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Pulsars identified in the LOFAR Two-metre Sky Survey at 144 MHz
No full textWe present the astrometric identification of 80 known radio pulsars as unresolved continuum sources detected at 144 MHz in the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2), which covers 27% of the northern hemisphere. These identifications represent the majority (≥86%) of radio pulsars present in the LoTSS DR2 footprint and provide independent celestial positions and flux densities at 144 MHz. We compare LoTSS flux densities with literature values from various image- and time-domain observations and find good agreement for all but two pulsars. We attribute these flux density deviations to intrinsic pulsar properties (nulling and off-pulse emission). We investigate criteria to select promising pulsar candidates using data from the upcoming LoTSS release of the entire northern sky (δ > 0°), as well as the LOFAR LBA Sky Survey (LoLSS) at 54 MHz (covering δ > 24°). Of the 80 detections, 35 (44%) were blindly redetected based on their linear or circular polarization. Therefore, we conclude that candidate selection based on polarization properties is a promising approach. Candidate selection can be supplemented with spectral indices via cross-matching to LoLSS sources at 54 MHz, as the high sensitivity of LoTSS is not matched by image-domain surveys at higher frequencies
Delving into the depths of NGC 3783 with XRISM
No full textUsing XRISM/Resolve 439 ks time-averaged spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 3783, we investigated the nature of the Fe Kα emission line at 6.4 keV, the strongest and most common X-ray line observed in AGNs. Even the narrow component of the line is resolved with evident Fe Kα1 (6.404 keV) and Kα2 (6.391 keV) contributions with a 2:1 flux ratio, fully consistent with a neutral gas with negligible bulk velocity. The narrow and intermediate-width components have a full width at half maximum of 350 ± 50 km/s and 3510 ± 470 km/s, respectively, suggesting that they arise in the outer disk/torus and/or broad line region. We detect a 10% excess flux around 4–7 keV that is not described well by a symmetric Gaussian line but is consistent with a relativistically broadened emission line. In this study we took the simplest approach, modelling the asymmetric line as a single emission line (assuming neutral, He-like, or H-like iron) convolved with a relativistic disk line model. As expected, the inferred inclination angle (i) is highly sensitive to the assumed ionisation state and ranges between 17 and 44°. This model also constrains the black hole spin via the extent of the red wing: the required gravitational redshift in the fitted disk-line profile disfavours a non-spinning (Schwarzschild) black hole. The derived inner radius is close to the radius of the innermost stable circular orbit (rISCO) and is strongly correlated with the black hole spin. To better constrain the spin, we fixed the inner radius to rISCO and derived a lower limit on the spin of a ≥ 0.29 at the 3σ confidence level. A Compton shoulder is detected in our data as well as a 2–3σ detection of the Cr Kα and Ni Kα lines
An efficient spectral Poisson solver for the
No full textContext. The stability of a differentially-rotating fluid subject to its own gravity is a problem with applications across wide areas of astrophysics, from protoplanetary discs to entire galaxies. The shearing box formalism offers a conceptually simple framework for studying differential rotation in the local approximation.
Aims. Aimed at self-gravitating, and importantly, vertically stratified protoplanetary discs, we develop two novel methods for solving Poisson’s equation in the framework of the shearing box with vertical vacuum boundary conditions (BCs).
Methods. Both approaches naturally make use of multi-dimensional fast Fourier transforms (FFTs) for computational efficiency. While the first one exploits the linearity properties of the Poisson equation, the second, which is slightly more accurate, consists of finding the adequate discrete Green’s function (in Fourier space) adapted to the problem at hand. To this end, we have derived, in Fourier space, an analytical Green’s function satisfying the shear-periodic BCs in the plane as well as vacuum BCs, vertically.
Results. Our spectral method demonstrates excellent accuracy, even with a modest number of grid points, and exhibits third-order convergence. It has been implemented in the NIRVANA-II
Dust destruction by the supernova remnant forward shock in a turbulent interstellar medium
No full textContext. While supernova remnants (SNRs) have been observed to produce up to 1 M⊙ of dust, the amount of dust destroyed by the forward shock is poorly constrained, raising the question of whether they are net dust producers or destroyers.
Aims. Our aim was to estimate the dust destruction efficiency of SNR forward shocks in a realistically turbulent interstellar medium (ISM) during their most destructive phase, and to assess dust shielding by high-density filaments during this period.
Methods. We ran 3D high-resolution turbulence simulations for different turbulent Mach numbers (0–3) and average ISM densities (1–100 cm−3) to resemble observations of the turbulent ISM. We then set off a supernova explosion to trace its 3D magnetohydrodynamic evolution for the first 10 kyr. Finally, we ran post-processing simulations to investigate the dust transport and destruction by the SNR forward shock, taking into account gas and plasma drag, kinetic and thermal sputtering, and grain–grain collisions, and considering either silicates or carbonaceous dust.
Results. The dust destruction rate of the forward shock strongly depends on the average ISM density and turbulence strength, varying in the range 27–92% (0.85–11.0 M⊙) in the studied 10 kyr. Overall, dust is less efficiently destroyed in a low-density medium (1 cm−3, 27–57%) than in intermediate-density (10 cm−3, 46–92%) and high-density (100 cm−3, 73–87%) cases. The forward shock is found to destroy 8–34% less dust in high Mach turbulence compared to a homogeneous medium. Furthermore, carbonaceous grains are up to 21% more robust than silicates.
