Impulsive acceleration of strongly magnetized relativistic flows

The definitive version can be found at: http://onlinelibrary.wiley.com/ Copyright Royal Astronomical SocietyThe strong variability of magnetic central engines of active galactic nuclei (AGNs) and gamma-ray bursts (GRBs) may result in highly intermittent strongly magnetized relativistic outflows. We find a new magnetic acceleration mechanism for such impulsive flows that can be much more effective than the acceleration of steady-state flows. This impulsive acceleration results in kinetic-energy-dominated flows that are conducive to efficient dissipation at internal magnetohydrodynamic shocks on astrophysically relevant distances from the central source. For a spherical flow, a discrete shell ejected from the source over a time t0 with Lorentz factor Γ∼ 1 and initial magnetization σ0=B20/4πρ0c2≫ 1 quickly reaches a typical Lorentz factor Γ∼σ1/30 and magnetization σ∼σ2/30 at the distance R0≈ct0. At this point, the magnetized shell of width Δ∼R0 in the laboratory frame loses causal contact with the source and continues to accelerate by spreading significantly in its own rest frame. The expansion is driven by the magnetic pressure gradient and leads to relativistic relative velocities between the front and back of the shell. While the expansion is roughly symmetric in the centre of the momentum frame, in the laboratory frame, most of the energy and momentum remains in a region (or shell) of width Δ∼R0 at the head of the flow. This acceleration proceeds as Γ∼ (σ0R/R0)1/3 and σ∼σ2/30 (R/R0)-1/3 until reaching a coasting radius Rc∼R0σ20, where the kinetic energy becomes dominant: Γ∼σ0 and σ∼ 1 at Rc. The shell then starts coasting and spreading (radially), its width growing as Δ∼R0(R/Rc), causing its magnetization to drop as σ∼Rc/R at R > Rc. Given the typical variability time-scales of AGNs and GRBs, the magnetic acceleration in these sources is a combination of the quasi-steady-state collimation acceleration close to the source and the impulsive (conical or locally quasi-spherical) acceleration farther out. The interaction with the external medium, which can significantly affect the dynamics, is briefly addressed in the discussion.Peer reviewe

Gamma ray emission from magnetized relativistic GRB outflows

We argue that small pitch angle synchrotron emission provides an important dissipation mechanism which has to be taken into account in the models of formation of relativistic magnetized gamma-ray burst (GRB) outflows from the newborn black holes and/or magnetars. We show that if the GRB outflow is proton loaded, spectral energy distribution of this emission is expected to sharply peak in 0.1-1~MeV energy band. If the small pitch angle synchrotron emission efficiently cools relativistic particles of the outflow, its spectrum below the peak energy is a powerlaw with spectral index alpha ~ -1, close to the typical spectral index of the time-resolved GRB spectra. Otherwise, the low energy spectral index can be as hard as alpha ~ 0, as observed at the beginning of the GRB pulses. We make a conjecture that small pitch angle synchrotron emission from proton-loaded magnetized GRB outflow could significantly contribute to the Band component of the prompt emission of GRBs while electromagnetic cascade initiated by the protons could be responsible for the GeV component.Comment: 5 pages, 1 figure, accepted for publication in A&A letter

Preliminary results of investigation of solid interplanetary matter in the vicinity of the moon

Density of matter near moon found to be greater than that of interplanetary spac

Hydrorehabilitation children with diseases of the spine by means of swimming

One of the problems of any state maintaining the health of children. For many years one of the leading places in the structure of pathology in children is a disease of the musculoskeletal system. The most common ones are bad posture – they are identified, according to various authors, 65-72% of childrenОдна из актуальных проблем любого государства – сохранение здоровья детей. На протяжении многих лет одно из ведущих мест в структуре патологии детей занимают заболевания опорно-двигательного аппарата. Наиболее частыми из них являются нарушения осанки – они выявляются, по данным различных авторов, у 65-72% дете

