Narrow Results

In this paper one- and two-photon pair production in a subcritical magnetic field have been considered. Two-photon production has been studied in the resonant case, when the cross-section considerably increases compared to the non-resonant case. While one-photon pair production is considered to be the main mechanism of plasma generation in a pulsar magnetosphere, we suggest the existence of another one, which is resonant two-photon production process.

The main features of charged particles accessing the Earth magnetosphere have been studied by tracing their trajectories. The reconstruction code has allowed us to perform two simulations of Cosmic Rays (CRs) accessing the AMS detector, one for the 1998 data, and the other for the 2005 (at the moment, the IGRF data are available up to that year). The parameters of the external field model for 2005 have been estimated from the solar conditions in 1982 and 1984, two solar cycles before. The CRs have been assumed to be isotropically impinging on the AMS detector, flying at 400 km altitude with energies reproducing the AMS-01 observed spectrum. The computation of allowed and forbidden primary particle trajectories has enabled us the estimate of the Transmission Function in both periods. A comparison with the overall (primary and secondary) AMS-01 data provides by subtraction the determination of the secondary spectrum.

The motion of antiprotons in the Magnetosphere region is computed with some initial conditions and the spatial distributions of them are plotted. The antiprotons in the polar region are looked like coming from the outer region. Meanwhile, the antiprotons on the ISS altitude are trapped in the radiation belt. This is explained by the model that antiprotons are originated in decay particles from the antineutrons produced with the cosmic ray interactions in the atmosphere. This also shows that they are rich in the SAA region in the ISS altitudes. In order to distinguish antiprotons from protons effectively, the differences of arrival directions of them are important.

The environs of supermassive black holes are among the universe's most extreme phenomena. Understanding the physical processes occurring in the vicinity of black holes may provide the key to answer a number of fundamental astrophysical questions including the detectability of strong gravity effects, the formation and propagation of relativistic jets, the origin of the highest energy gamma-rays and cosmic rays, and the nature and evolution of the central engine in active galactic nuclei (AGN). As a step towards this direction, this paper reviews some of the progress achieved in the field based on observations in the very high energy domain. It particularly focuses on nonthermal particle acceleration and emission processes that may occur in the rotating magnetospheres originating from accreting, supermassive black hole systems. Topics covered include direct electric field acceleration in the black hole's magnetosphere, ultra-high energy cosmic ray production, Blandford–Znajek mechanism, centrifugal acceleration and magnetic reconnection, along with the relevant efficiency constraints imposed by interactions with matter, radiation and fields. By way of application, a detailed discussion of well-known sources (Sgr A*; Cen A; M87; NGC1399) is presented.

We study the force-free electrodynamics on rotating black holes in the Born–Infeld (BI) effective theory. The stream equation describing a steady and axisymmetric magnetosphere is derived. From its near-horizon behavior, we obtain the modified Znajek regularity condition, with which we find that the horizon resistivity in the BI theory is generally not a constant. As expected, the outer boundary condition far away from the hole remains unchanged. In terms of the conditions at both boundaries, we derive the perturbative solution of split monopole in the slow rotation limit. It is interesting to realize that the correction to the solution relies not only on the parameter in the BI theory, but also on the radius (or the mass) of the hole. We also show that the quantum effects can undermine the energy extraction process of the magnetosphere in the nonlinear theory and the extraction rate gets the maximum in the Maxwell theory.

There is growing evidence for high-frequency gravitational waves (HFGWs) ranging from MHz to GHz. Several HFGW detectors have been operating for over a decade, and two GHz events have been reported recently. However, a confirmed detection might take a decade. This essay argues that unexplained observed astrophysical phenomena, like Fast Radio Bursts (FRBs), might provide indirect evidence for HFGWs. In particular, using the Gertsenshtein–Zel’dovich effect, we show that our model can explain three key features of FRBs: generate peak-flux up to $1000\mathrm{\text{Jy}}$, naturally explain the pulse width and the coherent nature of FRBs. In short, our model offers a novel perspective on the indirection detection of HFGWs beyond current detection capabilities. Thus, transient events like FRBs are a rich source for multi-messenger astronomy.

This paper presents a computational technique for modeling the Earth's magnetic field using the framework of Adaptive Non-Additive Fuzzy System (ANAFS). The defuzzified output constructed from both the premise and consequent parts of the GFM rules takes the form of Choquet integral. Premise and consequent parameters of non-additive fuzzy model are then updated for each online data based on the estimation error to make the adaptive system. The resulting model is applied on the real data, i.e. H-component of the magnetic field obtained from the magnetometer and the training and prediction results are found to be better and can be used for modeling such a complex system whose mathematical or physical modeling is very difficult to obtain. Thus, this work makes an important contribution to the field of fuzzy modeling of real life complex systems.

