Experience of high resolution VLBI imaging using generalized maximum entropy method

Details Experience of high resolution VLBI imaging using generalized maximum entropy method Experience of high resolution VLBI imaging using generalized maximum entropy method

2002-04-18

arxiv.org/abs/astro-ph/0204312v1

Astron. & Astroph. Tr. 20 (2001) 393-403

Astronomy and Astrophysics

Astrophysics

Latex, 11 pages with 4 Postscript figures (images of 36 extragalactic radio sources)

Scientific paper

The generalized maximum entropy method (GMEM) is a special modification of the standard maximum entropy method (MEM) which seeks solutions in the space of complex functions. In this work a reduced version of the GMEM intended for reconstructing real images with positive and negative values is used. As compared with the standard MEM, intended for the reconstruction of only non-negative images, the GMEM allows us to obtain higher-quality images with a much lower level of nonlinear distortions caused by errors in the data. Here, we present the results of the GMEM imaging of 36 selected extragalactic radio sources with a resolution of 0.3-0.5 mas on astrometric and geodetic VLBI observations at 8.2 GHz, obtained with a global array in the period from 1994-1996. In VLBI mapping practice this is the first experience of imaging with such a high resolution using maximum entropy technique. A differential maximum entropy method intended for increasing the dynamic range of images is demonstrated on the radio source 0059+581. In the case of unreliable `closure' phases, completely `phaseless' methods of mapping are recommended. Maps of two sources 0615+820 and 0642+214 are obtained using one such method.

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