Central engines of Gamma Ray Bursts. Magnetic mechanism in the collapsar model

In this study we explore the magnetic mechanism of hypernovae and relativistic jets of long duration gamma ray bursts within the collapsar scenario. This is an extension of our earlier work [1]. We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state and takes into account the cooling associated with emission of neutrinos and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe solutions with different black hole rotation, mass accretion rate, and strength of progenitor's magnetic field. Some of them exhibits strong explosions driven by Poynting-dominated jets with power up to $12\times10^{51} {erg s}^{-1}$. These jets originate from the black hole and powered via the Blandford-Znajek mechanism. A provisional criterion for explosion is derived. A number of simulation movies can be downloaded from http://www.maths.leeds.ac.uk/~serguei/research/movies/anim.htmlComment: 4 pages, 3 figures, GAMMA08 Heidelberg Symposiu

New Social World: The Great Power of the Network

At the early beginning of the 21st century, it was impossible to imagine how fast the Internet would develop. It was also not obvious that the worldwide network would actually become available in all parts of the planet, and the network itself would become the basis for the birth and development of new global products - social networks, communications, and services. According to the International Telecommunication Union, the Internet and new digital products along twenty years have almost completely absorbed the population of developed countries (87%) and are growing rapidly in developing countries (47%)[1]. The affordable cost of communication for the majority of the population together with free communication services create the basis for the emergence of not only new products but also a constant increase in the number of digital services, which quite recently could only be obtained offline. Together with large digital government services, commercial networks, communicators, and services are creating a new social structure capable of independent machine learning and development. The work aims to show that much faster than it was supposed new digital products will intertwine with each other, forming a new social platform, which is called a New Social World. The analysis of sociological works on this topic together with an analysis of practical research on the Internet and new digital products confirms this assumption. Despite strict user agreements, global online monitoring, constant online control and full access to the data of each user, more and more people become users of social networks and services, and most social network users become loyal users of other new products and services, easily switching on digital consumption and consumption of real products and services provided online. The new social reality, generated by the powerful interweaving of the world's digital products and services will forever change the sociocultural and media world. An urgent and constant study of this phenomenon is necessary since the ways of its further development are unpredictable both in relation to the existence of traditional, social, national identification and with the existence of traditional state institutions and states.   Cite this paper: Komissarov, Sergey N.; Vasilyev, Nikolay A. (2021). "New Social World: The Great Power of the Network" Journal of Social Sciences: Transformations & Transitions (JOSSTT) 1(02):08. DOI: https://doi.org/10.52459/josstt1281221

More evidence for extinction of activity in galaxies

This Research Note amends an article in which we showed that radio-loud quasars can become radio-quiet. Exploring the analogy between galactic nuclei and X-ray binaries (XRB), we pointed out there that this transition in quasars could be identified with a switch from low/hard to high/soft state in microquasars. Here, we present the evidence that traces of past occurrences of this kind of phenomena can be found in normal but once active galaxies. Based on the properties of a few such "post-active" galaxies that are representative for a much wider group, it has been argued that they have reached the evolutionary stages when their nuclei, which were radio-loud in the past, now, mimicking the behaviour of XRBs, remain in the intermediate state on their way towards quiescence or even have already entered the quiescent state. It follows that the full evolutionary track of XRBs can be mapped onto the evolution of galaxies. The above findings are in line with those reported recently for IC 2497, a galaxy that 70,000 years ago or less hosted a quasar but now appears as a normal one. This scenario stems from the presence of Hanny's Voorwerp, a nebulous object in its vicinity excited by that QSO in the epoch when IC 2497 was active. The post-active galaxies we deal with here are accompanied by extremely weak and diffuse relic radio lobes that were inflated during their former active period. These relics can be regarded as radio analogues of Hanny's Voorwerp.Comment: 10 pages, 6 figures, A&A in pres

Relativistic MHD Simulations of Jets with Toroidal Magnetic Fields

This paper presents an application of the recent relativistic HLLC approximate Riemann solver by Mignone & Bodo to magnetized flows with vanishing normal component of the magnetic field. The numerical scheme is validated in two dimensions by investigating the propagation of axisymmetric jets with toroidal magnetic fields. The selected jet models show that the HLLC solver yields sharper resolution of contact and shear waves and better convergence properties over the traditional HLL approach.Comment: 12 pages, 5 figure