CyberSec Research

We introduce a novel method to constrain the Hubble constant ($H_0$) by combining fast radio bursts (FRBs) and their persistent radio sources (PRSs) through the observationally validated Yang relation, $ L_{\nu} \propto | \mathrm{RM} | $, which links PRS luminosity to the rotation measure (RM) of the associated FRB. Using a mock sample of PRSs, we demonstrate that the Yang relation can help to unravel the degeneracies among $H_0$, baryon density parameter $\Omega_b$, and baryon fraction in the intergalactic medium $f_{\mathrm{IGM}}$ in the traditional approach of using dispersion measure only to perform cosmological analyses. Our method employs a two-stage Markov Chain Monte Carlo (MCMC) analysis to constrain $H_0$. Using the available data of six observed PRS systems, we obtain a preliminary constraint of $H_0 = 75 \pm 30~\mathrm{km\,s^{-1}\,Mpc^{-1}}$. We briefly discuss possible refinements of the method by reducing residual degeneracies and systematic uncertainties using future data and physical modeling. Our results indicate that the Yang relation can potentially become a new probe for performing FRB cosmology.

The High Energy Cosmic-Radiation Detection (HERD) facility has been proposed as a leading experiment on China's Space Station (CSS). Scheduled for installation around 2027, HERD is expected to operate for at least a decade. The main scientific objectives include indirect detection of dark matter with unprecedented sensitivity, studying the cosmic-ray spectrum and composition up to the knee, and observing all-sky gamma rays with energies above 100 MeV. HERD is designed as a large-acceptance telescope with a unique design aimed at maximizing its efficiency. It comprises a central 3D imaging calorimeter (CALO) made of LYSO crystals, encircled by four complementary subdetectors on its top and four lateral faces: the scintillating fiber tracking detector (FIT), the plastic scintillator detector (PSD), the silicon charge detector (SCD), and a transition radiation detector (TRD) on one lateral side. To fully harness HERD gamma-ray detection capabilities down to 100 MeV, an advanced ultra-low-energy gamma-ray (ULEG) trigger system has been developed. We present an extensive overview of the design, performance, and optimization of the gamma-ray trigger system supported by software simulations and preliminary results from the successful implementation of the HERD prototype at CERN's PS and SPS beam test campaigns in Fall 2023.

Based on an extended nuclear statistical equilibrium model, we investigate the properties of non-accreted crusts of young and warm neo-neutron stars, i.e., of finite-temperature inhomogeneous dense matter in beta equilibrium. We present two novel results and one known, but frequently ignored property of such matter. The first new feature is the appearance, in the deep inner crust, of an extensive and almost pure $^{14}$He layer that extends up to the density of the transition to homogeneous matter. This layer may challenge the idea of nuclear pasta phases, significantly impact the transport properties and the crust crystallization process. Second, we raise the question of the (in)stability of the inner crust with respect to diffusion of ions (buoyancy) and demonstrate that our crust is stable, in contrast with the predictions of some other models. Finally, we show that subsaturated stellar matter is thermodynamically stable with respect to density fluctuations, which rules out a first-order phase transition between inhomogeneous and homogeneous phases.

We carry out a numerical calculation of magnetar-powered shock break-outs (SBOs) and supernova (SN) light-curves. In particular, we investigate the impact of gravitational wave (GW) emission by the magnetar central engine on its electromagnetic (EM) counterparts in the ULTRASAT band. Our results show that GW emission by the magnetar has only a minor effect on the SBO light-curve. However, we find that SN light-curves can carry a direct signature of GW emission, which becomes more evident at late times (> 20-30 days).~Our results demonstrate that future ULTRASAT observations will provide crucial insights into the magnetar formation process, and unique information for direct searches of long-transient signals with current and future generation GW detectors. In particular, we estimate a rate of multi-messenger (UV+GW) detections of newly formed magnetars $>$ 1 every two years with ULTRASAT and the Einstein Telescope.

