Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Orientation of the crescent image of M 87*   The first image of the black hole (BH) M 87* obtained by the Event Horizon
Telescope (EHT) has the shape of a crescent extending from the E to WSW
position angles, while the observed direction of the large-scale jet is WNW.
Images based on numerical simulations of BH accretion flows suggest that on
average the projected BH spin axis should be oriented SSW. We explore highly
simplified toy models for geometric distribution and kinematics of emitting
regions in the Kerr metric, perform ray tracing to calculate the corresponding
images, and simulate their observation by the EHT to calculate the
corresponding visibilities and closure phases. We strictly assume that (1) the
BH spin vector is fixed to the jet axis, (2) the emitting regions are
stationary and symmetric with respect to the BH spin, and that (3) the
emissivities are isotropic in the local rest frames. Emission from the crescent
sector between SSE and WSW can be readily explained in terms of an equatorial
ring with either circular or plunging geodesic flows, regardless of the value
of BH spin. In the case of plane-symmetric polar caps with plunging geodesic
flows, the dominant image of the cap located behind the BH is sensitive to the
angular momentum of the emitter. Within the constraints of our model, we have
not found a viable explanation for the observed brightness of the ESE sector.
Most likely, the ESE "hotspot" has been produced by a non-stationary localised
perturbation in the inner accretion flow. Alternatively, it could result from
locally anisotropic synchrotron emissivities. Multi-epoch and polarimetric
results from the EHT will be essential to verify the theoretically expected
alignment of the BH spin with the large-scale jet.

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The categories of this paper are: cs
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: bayes-an
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex