Image of the Janis-Newman-Winicour naked singularity with a thin accretion disk. (arXiv:1905.05273v1 [gr-qc])

Image of the Janis-Newman-Winicour naked singularity with a thin accretion disk. (arXiv:1905.05273v1 [gr-qc])
<a href="http://arxiv.org/find/gr-qc/1/au:+Gyulchev_G/0/1/0/all/0/1">Galin Gyulchev</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Nedkova_P/0/1/0/all/0/1">Petya Nedkova</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Vetsov_T/0/1/0/all/0/1">Tsvetan Vetsov</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Yazadjiev_S/0/1/0/all/0/1">Stoytcho Yazadjiev</a>

We study the optical appearance and the apparent radiation flux of a thin
accretion disk around the static Janis-Newman-Winicour naked singularity. We
confine ourselves to the astrophysically most relevant case, when the solution
possesses a photon sphere, assuming that the radiation emitted by the disk is
described by the Novikov-Thorne model. The observable images resemble closely
the visual appearance of the Schwarzschild black hole, as only quantitative
differences are present. For the Janis-Newman-Winicour solution the accretion
disk appears smaller, and its emission is characterized by a higher peak of the
radiation flux. In addition, the most significant part of the radiation is
concentrated in a closer neighbourhood of the flux maximum. The results are
obtained independently by two alternative methods, consisting of a
semi-analytical scheme using the spherical symmetry of the spacetime, and a
fully numerical ray-tracing procedure valid for any stationary and axisymmetric
spacetime.

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