Imprints of the Janis-Newman-Winicour spacetime on observations related
  to shadow and accretion
  The final fate of gravitational collapse of massive stars has been a subject
of interest for a long time since such a collapse may lead to black holes and
naked singularities alike. Since, the formation of naked singularities is
forbidden by the cosmic censorship conjecture, exploring their observational
differences from black holes may be a possible avenue to search for these
exotic objects. The simplest possible naked singularity spacetime emerges from
the Einstein massless scalar field theory with the advantage that it smoothly
translates to the Schwarzschild solution by the variation of the scalar charge.
This background, known as the Janis-Newman-Winicour spacetime is the subject of
interest in this work. %A further advantage of working with this spacetime is
that it smoothly translates to the Schwarzschild solution by the variation of
the scalar charge. We explore electromagnetic observations around this metric
which involves investigating the characteristics of black hole accretion and
shadow. We compute the shadow radius in this spacetime and compare it with the
image of M87*, recently released by the Event Horizon Telescope Collaboration.
Similarly, we derive the expression for the luminosity from the accretion disk
and compare it with the observed optical luminosity of eleven Palomar Green
quasars. Our analysis indicates that the shadow of M87* and the quasar optical
data consistently favor the Schwarzschild background over the
Janis-Newman-Winicour spacetime. The implications of this result are discussed.