Quasi-periodic eruptions (QPEs), the repeated outbursts observed in soft X-ray bands, have attracted broad interest, but their physical origin is under debate. One of the popular models, the star-disk collision model, suggests that QPEs can be produced through periodic collisions of an orbiting star with the accretion disk of a central black hole (BH). However, previous tests of the star-disk collision model mainly focus on the timing analysis. Other observed properties, such as peak luminosities $L_{\rm{p}}$, durations $t_{\rm{e}}$, and radiation temperatures $T_{\rm{p}}$ of the eruptions, are not systematically investigated. For a sample of six QPE sources and two QPE-like sources, we test the star-disk collision model by using these observables to derive the constraints on the stellar radius $R_*$. We find that, except for two sources (eRo-QPE3 and eRo-QPE4), the rest of the sample either has no allowed $R_*$ to simultaneously reproduce the observed $L_{\rm{p}}$ and $t_{\rm{e}}$, or the required $R_*$ is too large to avoid being disrupted by the central BH. For the two exceptions, a stellar radius of the order of $1\ R_{\rm{\odot}}$ is necessary to satisfy all the constraints. Another issue with the simplest version of this model is that it predicts $k T_{\rm{p}} \sim 10\ \rm{eV}$, one order of magnitude lower than the observed value.

We report on the mass measurement of the rapid proton-capture process key nuclide ${}^{84}$Mo and its vicinity, such as ${}^{78}$Y${}^{\rm m}$, ${}^{79}$Y, ${}^{83}$Nb, and ${}^{88}$Ru, using the multi-reflection time-of-flight spectrograph at RIKEN RIBF. For ${}^{78}$Y${}^{\rm m}$, ${}^{84}$Mo, and ${}^{88}$Ru, their masses are experimentally determined for the first time with uncertainties of $\delta m \approx 20~{\rm keV}$. The mass precision of ${}^{79}$Y and ${}^{83}$Nb is improved to 13 keV and 9.6 keV, respectively. The new $\alpha$-separation energy of ${}^{84}$Mo, 1.434(83) MeV, unambiguously rules out the possibility of forming the ZrNb cycle. The X-ray burst simulation with the new masses shows that our measurements effectively remove the large final abundance uncertainties in the $A=80-90$ mass region. The new mass values improve the prediction power for the composition of the nuclear ashes in X-ray bursts, including the production of light $p$-nuclei.

Gravitational-wave (GW) observations of compact binaries have the potential to unlock several remarkable applications in astrophysics, cosmology, and nuclear physics through accurate measurements of the source luminosity distance and inclination. However, these parameters are strongly correlated when performing parameter estimation, which may hamper the enormous potential of GW astronomy. We comprehensively explore this problem by performing Bayesian inference on synthetic data for a network of current and planned second-generation GW detectors, and for the third-generation interferometer Einstein Telescope~(ET). We quantify the role of the network alignment factor, detector sensitivity, and waveform higher-order modes in breaking this degeneracy. We discuss the crucial role of the binary mass ratio: in particular, we find that ET can efficiently remove the error in the distance as long as the compact binary is asymmetric in mass.

Newtonian and post-Newtonian (PN) calculations suggest that each spherical harmonic mode of the gravitational waveforms (radiation) emitted by eccentric binaries can be further decomposed into several eccentricity-induced modes (indexed by $j=1$ to $j=\infty$), referred to as eccentric harmonics. These harmonics exhibit monotonically time-varying amplitudes and instantaneous frequencies, unlike the full eccentric spherical harmonic modes. However, computing or extracting these harmonics are not straightforward in current numerical relativity (NR) simulations and eccentric waveform models. To address this, Patterson \textit{et al} have developed a framework to extract the eccentric harmonics directly from effective-one-body formalism waveforms. In this paper, we build on the ideas presented in Patterson \textit{et al} and propose a data-driven framework, utilizing singular-value decomposition (SVD), that incorporates additional features based on PN intuition to ensure monotonicity in the extracted harmonics. We further demonstrate that the phase (frequency) of these harmonics is simply $j\phi_{\lambda}+\phi_{\rm ecc}$ ($jf_{\lambda}+f_{\rm ecc}$) where $\phi_{\lambda}$ ($f_{\lambda}$) is related to the secular orbital phase (frequency) and $\phi_{\rm ecc}$ ($f_{\rm ecc}$) is an additional phase (frequency) that only depends on the eccentricity. We also provide simple analytical fits to obtain the harmonics as a function of the mean anomaly. These relations may prove useful in constructing faithful models that can be employed in cheap and efficient searches and parameter estimation of eccentric mergers. Our framework is modular and can be extended for any other eccentric waveform models or simulation frameworks. The framework is available through the \texttt{gwMiner} package.

