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Dive into the research topics where Antonios Nathanail is active.

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Featured researches published by Antonios Nathanail.


The Astrophysical Journal | 2014

Black Hole Magnetospheres

Antonios Nathanail; Ioannis Contopoulos

We investigate the structure of the steady-state force-free magnetosphere around a Kerr black hole in various astrophysical settings. The solution Ψ(r, θ) depends on the distributions of the magnetic field line angular velocity ω(Ψ) and the poloidal electric current I(Ψ). These are obtained self-consistently as eigenfunctions that allow the solution to smoothly cross the two singular surfaces of the problem, the inner light surface inside the ergosphere, and the outer light surface, which is the generalization of the pulsar light cylinder. Magnetic field configurations that cross both singular surfaces (e.g., monopole, paraboloidal) are uniquely determined. Configurations that cross only one light surface (e.g., the artificial case of a rotating black hole embedded in a vertical magnetic field) are degenerate. We show that, similar to pulsars, black hole magnetospheres naturally develop an electric current sheet that potentially plays a very important role in the dissipation of black hole rotational energy and in the emission of high-energy radiation.


The Astrophysical Journal | 2015

The Cosmic Battery in Astrophysical Accretion Disks

Ioannis Contopoulos; Antonios Nathanail; Matthaios Katsanikas

The aberrated radiation pressure at the inner edge of the accretion disk around an astrophysical black hole imparts a relative azimuthal velocity on the electrons with respect to the ions which gives rise to a ring electric current that generates large scale poloidal magnetic field loops. This is the Cosmic Battery established by Contopoulos and Kazanas in 1998. In the present work we perform realistic numerical simulations of this important astrophysical mechanism in advection-dominated accretion flows-ADAF. We confirm the original prediction that the inner parts of the loops are continuously advected toward the central black hole and contribute to the growth of the large scale magnetic field, whereas the outer parts of the loops are continuously diffusing outward through the turbulent accretion flow. This process of inward advection of the axial field and outward diffusion of the return field proceeds all the way to equipartition, thus generating astrophysically significant magnetic fields on astrophysically relevant timescales. We confirm that there exists a critical value of the magnetic Prandtl number between unity and 10 in the outer disk above which the Cosmic Battery mechanism is suppressed.


Monthly Notices of the Royal Astronomical Society | 2016

The rapid decay phase of the afterglow as the signature of the Blandford–Znajek mechanism

Antonios Nathanail; Achillies Strantzalis; Ioannis Contopoulos

Gamma-ray bursts (GRBs) are believed to be powered by the electromagnetic extraction of spin energy from a black hole endowed with a magnetic field supported by electric currents in a surrounding disk (Blandford & Znajek 1977). A generic feature of this mechanism is that, under certain fairly general assumptions, the energy loss rate decays exponentially. In this work, we are looking precisely for such exponential decay in the lightcurves of long duration GRBs observed with the XRT instrument on the Swift satellite. We found out that almost 30 % of XRT lightcurves show such behavior before they reach the afterglow plateau. According to Blandford & Znajek, the duration of the burst depends on the magnetic flux accumulated on the event horizon. This allows us to estimate the surface magnetic field of a possible progenitor. Our estimations are consistent with magnetic fields observed in Wolf-Rayet stars.


The Astrophysical Journal | 2013

THE ORTHOGONAL GAMMA-RAY BURST MODEL

Ioannis Contopoulos; Antonios Nathanail; Daniela Pugliese

We explore the analogy between a rotating magnetized black hole and an axisymmetric pulsar and derive the black holes electromagnetic spindown after its formation in the core collapse of a supermassive star. The spindown shows two characteristic phases: an early Blandford-Znajek phase that lasts a few hundred seconds and a late pulsar-like afterglow phase that lasts much longer. During the first phase, the spindown luminosity decreases almost exponentially, whereas during the afterglow phase it decreases as t –a with 1 a 1.5. We associate our findings with long duration gamma-ray bursts and compare them with observations.


arXiv: High Energy Astrophysical Phenomena | 2015

Black Hole Spin Down in GRB observations and cosmology

Antonios Nathanail; Ioannis Contopoulos; Spyros Basilakos

According to Blandford & Znajek (1977), energy can be extracted electromagnetically from a rotating black hole, should the latter be endowed with a magnetic field supported by electric currents in a surrounding disk. We show that exact models of black hole magnetospheres produce Poynting flux that decreases almost exponentially with time. We went through the Swift BAT-XRT lightcurves and identified a subclass of GRBs that exhibits a clear exponential decay over more than three orders of magnitude in flux (EDOHS GRBs). We estimate the energy given-off in the X-rays and discuss a possible correlation between the peak brightness of the X-ray prompt emission and its decay time. We investigate a possible application of this result in high redshift Cosmology.


The Astrophysical Journal | 2018

An Explosion is Triggered by the Late Collapse of the Compact Remnant from a Neutron Star Merger

Antonios Nathanail

It is known that a binary neutron star merger produces a hypermassive neutron star. The lifetime of this compact remnant depends on the total mass and the equation of state. The collapse of this compact remnant to a black- hole-torus system is expected to give rise to a powerful jet and a short gamma-ray burst. Nevertheless, if the collapse is delayed half a second or so, the surrounding matter would be already accreted and/or expelled and hence no torus will be formed. However, the collapse itself will give rise to a quasi-isotropic magnetized fireball. This magnetic bomb will dissipate much of its energy due to magnetic re-connection and will produce the prompt emission, when the fireball will become transparent to gamma-rays. The energy range of such an explosion depends on the initial magnetic field strength of the two neutron stars and the amplification of the magnetic energy during merger. We discuss the production of a quasi-isotropic magnetized fireball and its subsequent interaction with the ejected matter during merger, as the outcome of the coalescence of a binary neutron star system. We further discuss a possible origin for the duration of the burst and the radial stratification of the flow following the quasi-normal modes of the black hole.


Monthly Notices of the Royal Astronomical Society | 2015

Are ultralong gamma-ray bursts powered by black holes spinning down?

Antonios Nathanail; Ioannis Contopoulos


Galaxies | 2017

The Signature of the Blandford-Znajek Mechanism in GRB Light Curves

Ioannis Contopoulos; Antonios Nathanail; Achillies Strantzalis


arXiv: High Energy Astrophysical Phenomena | 2018

Binary neutron star and short gamma-ray burst simulations in light of GW170817

Antonios Nathanail


arXiv: High Energy Astrophysical Phenomena | 2018

The collapse of the remnant from a binary neutron star merger powers a magnetic explosion: implication to short gamma-ray bursts

Antonios Nathanail

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Armen Sedrakian

Goethe University Frankfurt

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Arus Harutyunyan

Goethe University Frankfurt

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Luciano Rezzolla

Frankfurt Institute for Advanced Studies

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