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Micro-arcsecond structure of Sagittarius A* revealed by high-sensitivity 86 GHz VLBI observations | | Christiaan D. Brinkerink
; Cornelia Müller
; Heino D. Falcke
; Sara Issaoun
; Kazunori Akiyama
; Geoffrey C. Bower
; Thomas P. Krichbaum
; Adam T. Deller
; Edgar Castillo
; Sheperd S. Doeleman
; Raquel Fraga-Encinas
; Ciriaco Goddi
; Antonio Hernández-Gómez
; David H. Hughes
; Michael Kramer
; Jonathan Léon-Tavares
; Laurent Loinard
; Alfredo Montaña
; Monika Mościbrodzka
; Gisela N. Ortiz-León
; David Sanchez-Arguelles
; Remo P. J. Tilanus
; Grant W. Wilson
; J. Anton Zensus
; | | Date: |
20 Nov 2018 | | Abstract: | The compact radio source Sagittarius~A$^*$ (Sgr~A$^*$)in the Galactic Center
is the primary supermassive black hole candidate. General relativistic
magnetohydrodynamical (GRMHD) simulations of the accretion flow around
Sgr,A$^*$ predict the presence of sub-structure at observing wavelengths of
$sim 3$,mm and below (frequencies of 86,GHz and above). For very long
baseline interferometry (VLBI) observations of Sgr,A$^*$ at this frequency the
blurring effect of interstellar scattering becomes subdominant, and arrays such
as the High Sensitivity Array (HSA) and the global mm-VLBI Array (GMVA) are now
capable of resolving potential sub-structure in the source. Such investigations
improve our understanding of the emission geometry of the mm-wave emission of
Sgr,A$^*$, which is crucial for constraining theoretical models and for
providing a background to interpret 1,mm VLBI data from the Event Horizon
Telescope (EHT). We performed high-sensitivity very long baseline
interferometry (VLBI) observations of Sgr,A$^*$ at 3,mm using the Very Long
Baseline Array (VLBA) and the Large Millimeter Telescope (LMT) in Mexico on two
consecutive days in May 2015, with the second epoch including the Green Bank
Telescope (GBT). We find an overall source geometry that matches previous
findings very closely, showing a deviation in fitted model parameters less than
3\% over a time scale of weeks and suggesting a highly stable global source
geometry over time. The reported sub-structure in the 3,mm emission of
Sgr,A$^*$ is consistent with theoretical expectations of refractive noise on
long baselines. However, comparing our findings with recent results from 1,mm
and 7,mm VLBI observations, which also show evidence for east-west asymmetry,
an intrinsic origin cannot be excluded. Confirmation of persistent intrinsic
substructure will require further VLBI observations spread out over multiple
epochs. | | Source: | arXiv, 1811.8394 | | Services: | Forum | Review | PDF | Favorites | |
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