Supernova 2023ixf is a type IIP supernova that was observed in May 2023 in the spiral galaxy Messier 101. This was the closest supernova observed of the decade, making this an exciting discovery. Combining the observed brightness and duration with theoretical scaling relations, we model the lightcurve of this supernova in order to reveal the properties of the progenitor star at the time of explosion, including its mass, radius, and explosion energy. We simulate these explosions using the stellar evolution and radiation-hydrodynamics codes MESA+STELLA. We find that SN2023ixf is not easily explained with "normal" stellar evolution, and only models with a small mass of H-rich ejecta can fit the lightcurve. We also find that the late time properties of the lightcurve are better fit by a higher initial-mass star with substantial mass loss during its lifetime, as compared to models with lower initial mass and less mass loss.

We present gwharmone, the first data-driven surrogate model for eccentric harmonics (as well as the full radiation content) of the dominant quadrupolar mode in eccentric, non-spinning binary black hole mergers. Our model is trained on 173 waveforms, each $100,000M$ long (where $M$ is the total mass), generated for mass ratios $q \in [1,3.5]$ and eccentricities $e_{\rm ref} \in [0,0.2]$ (at the start of the waveform). The eccentric harmonics are extracted from the effective-one-body waveforms using the \texttt{gwMiner} package. We apply a singular value decomposition (SVD) to obtain a set of reduced basis vectors, necessary to construct a lower-dimensional representation of data, and use Gaussian Process Regression (GPR) to interpolate SVD coefficients across parameter space, allowing for prediction at new parameter points. The model includes the effect of mean anomaly, its evaluation cost is only $\sim 0.1$ second and it achieves an average time-domain (validation) error of ~0.001 and frequency-domain (validation) mismatches below 0.01 for advanced LIGO sensitivity. Our model can therefore be useful in efficient searches and parameter estimation of eccentric mergers. gwharmone will be publicly available through the gwModels package.

We present the first contemporaneous X-ray and optical polarimetric measurement of the extremely high synchrotron peaked (EHSP) blazar H 1426+428. The X-ray polarimetric observations were undertaken using the Imaging X-ray Polarimetry Explorer (\textit{IXPE}) on 2024 May 27, and 2024 July 5. The \textit{IXPE} pointings were accompanied by contemporaneous optical observations of the Observatorio de Sierra Nevada, Calar Alto Observatory and the Perkins Telescope Observatory. While we observed the X-ray degree of polarization to be $>20\%$, the polarization in the optical band was found to be only $1-3\%$. This trend has been observed in several HSP blazars with available optical and X-ray polarimetric data and is typically explained in terms of energy stratification downstream of a shock. However, we observed a significant difference between the optical and X-ray polarization angles, a feature that has been observed in certain HSP blazars, such as Mrk 421, but remains a relatively rare or underreported phenomenon. We discuss possible scenarios for these findings within the framework of a partially turbulent jet model.

