Issue |
A&A
Volume 468, Number 1, June II 2007
|
|
---|---|---|
Page(s) | 193 - 203 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20041285 | |
Published online | 29 March 2007 |
Simulation of the interstellar scintillation and the extreme scattering events of pulsars
1
LPCE/CNRS, 3A Av. de la Recherche Scientifique, 45071 Orléans, France
2
Astronomy Department, University of Illinois at Urbana-Champaign, 1002 W Green St, Urbana, IL 61801, USA e-mail: mhamidou@astro.uiuc.edu
3
LERMA/CNRS, Observatoire de Paris, 77 Av. Denfert Rochereau, 75014 Paris, France e-mail: jean-francois.lestrade@obspm.fr
Received:
13
May
2004
Accepted:
10
March
2007
The rare and conspicuous flux density variations of some radio sources (extragalactic and pulsars)
for periods of weeks to months have been denoted Extreme Scattering Events (ESE's) by Fiedler et al. (1987, Nature, 362, 675).
Presently, there is no astrophysical mechanism that satisfactorily produces
this phenomenon. In this paper, we conjecture that inhomogeneities of the
electronic density in the turbulent interstellar medium might be the origin of this phenomenon. We
have tested this conjecture by a simulation of the scintillation of the pulsar B1937+21 at 1.4 GHz and 1.7 GHz for a period of six months. To this end,
we have constructed a large square Kolmogorov phase screen made of
pixels with electron inhomogeneity scales
ranging from
to
and used the Kirchhoff-Fresnel integral to simulate dynamic
spectra of a pulsar within the framework of Physical Optics.
The simulated light curves exhibit a 10 day long variation
simultaneously at 1.41 and 1.7 GHz that is alike
the “ESE” observed with the Nançay radiotelescope toward the pulsar B1937+21 in October 1989.
Thus, we conclude that the “ESE” toward pulsars
can be caused naturally by the turbulence in the
ionized interstellar medium. This is instead of
discrete over pressured ionized clouds crossing the line of sight
as in the model of Fiedler et al. (1987, Nature, 362, 675). We suggest that longer
events could occur in a simulation of scintillation,
if larger electron inhomogeneities
were
included in the construction of the Kolmogorov phase screen. This next step
requires a supercomputer.
Key words: scattering / turbulence / ISM: structure / stars: pulsars: general
© ESO, 2007
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