Study of electric currents excitation in the plasma of the L-2M stellarator with its electronic cyclotronic creation and heating

The results of measuring the longitudinal electric current excited in the toroidal plasma of the L-2M stellarator as a result of powerful pulsed microwave heating (power up to 600 kW, pulse duration up to 20 ms) are presented. In the experi-ments, to create and heat plasma in the stellarator, microwave radiation of gyro-trons with a frequency of 75 GHz, equal to the frequency of the 2nd harmonic of electron cyclotron resonance for a magnetic field with induction B = 1.34 T at the center of the plasma column, was used. To measure the currents in the plasma, di-agnostic systems of the stellarator were used, designed to record changes in time of the transverse and poloidal magnetic fields. It is shown that the presence of an ohmic heating iron transformer in the stellarator design significantly affects the temporal development of equilibrium currents due to the significant inductance of the toroidal plasma. When compensating the inductance of these devices, the ex-pected value of the current excited in the plasma can reach a value of about 7 kA.

Magnetorotational core collapse of possible GRB progenitors – II. Formation of protomagnetars and collapsars

ABSTRACT We assess the variance of the post-collapse evolution remnants of compact, massive, low-metallicity stars, under small changes in the degrees of rotation and magnetic field of selected pre-supernova cores. These stellar models are commonly considered progenitors of long gamma-ray bursts. The fate of the protoneutron star (PNS) formed after the collapse, whose mass may continuously grow due to accretion, critically depends on the poloidal magnetic field strength at bounce. Should the poloidal magnetic field be sufficiently weak, the PNS collapses to a black hole (BH) within a few seconds. Models on this evolutionary track contain promising collapsar engines. Poloidal magnetic fields smooth over large radial scales (e.g. dipolar fields) or slightly augmented with respect to the original pre-supernova core yield long-lasting PNSs. In these models, BH formation is avoided or staved off for a long time, hence, they may produce protomagnetars (PMs). Some of our PM candidates have been run for $\lesssim 10\,$ s after core bounce, but they have not entered the Kelvin–Helmholtz phase yet. Among these models, some display episodic events of spin-down during which we find properties broadly compatible with the theoretical expectations for PMs ($M_\rm {\small PNS}\approx 1.85{-}2.5\, \mathrm{M}_{\odot }$, $\bar{P}_\rm {\small PNS}\approx 1.5 {-} 4\,$ ms, and $b^{\rm surf}_\rm {\small PNS}\lesssim 10^{15}\,$ G) and their very collimated supernova ejecta have nearly reached the stellar surface with (still growing) explosion energies $\gtrsim {2} \times 10^{51}\, \textrm {erg}$.

Axisymmetric equilibrium models for magnetised neutron stars in scalar-tensor theories

Among the possible extensions of general relativity that have been put forward to address some long-standing issues in our understanding of the Universe, scalar-tensor theories have received a lot of attention for their simplicity. Interestingly, some of these predict a potentially observable non-linear phenomenon, known as spontaneous scalarisation, in the presence of highly compact matter distributions, as in the case of neutron stars. Neutron stars are ideal laboratories for investigating the properties of matter under extreme conditions and, in particular, they are known to harbour the strongest magnetic fields in the Universe. Here, for the first time, we present a detailed study of magnetised neutron stars in scalar-tensor theories. First, we showed that the formalism developed for the study of magnetised neutron stars in general relativity, based on the “extended conformally flat condition”, can easily be extended in the presence of a non-minimally coupled scalar field, retaining many of its numerical advantages. We then carried out a study of the parameter space considering the two extreme geometries of purely toroidal and purely poloidal magnetic fields, varying both the strength of the magnetic field and the intensity of scalarisation. We compared our results with magnetised general-relativistic solutions and un-magnetised scalarised solutions, showing how the mutual interplay between magnetic and scalar fields affect the magnetic and the scalarisation properties of neutron stars. In particular, we focus our discussion on magnetic deformability, maximum mass, and range of scalarisation.

Deformation of neutron stars due to poloidal magnetic fields

The mass–radius (MR) relation of deformed neutron stars in the axially symmetric poloidal magnetic field is calculated. The MR relation is obtained by solving the Hartle equations, whereas the one for spherical stars is obtained by the Tolman–Oppenheimer–Volkoff equations. The anisotropic effects of the poloidal magnetic fields are found to be non-negligible for a strong magnetic field more than $3\times10^{18}$ G at the center of a neutron star.

A new perspective on the radio active zone at the Galactic center – feedback from nuclear activities

Based on our deep image of Sgr A using broadband data observed with the VLA† at 6 cm, we present a new perspective of the radio bright zone at the Galactic center. We further show the radio detection of the X-ray Cannonball, a candidate neutron star associated with the Galactic center SNR Sgr A East. The radio image is compared with the Chandra X-ray image to show the detailed structure of the radio counterparts of the bipolar X-ray lobes. The bipolar lobes are likely produced by the winds from the activities within Sgr A West, which could be collimated by the inertia of gas in the CND, or by the momentum driving of Sgr A*; and the poloidal magnetic fields likely play an important role in the collimation. The less-collimated SE lobe, in comparison to the NW one, is perhaps due to the fact that the Sgr A East SN might have locally reconfigured the magnetic field toward negative galactic latitudes. In agreement with the X-ray observations, the time-scale of ∼1 × 104 yr estimated for the outermost radio ring appears to be comparable to the inferred age of the Sgr A East SNR.