We present near-infrared follow-up observations of the International Gravitational Wave Network (IGWN) event S250206dm with the Wide-Field Infrared Transient Explorer (WINTER). WINTER is a near-infrared time-domain survey designed for electromagnetic follow-up of gravitational-wave sources localized to $\leq$300 deg$^{2}$. The instrument's wide field of view (1.2 deg$^2$), dedicated 1-m robotic telescope, and near-infrared coverage (0.9-1.7 microns) are optimized for searching for kilonovae, which are expected to exhibit a relatively long-lived near-infrared component. S250206dm is the only neutron star merger in the fourth observing run (to date) localized to $\leq$300 deg$^{2}$ with a False Alarm Rate below one per year. It has a $55\%$ probability of being a neutron star-black hole (NSBH) merger and a $37\%$ probability of being a binary neutron star (BNS) merger, with a $50\%$ credible region spanning 38 deg$^2$, an estimated distance of 373 Mpc, and an overall false alarm rate of approximately one in 25 years. WINTER covered $43\%$ of the probability area at least once and $35\%$ at least three times. Through automated and human candidate vetting, all transient candidates found in WINTER coverage were rejected as kilonova candidates. Unsurprisingly, given the large estimated distance of 373 Mpc, the WINTER upper limits do not constrain kilonova models. This study highlights the promise of systematic infrared searches and the need for future wider and deeper infrared surveys.

We perform simulations of magnetohydrodynamic accretion onto equal-mass, non-spinning binary black holes in 3+1 full general relativity addressing the effects of orbital eccentricity. We find that binary black holes with non-negligible eccentricity accrete matter with periodicity that matches the binary orbital period, whereas quasi-circular binaries exhibit accretion rate modulation at approximately $\sim 0.7\times$ their binary orbital period. Additionally, we find that the total jet luminosity is modulated at the orbital period for eccentric binaries, while quasi-circular binaries only exhibit long-term modulations. We perform a radiative transfer calculation of the dual jet synchrotron emission and demonstrate that the optically thin synchrotron emission varies on the binary orbital period for eccentric binaries. Moreover, eccentric binaries spend more time in a low state, where the synchrotron emission is minimum, than in a high state, where the synchrotron emission peaks. The quasi-circular binary also exhibits variability in its optically thin synchrotron emission but the exact frequency of variability does not appear robust against different parameters. Our suite of simulations is an essential step towards providing a comprehensive catalog of multi-messenger theoretical models that will enable studies of supermassive binary black holes detectable across the electromagnetic and gravitational wave spectra.

We present the most sensitive search to date for light axion-like particles with masses below a micro-eV, using spectropolarimetric data collected from the Lick and Keck Observatories. The conversion of optical photons emitted from the surface of a magnetic white dwarf (MWD) into axions in the strong magnetic field around the star induces a nearly wavelength-independent linear polarization in the observed starlight. We analyze the Stokes parameters $(U, Q, I)$ measured with the Kast spectrograph at the Lick Observatory toward the MWDs SDSS J033320+000720 and ZTF J190132+145807, and with the LRISp-ADC instrument at the Keck Observatory toward ZTF J190132+145807, SDSS J002129+150223, and SDSS J100356+053825 to search for this effect. The data show no evidence of axion-induced linear polarization, and we set world-leading constraints on the axion-photon coupling $|g_{a\gamma\gamma}| \lesssim 1.7 \times 10^{-12} \,\mathrm{GeV}^{-1}$ at the $95\%$ confidence level for masses $m_a \lesssim 2 \times 10^{-7}\,\mathrm{eV}$.

GW170817 is the first binary neutron star merger detected with gravitational and electromagnetic waves, and its afterglow is still detectable 7 years post-merger. Some previous studies of the X-ray afterglow have claimed the onset of a new afterglow component or raised concerns about the data processing techniques. Motivated thus, we present here a reanalysis of X-ray afterglow data for GW170817 and find potential sources of discrepancies between the data reduction techniques employed by various research groups. We also analyze the updated panchromatic afterglow data to find that there is no significant evidence for any new afterglow component (e.g. due to the ejecta that gave rise to the kilonova) and that the jet must be still in a mildly relativistic phase. The decline in the afterglow light curve is significantly shallower compared to that expected from the standard synchrotron afterglow jet models with sideways spreading, indicating either an additional energy injection at late times or the velocity dependence on the microphysics parameters. In this context, we discuss the implications of the late time afterglow data on jet dynamics.

