Relation Between Gravitational Mass and Baryonic Mass for Non-Rotating and Rapidly Rotating Neutron Stars

With a selected sample of neutron star (NS) equations of state (EOSs) that are consistent with the current observations and have a range of maximum masses, we investigate the relations between NS gravitational mass Mg and baryonic mass Mb, and the relations between the maximum NS mass supported through uniform rotation (Mmax) and that of nonrotating NSs (MTOV). We find that for an EOS-independent quadratic, universal transformation formula (Mb=Mg+A×M2g)(Mb=Mg+A×Mg2), the best-fit A value is 0.080 for non-rotating NSs, 0.064 for maximally rotating NSs, and 0.073 when NSs with arbitrary rotation are considered. The residual error of the transformation is ∼ 0.1M⊙ for non-spin or maximum-spin, but is as large as ∼ 0.2M⊙ for all spins. For different EOSs, we find that the parameter A for non-rotating NSs is proportional to R−11.4R1.4−1 (where R1.4 is NS radius for 1.4M⊙ in units of km). For a particular EOS, if one adopts the best-fit parameters for different spin periods, the residual error of the transformation is smaller, which is of the order of 0.01M⊙ for the quadratic form and less than 0.01M⊙ for the cubic form ((Mb=Mg+A1×M2g+A2×M3g)(Mb=Mg+A1×Mg2+A2×Mg3)). We also find a very tight and general correlation between the normalized mass gain due to spin Δm = (Mmax − MTOV)/MTOV and the spin period normalized to the Keplerian period PP, i.e., log10Δm=(−2.74±0.05)log10P+log10(0.20±0.01)log10Δm=(−2.74±0.05)log10P+log10(0.20±0.01), which is independent of EOS models. These empirical relations are helpful to study NS-NS mergers with a long-lived NS merger product using multi-messenger data. The application of our results to GW170817 is discussed

Fast Radio Bursts as Strong Waves Interacting with the Ambient Medium

Fast radio bursts (FRBs) are mysterious radio transients whose physical origin is still unknown. Within a few astronomical units near an FRB source, the electric field of the electromagnetic wave is so large that the electron oscillation velocity becomes relativistic, which makes the classical Thomson scattering theory and the linear plasma theory invalid. We discuss FRBs as strong waves interacting with the ambient medium, in terms of both electron motion properties and plasma properties. Several novel features are identified. (1) The cross section of Thomson scattering is significantly enhanced for the scattering photons. (2) On the other hand, because of the nonlinear plasma properties in strong waves, the near-source plasma is more transparent and has a smaller effective dispersion measure (DM) contribution to the observed value. For a repeating FRB source, the brighter bursts would have somewhat smaller DMs contributed by the near-source plasma. (3) The radiation beam undergoes relativistic self-focusing in a dense plasma, the degree of self-focusing (or squeezing) depends on the plasma density. Such a squeezing effect would affect the collimation angle and the true event rate of FRBs. (4) When an FRB propagates in a nearby ambient plasma, a wakefield wave in the plasma will be generated by the ponderomotive force of the FRB, and accelerates electrons in the ambient medium. However, such an effect is too weak to be observationally interesting

Viewing Angle Constraints on S190425z and S190426c and the Joint Gravitational-wave/Gamma-Ray Detection Fractions for Binary Neutron Star Mergers

The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo scientific collaboration (LVC) detected two binary neutron star (BNS) merger candidates, S190425z and S190426c. The Fermi-Gamma-ray Burst Monitor (GBM) observed 55.6% (for S190425z) and 100% (for S190426c) of the probability regions of both events at the respective merger times, but no gamma-ray burst (GRB) was detected in either case. The derived luminosity upper limits suggest that a short GRB similar to GRB 170817A would not be detectable for both cases due to their distances, which are larger than that of GW170817. Assuming that the jet profile obtained from GW170817/GRB 170817A is quasi-universal for all BNS–GRB associations, we derive that the viewing angles of S190425z and S190426c should be... (see abstract in full article)

Testing the Hypothesis of Compact-binary-coalescence Origin of Fast Radio Bursts Using a Multimessenger Approach

In the literature, compact binary coalescences (CBCs) have been proposed as one of the main scenarios to explain the origin of some non-repeating fast radio bursts (FRBs). The large discrepancy between the FRB and CBC event rate densities suggests that their associations, if any, should only apply at most for a small fraction of FRBs. Through a Bayesian estimation method, we show how a statistical analysis of the coincident associations of FRBs with CBC gravitational wave (GW) events may test the hypothesis of these associations. We show that during the operation period of the advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), the detection of ~100 (~1000) GW-less FRBs with dispersion measure (DM) values smaller than 500 pc cm−3 could reach the constraint that less than 10% (or 1%) FRBs are related to binary black hole (BBH) mergers. The same number of FRBs with DM values smaller than 100 pc cm−3 is required to reach the same constraint for binary neutron star (BNS) mergers. With the upgrade of GW detectors, the same constraints for BBH and BNS mergers can be reached with fewer FRBs or looser requirements for the DM values. It is also possible to pose constraints on the fraction of each type of CBCs that are able to produce observable FRBs based on the event density of FRBs and CBCs. This would further constrain the dimensionless charge of black holes (BHs) in binary BH systems

The accuracy of a method for printing three-dimensional spinal models.

To study the morphology of the human spine and new spinal fixation methods, scientists require cadaveric specimens, which are dependent on donation. However, in most countries, the number of people willing to donate their body is low. A 3D printed model could be an alternative method for morphology research, but the accuracy of the morphology of a 3D printed model has not been determined.Forty-five computed tomography (CT) scans of cervical, thoracic and lumbar spines were obtained, and 44 parameters of the cervical spine, 120 parameters of the thoracic spine, and 50 parameters of the lumbar spine were measured. The CT scan data in DICOM format were imported into Mimics software v10.01 for 3D reconstruction, and the data were saved in .STL format and imported to Cura software. After a 3D digital model was formed, it was saved in Gcode format and exported to a 3D printer for printing. After the 3D printed models were obtained, the above-referenced parameters were measured again.Paired t-tests were used to determine the significance, set to P<0.05, of all parameter data from the radiographic images and 3D printed models. Furthermore, 88.6% of all parameters of the cervical spine, 90% of all parameters of the thoracic spine, and 94% of all parameters of the lumbar spine had Intraclass Correlation Coefficient (ICC) values >0.800. The other ICC values were <0.800 and >0.600; none were <0.600.In this study, we provide a protocol for printing accurate 3D spinal models for surgeons and researchers. The resulting 3D printed model is inexpensive and easily obtained for spinal fixation research