VLBI Imaging Of Interstellar Scattering With A Resolution Of 0.1 Mas ( 0.05 A.u.).
Abstract
We have invented a novel technique that combines VLBI astrometry with observations of parabolic arcs in the secondary spectrum of pulsars as discovered by Stinebring et al (2001). The secondary spectrum technique allows us to isolate each scattered component of the angular spectrum by its delay and doppler shift. Observing the "visibility secondary spectrum", we can use astrometry to locate each of these scattered components individually. This can be done with much higher resolution than one would obtain with a conventional VLBI image using the same baselines. This reconstruction technique is applicable when the scattering is highly anisotropic. We present observations of the pulsar B0834+06 at 320 MHz. The primary image is highly elongated, having an extent of 20 mas and an axial ratio >75. It is deeply modulated along its axis on scales as small as 0.1 mas ( 0.05 A.U.). There is a secondary feature off the main scattering axis by about 20 mas, which may be related to ``Extreme Scattering Events''. By comparing the astrometry with the scattered delay and doppler shifts we can measure the distance and velocity of each point in the scattering region. The distance is about 400 pc and the apparent velocity is dominated by the pulsar proper motion. The proper motion is not (yet) known well enough to obtain an accurate measurement of the plasma velocity. Two possible scenarios for the highly anisotropic scattering will be described, both of which rely on alignment by a magnetic field.
Scintillation research at UCSD is funded by the NSF (AST 0507713)- Publication:
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American Astronomical Society Meeting Abstracts #214
- Pub Date:
- May 2009
- Bibcode:
- 2009AAS...21442904R