We investigate the impact of chemical equilibration and the resulting bulk viscosity on non-radial oscillation modes of warm neutron stars at temperatures up to T~5 MeV, relevant for protoneutron stars and neutron-star post-merger remnants. In this regime, the relaxation rate of weak interactions becomes comparable to the characteristic frequencies of composition g-modes in the core, resulting in resonant damping. To capture this effect, we introduce the dynamic sound speed, a complex, frequency-dependent generalization of the adiabatic sound speed that encodes both the restoring force and the dissipative effects of bulk compression. Using realistic weak reaction rates and three representative equations of state, we compute the complex frequencies of composition g-modes with finite-temperature profiles. We find that bulk viscous damping becomes increasingly significant with temperature and can completely suppress composition g-modes. In contrast, the f-mode remains largely unaffected by bulk viscosity due to its nearly divergence-free character. Our results highlight the sensitivity of g-mode behavior to thermal structure, weak reaction rates, and the equation of state, and establish the dynamic sound speed as a valuable descriptor characterizing oscillation properties in dissipative neutron star matter.

Observations of several gamma-ray bursts (GRBs) that are temporally and spatially compatible with energetic supernovae (hypernovae) has established their common origin. In one case (GRB 111209A/SN 2011kl) the associated supernova was classified as superluminous (SN 2011kl). The exceptional duration of the observed gamma-ray prompt emission of GRB 111209A (about 7 hours) is widely considered key to unlocking the physics behind the still mysterious origin of superluminous supernovae (SLSNe). We review the main observational and theoretical findings that may link some ultra-long GRBs to SLSNe. Specifically, we examine notable events, the role of progenitors and host galaxies in shaping these phenomena, and focus on the proposed models. While a magnetar central engine is a plausible mechanism for both luminous and long-duration GRBs, a conclusive answer remains elusive, as alternative explanations are still viable. Further observational and theoretical work is required to clarify progenitor pathways and explosion mechanisms, potentially extending the classical GRB-SN connection to rare superluminous hypernovae.

Recent three-dimensional magnetohydrodynamical simulations of the common-envelope interaction revealed the self-consistent formation of bipolar magnetically driven outflows launched from a toroidal structure resembling a circumbinary disk. So far, the dynamical impact of bipolar outflows on the common-envelope phase remains uncertain and we aim to quantify its importance. We illustrate the impact on common-envelope evolution by comparing two simulations -- one with magnetic fields and one without -- using the three-dimensional moving-mesh hydrodynamics code AREPO. We focus on the specific case of a $10 M_\odot$ red supergiant star with a $5 M_\odot$ black hole companion. By the end of the magnetohydrodynamic simulations (after $\sim 1220$ orbits of the core binary system), about $6.4 \%$ of the envelope mass is ejected via the bipolar outflow, contributing to angular momentum extraction from the disk structure and core binary. The resulting enhanced torques reduce the final orbital separation by about $24 \%$ compared to the hydrodynamical scenario, while the overall envelope ejection remains dominated by recombination-driven equatorial winds. We analyze field amplification and outflow launching mechanisms, confirming consistency with earlier studies: magnetic fields are amplified by shear flows, and outflows are launched by a magneto-centrifugal process, supported by local shocks and magnetic pressure gradients. These outflows originate from $\sim 1.1$ times the orbital separation. We conclude that the magnetically driven outflows and their role in the dynamical interaction are a universal aspect, and we further propose an adaptation of the $\alpha_\mathrm{CE}$-formalism by adjusting the final orbital energy with a factor of $1+ M_\mathrm{out}/\mu$, where $M_\mathrm{out}$ is the mass ejected through the outflows and $\mu$ the reduced mass of the core binary. (abridged)