5th of May 2016 |
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Monitoring the Galactic Centre with the ATCA |
by Abhijeet Borkar (Universität Köln; Germany) |
The supermassive black hole, Sagittarius A*
(Sgr A*), at the centre of the Milky Way undergoes regular flaring activity,
which is thought to arise from the innermost region of the accretion flow.
Between 2010 and 2014, we performed monitoring observations of the Galactic
Centre to study the flux-density variations at 3 mm using the Australia
Telescope Compact Array (ATCA). We obtain light curves of Sgr A* by
subtracting the contributions from the extended emission around it,
and the elevation and time-dependent gains of the telescope. We
perform structure function analysis and the Bayesian blocks
representation to detect flare events. The observations detect six
instances of significant variability in the flux density of Sgr A* in
three observations, with variations between 0.5 and 1.0 Jy, which last
for 1.5-3 h. We use the adiabatically expanding plasmon model to
explain the short time-scale variations in the flux density. We derive
the physical quantities of the modelled flare emission, such as the
source expansion speed v_exp, source sizes, spectral indices and the
turnover frequency. These parameters imply that the expanding source
components are either confined to the immediate vicinity of Sgr A* by
contributing to the corona or the disc, or have a bulk motion greater
than v_exp . No exceptional flux-density variation on short flare
time-scales was observed during the approach and the flyby of the
dusty S-cluster object (DSO/G2). This is consistent with its
compactness and the absence of a large bow shock. Reference: Borkar, A., et al. 2016, MNRAS 458, 2336 |