Testing the TDE Outflow Model for the Bipolar Sgr A Lobes at the Galactic Center
arxiv(2024)
摘要
Sgr A lobes are a pair of 15-pc-sized bipolar bubbles with co-aligned major
axes perpendicular to the Galactic plane found in X-ray and radio observations
of the Galactic center (GC). Their elusive origin is a vital ingredient in
understanding the ongoing high energy processes at the GC. Here we perform a
suite of hydrodynamic simulations to explore the tidal disruption event (TDE)
outflow model for the origin of the Sgr A lobes. By following the outflow
evolution in the circumnuclear medium, we find that TDE outflows naturally
produce bipolar lobes delimited by forward shocks, and the dense postshock
shell contributes significantly to the lobe's X-ray emission. Our fiducial run
reproduces the morphology, density, temperature, and X-ray surface brightness
distribution of the observed Sgr A lobes reasonably well. The current lobe age
is 3300 yr. Our model further predicts that the uplifted wake flow breaks
through the ejecta-induced shock front, producing a shock-enclosed head region
which is relatively dim in X-rays compared to other lobe regions. Both the dim
head region and the predicted limb-brightening feature of the lobes are
slightly inconsistent with current X-ray observations, and may be used to
further test our model with more sensitive future X-ray observations. While
light narrow jets and massive wide winds from TDE events usually do not
reproduce the observed oval-shaped morphology of the lobes, the TDE outflow in
our fiducial run is massive and yet narrow. Whether it is a jet or wind remains
uncertain and future simulations covering both the outflow acceleration region
and its pc-scale evolution would be very helpful in determining whether the Sgr
A lobes indeed originate from a pair of TDE jets or winds.
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