The analytical expression for Goldreich-Julian (GJ) charge density at the polar cap of magnetized neutron star has been obtained in braneworlds for inclined neutron star through solving Maxwell equations and shown that the value of GJ charge density decreases with increasing the value of the brane charge. The analytical expressions for scalar potential and parallel electric field on the region greater than the polar cap region of the neutron star have also been obtained by solving Poisson equation in braneworlds.

The Marcel Grossmann triennial meetings are focused on reviewing developments in gravitation and general relativity, aimed at understanding and testing Einstein’s theory of gravitation. The 15^th meeting (Rome, 2018) celebrated the 50^th anniversary of the first neutron star discovery (1967), and the birth of relativistic astrophysics. Another discovery of the same caliber is the detection of the binary neutron star GW170817 in 2017 — almost as if to celebrate the same jubilee — marking the beginning of multi-messenger gravitational wave astronomy. We present work in progress to craft open-sourced numerical tools that will enable the calculation of electromagnetic counterparts to gravita- tional waveforms: the GiRaFFE (General Relativistic Force-Free Electrodynamics) code. GiRaFFE numerically solves the general relativistic magnetohydrodynamics system of equations in the force-free limit, to model the magnetospheres surrounding compact binaries, in order (1) to characterize the nonlinear interaction between the source and its surrounding magnetosphere, and (2) to evaluate the electromagnetic counterparts of gravitational waves, including the production of collimated jets. We apply this code to various configurations of spinning black holes immersed in an external magnetic field, in order both to test our implementation and to explore the effects of (1) strong gravitational field, (2) high spins, and (3) tilt between the magnetic field lines and black hole spin, all on the amplification and collimation of Poynting jets. We will extend our work to collisions of black holes immersed in external magnetic field, which are prime candidates for coincident detection in both gravitational and electromagnetic spectra.

Combined influence of rotation of a black hole and ambient magnetic fields creates conditions for powerful astrophysical processes of accretion and outflow of matter which are observed in many systems across the range of masses; from stellar-mass black holes in binary systems to supermassive black holes in active galactic nuclei. We study a simplified model of outflow of electrically charged particles from the inner region of an accretion disk around a spinning (Kerr) black hole immersed in a large-scale magnetic field. In particular, we consider a non-axisymmetric magnetosphere where the field is misaligned with the rotation axis. In this contribution we extend our previous analysis of acceleration of jet-like trajectories of particles escaping from bound circular orbits around a black hole. While we have previously assumed the initial setup of prograde (co-rotating) orbits, here we relax this assumption and we also consider retrograde (counter-rotating) motion. We show that the effect of counter-rotation may considerably increase the probability of escape from the system, and it allows more efficient acceleration of escaping particles to slightly higher energies compared to the co-rotating disk.

Changes in solar activity lead to adverse conditions within the upper atmosphere which may cause disruption of satellite operations, communications, navigation, and electric power grid. The term space weather is used to refer to changes in the Earth's space environment. This paper reviews plasma waves, found in all parts of the ionosphere and magnetosphere, in the context of space weather. Generated by energetic particles within the magnetosphere, these waves in turn cause particle accelerations, heating, and precipitation, taking an active part in determining space weather. Terrestrial lightning is an important source of plasma waves and forms a link between the lower and the upper atmosphere. Though many aspects of plasma waves such as their morphology and association with energetic particles and geomagnetic phenomena are well established, their generation mechanisms in most cases remain elusive. Current research involving active and passive, ground and space borne experiments, modeling, and simulation is providing better understanding of plasma wave generation mechanisms and the relation of plasma waves to other space weather parameters such as variations in geomagnetic field and energetic particle fluxes resulting from solar storms. Potentially, plasma waves could serve as one of the key indicators of space weather.

Dynamics of charged matter in the oblique black hole magnetosphere is investigated. In particular, we adopt a model consisting of a rotating black hole embedded in the external large-scale magnetic field that is inclined arbitrarily with respect to the rotation axis. Breaking the axial symmetry appears to have profound consequences regarding the dynamics of particles and it also poses some methodological difficulties. In this contribution we discuss the applicability of the method of effective potential for the non-axisymmetric model and show that it may only be applied in the appropriate reference frame.

During solar events (such as flares or CME), energetic protons are accelerated in interplanetary medium. These particles are called briefly SEP (solar energetic particles). We estimated the SEP contribution to solar wind pressure. We used data collected by ACE and GOES, in particular during 4 periods, each one of 15 days. Each period is centered on a significant solar flare. We investigated possible effects on terrestrial geomagnetic field.

The structure of radio emission beam is a long standing open question. In this chapter, we briefly reviewed the methods of reconstructing the radio emission beam and the progress on the study of emission beam models. The observational tests for the beam models, especially the test from the precessional pulsar PSR J1906+0746 and its implications are also discussed.