Presentation 1 : Oral
Simulation of ESE's in the turbulent ionised ISM
Hamidouche, A.M, Lestrade, J-F and Cognard, I
Extreme Scattering Events (ESE's) in directions of extragalactic sources and pulsars are rare events that have been interpreted as discrete clouds of plasma crossing the line of sights and acting as lenses. The observations lead to a model implying that these clouds are short lived and that their space density is as high as $\sim 10^6 pc^{-3}$ clouds in the Galaxy. These implications are usually difficult to reconcile with our current view of the interstellar medium.
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We have explored an alternative model. It is well known that the ionised interstellar medium is turbulent and that its inhomogeneities of the electronic density closely match the Kolmogorov 3D spatial spectrum. We have simulated scintillation produced by such a spectrum in the thin screen approximation. The simulation of the corresponding 2D phase screen for 16 years of observations of pulsars at Nancay is modelled by 17 Gigapixels. This has been a challenge numerically. Scintillation (flux density variation) calculation for a point source (pulsar) is carried out with the kirchhoff-Fresnel integral in the framework of physical optics. We show that our model does exhibit ESE's over 16 years at a rate (number of ESE's per year) that is consistent with the observed rate at Nancay. Consequently, we propose that turbulence in the ionised ISM be the natural source for ESE's in directions of pulsars.
Presentation 2 : Poster
Simulation of ESE's in the turbulent ionised ISM
Hamidouche, A.M, Lestrade, J-F and Cognard, I
Extreme Scattering Events (ESE's) in directions of extragalactic sources and pulsars are rare events that have been interpreted as discrete clouds of plasma crossing the line of sights and acting as lenses. The observations lead to a model implying that these clouds are short lived and that their space density is as high as $\sim 10^6 pc^{-3}$ clouds in the Galaxy. These implications are usually difficult to reconcile with our current view of the interstellar medium.
\\
We have explored an alternative model. It is well known that the ionised interstellar medium is turbulent and that its inhomogeneities of the electronic density closely match the Kolmogorov 3D spatial spectrum. We have simulated scintillation produced by such a spectrum in the thin screen approximation. The simulation of the corresponding 2D phase screen for 16 years of observations of pulsars at Nancay is modelled by 17 Gigapixels. This has been a challenge numerically. Scintillation (flux density variation) calculation for a point source (pulsar) is carried out with the kirchhoff-Fresnel integral in the framework of physical optics. We show that our model does exhibit ESE's over 16 years at a rate (number of ESE's per year) that is consistent with the observed rate at Nancay. Consequently, we propose that turbulence in the ionised ISM be the natural source for ESE's in directions of pulsars.