Fast Radio Bursts (FRBs) are millisecond-long bursts of radio emission of extragalactic origin. The nature or FRBs is still unknown. Whether all FRBs are representatives of the same source population, or whether multiple underlying populations exist, is also unknown. One class that stands out is that of the “repeaters”, i.e. FRBs from which multiple bursts have been detected. In these cases, appropriate models should be non-cataclysmic but yet being able to create powerful coherent radio emission. Magnetars are among those source types that are considered as possible explanation for (repeating) FRBs. This review will summarise the basic properties of FRBs and those of magnetars to provide a critical assessment of the possible physical connection between these classes of sources. We conclude that while magnetars may indeed be related to the FRB phenomenon, it is unlikely that they explain all FRBs, i.e. at least two classes of FRBs exist.

Based on our current high resolution direct N-body modelling of the Milky Way typical Star Cluster systems dynamical evolution we try to numerically estimate the influence of individual spin values and orientations on gravitational wave (GW) waveforms and observed time-frequency maps during multiple cycles for binary black hole (BBH) mergers. In our up to date N-body dynamical simulations we use the high order relativistic post-Newtonian corrections for the BH binary particles (3.5 post-Newtonian (PN) terms including spin-spin and spin-orbit terms). In the current work, we present the GW waveforms catalogue which covers the large parameter space in mass ratios 0.05 - 0.82 and extreme possible individual spin cases.

The magnetar SGR J1830–0645 was discovered in outburst in October 2020. We studied its X-ray properties during the first month of the outburst using XMM–Newton, NuSTAR and Swift observations. The shape and amplitude of the pulse profile varied significantly with energy. The broadband spectrum was well described using two absorbed blackbody components plus a faint power law component at high energies. Phase-resolved spectral analysis of the data suggests that the emission could be attributed to thermal photons from a single heated region with a complex shape on the star surface undergoing resonant Compton scattering on charged particles located in the magnetosphere. Modelling the evolutionary path of the magnetar with our magneto-thermal evolutionary codes indicates that SGR J1830 was born ≈23 kyr ago with a dipolar magnetic field of ∼1015 G, slightly larger than the current value.

We continue studying convection as a possible factor of episodic accretion in protoplanetary disks. Within the model of a viscous disk, the accretion history is analyzed at different rates and regions of matter inflow from the envelope onto the disk. It is shown that the burst-like regime occurs in a wide range of parameters. The long-term evolution of the disk is modeled, including the decreasing-with-time matter inflow from the envelope. It is demonstrated that the disk becomes convectively unstable and maintains burst-like accretion onto the star for several million years. The general conclusion of the study is that convection can serve as one of the mechanisms of episodic accretion in protostellar disks, but this conclusion needs to be verified using more consistent hydrodynamic models.

Due to the rich phenomenology and extreme magnetic conditions, magnetars will be targets of great interest for the upcoming polarimetry space missions. In particular, the Imaging X-ray Polarimetry Explorer (IXPE), recently launched in December 2021, will operate in the 2–8 keV range. This will open a new window to study the polarized, persistent X-ray emission from magnetars. In this talk, I will present simulations of IXPE observations of magnetars using the IXPEObsSim package. I will discuss future prospect to discriminate between different magnetar’s emission mechanisms, as well as a potential detection of the signal of vacuum birefringence using IXPE.

Thermal energies deposited by OB stellar clusters in starburst galaxies lead to the formation of galactic superwinds. Multi-wavelength observations of starburst-driven superwinds pointed at complex thermal and ionization structures which cannot adequately be explained by simple adiabatic assumptions. In this study, we perform hydrodynamic simulations of a fluid model coupled to radiative cooling functions, and generate time-dependent non-equilibrium photoionization models to predict physical conditions and ionization structures of superwinds using the maihem atomic and cooling package built on the program flash. Time-dependent ionization states and physical conditions produced by our simulations are used to calculate the emission lines of superwinds for various parameters, which allow us to explore implications of non-equilibrium ionization for starburst regions with potential radiative cooling.

We describe a numerical model of hot Jupiter extended envelope that interacts with stellar wind. Our model is based on approximation of multi-component magnetic hydrodynamic. The processes of ionization, recombination, dissosiation and chemical reactions in hydrogen-helium envelope are taken into account. In particular, the ionization of neutral hydrogen atoms takes place due to processes of photo-ionization, charge-exchange and thermal collisions. Further, this model is supposed to be used for research on biomarkers’ dynamics in extended envelopes of hot Jupiters.

