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Searching for Structural Variability in Sgr A*
Author(s) -
Shen ZhiQiang,
Liang M. C.,
Lo K. Y.,
Miyoshi M.
Publication year - 2003
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.200385090
Subject(s) - very long baseline interferometry , amplitude , very long baseline array , physics , millimeter , wavelength , calibration , epoch (astronomy) , astrophysics , geology , geodesy , astronomy , active galactic nucleus , optics , galaxy , quantum mechanics
A model fitting procedure for estimating the parameters of an elliptical Gaussian model that describes the radio emission of Sgr A* observed by the VLBA is presented. By (implicitly) using the amplitude closure relation while fitting the amplitude, the procedure can minimize the calibration errors in millimeter wavelength VLBI measurements, which are crucial to our ongoing effort to search for the structural variability in Sgr A*. The preliminary results from the application to seven‐epoch λ 7mm VLBA observations seem to show the sign of change to the source apparent structure in at least one epoch over the period of 7 years (1994–2001). Because of the large uncertainties in the determination of minor axis caused mainly by the poor spatial resolution along the north‐south direction with the VLBA, these results are suggestive but not conclusive. This demonstrates the necessity of adding the NRAO GBT antenna to the future λ 7mm VLBA observations, which can greatly improve the resolution in the north‐south by a factor of 3.