Conclusions. Filaments can partly shield dust from destruction in the first 10 kyr; however, always more than 0.85 M⊙ of dust is destroyed, making most SNRs dust sinks under the conditions explored in this work. The destruction efficiency of the SNRs with less than 1 M⊙ of destroyed dust has not yet plateaued, so that they are most likely also net dust destroyers by the end of their lifetimes
Star-forming galaxies in the cosmic web in the last 11 Gyr
No full textWe investigate how the star formation activity of galaxies depends on their position within the cosmic web using the SIMB
Exploring the connection between compact object mergers and fast X-ray transients
No full textContext. The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesised but never ultimately established.
Aims. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP 250207b, whose precise positions lie close to nearby (z ≲ 0.1) quiescent galaxies with a negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe.
Methods. We used Chandra to derive accurate localisations for both events and secure otherwise ambiguous associations with their optical counterparts. Deep optical and near-infrared observations with VLT, GTC, and LBT were performed to characterise the surrounding environment and search for kilonova emission, the hallmark of neutron star mergers. Complementary early-time X-ray monitoring with Swift and Einstein Probe was used to constrain the non-thermal afterglow.
Results. We find that both FXRTs remain compatible with a compact binary merger progenitor, which produced low-mass ejecta and kilonova emission subdominant to the afterglow. However, alternative explanations such as a distant (z ≳ 1) core-collapse supernova cannot be conclusively ruled out
Validity test of
No full textThe 16O+16O fusion reaction is important for understanding explosive oxygen burning during late evolutionary stages of massive stars as well as for understanding low-energy heavy-ion fusion-reaction mechanism. This paper represents the first step to determine the excitation function for the major exit channels, Si and P, toward stellar energies indirectly by the Trojan Horse Method via the 16O(20Ne,Si)4He and 16O(20Ne,P)4He three-body reactions. Indeed, here we report on a validity test of the approach showing, for the first time, the possibility to use 20Ne as Trojan Horse nucleus. Results on the reaction channel identification and reaction mechanism determination, with particular emphasis on the momentum distribution of the O inter-cluster motion in the projectile 20Ne nucleus are thoroughly discussed. Fair agreements of the present results with theoretical predictions indicate a possibility to identify the quasi-free process, which is the first step for the application of the Trojan Horse method to independently measure the 16O+16O fusion cross section in the next future
Threshold resummation for
No full textWe present results for threshold resummation of the invariant mass distribution, for on-shell production of a pair of W bosons at next-to-next-to-leading order + next-to-next-to-leading logarithmic(NNLO+NNLL) accuracy in QCD. Owing to its sensitivity to the self-interactions between gauge bosons, this process is important to investigate at the energies of the Large Hadron Collider(LHC). We achieve this resummation by exploiting the factorization properties of the soft and virtual parts of the partonic cross-section. Our analysis has been carried out for the invariant mass distribution up to Q = 2500 GeV. At this highest Q we find that, for 13.6 TeV LHC, the NNLL resummation enhances the NNLO cross-sections by about and reduces the conventional scale uncertainties from at NNLO to at NNLO+NNLL. We also estimate the intrinsic uncertainties due to the non-perturbative parton distribution functions at the highest perturbative order, for both fixed-order and resummed results, to be around for 2000 GeV
Parameter constraints on Horndeski rotating black hole through quasiperiodic oscillations
No full textIn this paper, we perform small perturbations around the circular timelike orbit in the equatorial plane of the Horndeski rotating black hole, and analyze the effects of Horndeski hair on the three fundamental frequencies of the epicyclic oscillations. Since this operation can model the quasiperiodic oscillations (QPOs) phenomena of the surrounding accretion disc, we then employ the MCMC simulation to fit the theoretical results with three QPO events, including GRO J1655-40, XTE J1859+226 and H1743-322, and constrain the characteristic radius r, black hole mass M and spinning parameter a, and the Horndeski hair parameter h. Our constraint on the Horndeski hair parameter is much tighter than QPOs simulation from the existed accretion models, suggesting slight deviation from classical Kerr black hole
The spatial distribution of dwarf and giant galaxies in and around the Virgo cluster
No full textThe Virgo cluster is one of the closest clusters to us where we can further study the evolution of galaxies, with several infalling substructures and several filaments around it that have been reported. Therefore, it makes this cluster and its surrounding area an interesting place to study the spatial distribution of the population of dwarf and bright giant galaxies. We analysed the dwarf fraction (DF) in different regions of the cluster, inside the virial radius, in its surrounding area, and in the filamentary structure surrounding it using available catalogues with the aim of measuring whether the DF changes in different environments. Although the total dwarf fraction within the cluster is ∼0.8, significant local variations are measured throughout the cluster; there are regions with a relatively higher concentration of giant or dwarf galaxies. The fact that Virgo is embedded in a rich environment surrounded by several filaments that feed the cluster with new substructures could imply changes in the DF locally. When we analysed the DF variation at further distances from the cluster we observe some regions with few or no giant galaxies at all, with a local DF ranging from 0.8−1.0. Additionally, when comparing the dwarf fraction in different environments, overall the DF is larger in regions further away from denser regions such as the Virgo cluster and its filamentary structure surrounding it. When comparing the filament and the cluster area, the DF is slightly higher in the filaments, but from filament to filament, the DF changes depending on the presence of groups