The focus of this work is to comprehensively understand hydro-dynamical back-flows and their role in dynamics and non-thermal spectral signatures particularly during the initial phase of X-shaped radio galaxies. In this regard, we have performed axisymmetric (2D) and three dimensional (3D) simulations of relativistic magneto-hydrodynamic jet propagation from tri-axial galaxies. High-resolution dynamical modelling of axisymmetric jets has demonstrated the effect of magnetic field strengths on lobe and wing formation. Distinct X-shape formation due to back-flow and pressure gradient of ambient is also observed in our 3D dynamical run. Furthermore, the effect of radiative losses and diffusive shock acceleration on the particle spectral evolution is demonstrated, which particularly highlights how crucial their contributions are in the emission signature of these galaxies. This imparts a significant effect on the galaxy’s equipartition condition, indicating that one must be careful in extending its use in estimating other parameters, as the criterion evolves with time.

Pulsating Ultra Luminous X-ray sources (PULXs) are thought to be X-ray bright, accreting, magnetized neutron stars, and could be the first and only evidence for the existence of magnetars in binary systems. Their apparent soft (< 20 keV) X-ray luminosity can exceed the Eddington luminosity for a neutron star (NS) by a few orders of magnitude. Although several scenarios have been proposed to explain the different components observed in the X-ray spectra and the characteristics of the X-ray lightcurve of these system, detailed quantitative calculations are still missing. In particular, the observed soft X-ray lightcurves are almost sinuosidal and show an increase in the pulsed fraction (from 8% up to even 30%) with increasing energy. Here, we present how emission originating from an optically thick envelope, expected to be formed during super-Eddington accretion, can result in pulsed fractions similar to observations.

A detailed description of the properties of dense matter in extreme conditions, as those within Neutron Star cores, is still an open problem, whose solution is hampered by both the lack of empirical data, and by the difficulties in developing a suitable theoretical framework for the microscopic nuclear dynamics in such regimes.

We report here the results of a study aimed at inferring the properties of the repulsive three-nucleon interaction, driving the stiffness of the equation of state at high densities, by performing bayesian inference on current and future astrophysical observations.

The dense matter equation of state (EoS), describing the state of matter under the extreme conditions found in neutron stars, is not accurately known. However, significant process has been made in recent years through the emergence of new observational avenues of neutron stars. Firstly, the X-ray timing telescope NICER has delivered two joint mass-radius measurements, for pulsars PSR J0030+0451 and PSR J0740+6620, using pulse profile modeling. Secondly, gravitational wave detections of binary neutron star (BNS) mergers allow for a measurement of the EoS-dependent tidal deformability, as demonstrated in the first detected BNS merger GW170817. Additionally, electromagnetic radiation from the subsequent ultraviolet-optical-infrared transient (the kilonova) originating from the ejected material in GW170817 further probes the binary system and the EoS. We demonstrate how the joint analysis of these multi-messenger observations of neutron stars significantly constrains the dense matter EoS. We then describe, in more detail, a framework to jointly analyse a gravitational wave signal and the accompanying kilonova light curves, focusing on possible future black hole–neutron star (BHNS) mergers. We highlight the potential for multimessenger BHNS to constrain the tidal deformability of the neutron star, thereby increasing our understanding of the dense matter EoS.

Computational fluid dynamics is a crucial tool to theoretically explore the cosmos. In the last decade, we have seen a substantial methodological diversification with a number of cross-fertilizations between originally different methods. Here we focus on recent developments related to the Smoothed Particle Hydrodynamics (SPH) method. We briefly summarize recent technical improvements in the SPH-approach itself, including smoothing kernels, gradient calculations and dissipation steering. These elements have been implemented in the Newtonian high-accuracy SPH code MAGMA2 and we demonstrate its performance in a number of challenging benchmark tests. Taking it one step further, we have used these new ingredients also in the first particle-based, general-relativistic fluid dynamics code that solves the full set of Einstein equations, SPHINCS_BSSN. We present the basic ideas and equations and demonstrate the code performance at examples of relativistic neutron stars that are evolved self-consistently together with the spacetime.

