for the sources of very high γ-rays. Mkn 180 is the HBL object with the spectrum that has been measured through radio and X-ray bands to high energy γ-rays. The study of the connection between the outbursts from Mkn 180 viewed from radio to very high energy γ-rays is presented together with its features at the MeV–TeV energy range. These results can help find the parameters for the models of generation of high-energy γ-ray emission in Bl Lac-type objects.

Mkn 180 is the BL Lac object with the spectrum that has been measured through radio and x-ray band to high energy gamma-rays. This object is considered as a potential candidate for the source of high-energy leptonic and/or hadronic cosmic-ray acceleration. Also, it has been proposed to be a GeV–TeV gamma-ray source. The very high energy gamma-rays from Mkn 180 were detected due to the trigger switched on by an optical burst. Mkn 180 was monitored in the optical wave band and in the high and very high energy gamma-rays for a long period and its light curve was obtained. The spectral energy distribution of Mkn 180 blazar was obtained in the wide energy range as well. The spectral energy distributions of blazars consist of two broad peaks. The first, lower frequency peak occurring between radio and soft x-ray energies is due to the synchrotron emissions of relativistic electrons population. Leptonic and hadronic emission mechanisms are considered to describe the second, higher frequency spectrum part between x-ray and VHE gamma-ray energies. The Inverse Compton emissions of the same electrons (synchrotron self-Compton model) or combined with an external Compton mechanism originating from the broad-line region, or the accretion disk are considered in the leptonic scenario. Also, the high energy spectrum part is supposed to be generated due to the processes of photohadronic or hadronuclear interactions of cosmic rays with radiation or matter in the AGN's jet emission region. The multiwavelength observations of Mkn 180 including the GeV–TeV energy data can help to clarify the dominant mechanism of generation of high-energy gamma-ray emission in this object (and whether it can be the source of UHECRs).

Rotational irregularities are one of the prominent observational features that most pulsars exhibit. These glitches, which are sudden increases in spin angular velocity, remains an open problem. In this study, we have investigated the potential role of nontrivial topological defects, specifically in the form of Nambu-Goto type cosmic strings, and its connection to spin irregularities. Such cosmic strings which are one-dimensional topological defects may be formed during various symmetry-breaking and phase transition scenarios and can interact with the neutron stars. In this work, we see that the appearance of such topological defects trapped within the core can lead to the coupling of the string tension with the angular velocity, leading to the abrupt rotational changes observed as pulsar glitches. Further we see, these coupling may generate detectable gravitational waves as a mixture of continuous and burst signals. The evolution of cusps of cosmic strings trapped within neutron stars and the neutron star's mass quadruple moment change due to rotation could produce distinctive gravitational wave signatures, well within the noise cutoff of advLIGO. Our study highlights a potential connection between topological defects, pulsar glitches, and gravitational wave emissions, offering a possible avenue for observationally testing their astrophysical effects.