The dynamic spectral signatures from Lunar Occultation: A simulation study. (arXiv:1811.12714v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Patel_J/0/1/0/all/0/1">Jigisha V. Patel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Deshpande_A/0/1/0/all/0/1">Avinash A. Deshpande</a>
Lunar occultation, which occurs when the Moon crosses sight-lines to distant
sources, has been studied extensively through apparent intensity pattern
resulting from Fresnel diffraction, and has been successfully used to measure
angular sizes of extragalactic sources. However, such observations to-date have
been mainly over narrow bandwidth, or averaged over the observing band, and the
associated intensity pattern in time has rarely been examined in detail as a
function of frequency over a wide band. Here, we revisit the phenomenon of
lunar occultation with a view to study the associated intensity pattern as a
function of both time and frequency. Through analytical and simulation
approach, we examine the variation of intensity across the dynamic spectra, and
look for chromatic signatures which could appear as discrete dispersed signal
tracks, when the diffraction pattern is adequately smoothed by a finite source
size. We particularly explore circumstances in which such diffraction pattern
might closely follow the interstellar dispersion law followed by pulsars and
transients, such as the Fast Radio Bursts (FRBs), which remain a mystery even
after a decade of their discovery. In this paper, we describe details of this
investigation, relevant to radio frequencies at which FRBs have been detected,
and discuss our findings, along with their implications. We also show how a
band-averaged light curve suffers from temporal smearing, and consequent
reduction in contrast of intensity variation, with increasing bandwidth. We
suggest a way to recover the underlying diffraction signature, as well as the
sensitivity improvement commensurate with usage of large bandwidths.
Lunar occultation, which occurs when the Moon crosses sight-lines to distant
sources, has been studied extensively through apparent intensity pattern
resulting from Fresnel diffraction, and has been successfully used to measure
angular sizes of extragalactic sources. However, such observations to-date have
been mainly over narrow bandwidth, or averaged over the observing band, and the
associated intensity pattern in time has rarely been examined in detail as a
function of frequency over a wide band. Here, we revisit the phenomenon of
lunar occultation with a view to study the associated intensity pattern as a
function of both time and frequency. Through analytical and simulation
approach, we examine the variation of intensity across the dynamic spectra, and
look for chromatic signatures which could appear as discrete dispersed signal
tracks, when the diffraction pattern is adequately smoothed by a finite source
size. We particularly explore circumstances in which such diffraction pattern
might closely follow the interstellar dispersion law followed by pulsars and
transients, such as the Fast Radio Bursts (FRBs), which remain a mystery even
after a decade of their discovery. In this paper, we describe details of this
investigation, relevant to radio frequencies at which FRBs have been detected,
and discuss our findings, along with their implications. We also show how a
band-averaged light curve suffers from temporal smearing, and consequent
reduction in contrast of intensity variation, with increasing bandwidth. We
suggest a way to recover the underlying diffraction signature, as well as the
sensitivity improvement commensurate with usage of large bandwidths.
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