In the neutron-star mergers, the radioactive decay of freshly synthesized heavy elements produces emissions in the ultraviolet-optical-infrared range, producing a transient called kilonova. The observational properties of the kilonova depend on the bound-bound opacity of the heavy elements, which was largely unavailable for the conditionssuitable at an early time (t < day). In this article, I share some of our recent progress on modeling the early kilonova light curve, focusing on the atomic opacity calculation.

One of the ways to understand the genesis and evolution of the universe is to know how galaxies have formed and evolved. In this regard, the study of star formation history (SFH) plays an important role in the accurate understanding of galaxies. In this paper, we used long-period variable stars (LPVs) for estimating the SFH in the Andromeda galaxy (M31). These cool stars reach their peak luminosity in the final stage of their evolution also their birth mass is directly related to their luminosity. Therefore, using stellar evolution models, we construct the mass function and hence the star formation history.

Situation with highly magnetized neutron stars in binary systems is not yet certain. On the one hand, all best studied magnetars seem to be isolated objects. On the other, there are many claims based on model-dependent analysis of spin properties or/and luminosity of neutron stars in X-ray binaries in favour of large fields. In addition, there are a few results suggesting a magnetar-like activity of neutron stars in close binary systems. Most of theoretical considerations do not favour even existence, not speaking about active decay, of magnetar-scale fields in neutron stars older than ∼106 yrs. However, alternative scenarios of the field evolution exist. I provide a brief review of theoretical and observational results related to the presence of neutron stars with large magnetic field in binaries and discuss perspectives of future studies.

We investigate the broad-band behaviour of circular polarization in radio pulsar profiles and show the relationship between polarization fraction and what proportion of that polarization is circular, both across frequency, and for a large number of pulsars viewed collectively. The behaviour observed may be explained by pulsar polarization originating from the partially-coherent combination of two linearly-polarized orthogonal modes with different flux spectral indices. (See also the poster in the “supplementary information”.)

We numerically investigate the gravitational collapse of rotating magnetic protostellar clouds. The simulations are performed using 2D MHD code ‘Enlil’. The code is based on TVD scheme of increased order of accuracy. We developed a model of the initially non-uniform cloud, which self-consistently treats gas density and large-scale magnetic field distribution. Simulation results for the typical parameters of a solar mass cloud are presented. In agreement with our previous results for the uniform cloud, the isothermal collapse of the non-uniform cloud results in formation of hierarchical structure of the cloud, consisting of flattened envelope and thin quasi-magnetostatic primary disk near its equatorial plane. The non-uniform cloud collapses longer than the uniform one, since the magnetic field is dynamically stronger at the periphery of the cloud in the former case.

The nuclear equation-of-state (EOS) describing newly formed proto-neutron stars (PNSs) in core-collapse supernovae (CCSNe) is yet uncertain, and varying its prescription affects multimessenger signatures in CCSN simulations. Focusing on the gravitational wave (GW) signal, we demonstrate the effect of varying parameter values in the EOS. We conclude that an especially important parameter is the effective mass of nucleons which affect thermal properties and subsequently the PNS compactness, regulating the GW signal in both amplitude and frequency. By radially decomposing the GW emission, we show where in the PNS the GWs originate from.

The population of black widows, binary systems containing a millisecond pulsar and a very low-mass companion star exposed to the high-energy pulsar wind, has grown exponentially in the past few years. The number of black widow candidates is now over 30 systems, but only 14 have been confirmed so far. Their relevance in analysing the extremes of the neutron stars properties led to multiwavelength dedicated studies that revealed a rich phenomenology. In this work, we provide a glimpse into the black widow class through modelling of high-cadence multi-band light curves of 6 systems, accounting for almost half of the confirmed population. A better understanding of the black widow population, which hosts some of the most massive and fastest spinning neutron stars, will ultimately benefit future modelling of compact object mergers.

Many simulations have been performed to elucidate the formation process of first stars. In first star formation, radiative feedback is a key process in determining stellar masses. However, previous simulations which follow the feedback process don’t resolve the small scale ( 10 AU) to realize long-term calculation, and the structure near massive protostars is still unknown. To clarify how the radiation from the protostar works, we need to resolve small scale and calculate the interaction between the radiation and the dense gas in such a region. As a first step towards understanding the phenomenon in this region, we perform the high-resolution simulation around the massive protostar without radiative transfer. We find that dense gas covers the protostar even in the polar direction and the HII region cannot expand. Solving the radiative transfer for getting accurate results is our future work. We are currently developing the new radiation hydrodynamics code for that.