Prospects for testing the nature of Sgr A*'s NIR flares on the basis of current VLT- and future VLTI-observations

Abstract

Sagittarius A*, the supermassive compact object at the center of the Galaxy, exhibits outbursts in the near infrared and X-ray domains. These flares are likely due to energetic events very close to the central object, on a scale of a few Schwarzschild radii. Optical interferometry will soon be able to provide astrometry with an accuracy of this order (~10 muas). In this article we use recent photometric near infrared data observed with the adaptive optics system NACO at the Very Large Telescope combined with simulations in order to deploy a method to test the nature of the flares and to predict the possible outcome of observations with the Very Large Telescope Interferometer. To accomplish this we implement a hot spot model and investigate its appearance for a remote observer in terms of light curves and centroid tracks, based on general relativistic ray tracing methods. First, we use a simplified model of a small steady source in order to investigate the relativistic effects qualitatively. A more realistic scenario is then being developed by fitting our model to existing flare data. While indications for the spin of the black hole and multiple images due to lensing effects are marginal in the light curves, astrometric measurements offer the possibility to reveal these high-order general relativistic effects. This study makes predictions on these astrometric measurements and leads us to the conclusion that future infrared interferometers will be able to detect proper motion of hot spots in the vicinity of Sagittarius A*.

15 pages, 14 figures, accepted for publication in ApJ

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• Observing gravitational lensing effects by Sgr A* with GRAVITY
• Adaptive Analytical Ray Tracing of Black Hole Photon Rings
• Spectral and Imaging properties of Sgr A* from High-Resolution 3D GRMHD Simulations with Radiative Cooling
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• Polarimetric signatures of hot spots in black hole accretion flows
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• Magnetic reconnection plasmoid model for Sagittarius A* flares
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• Testing the nature of the supermassive black hole candidate in SgrA* with light curves and images of hot spots
• Relative Astrometry of Compact Flaring Structures in Sgr A* with Polarimetric VLBI
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• Study of the X-ray activity of Sgr A* during the 2011 XMM-Newton campaign
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• Hot-spots around Sagittarius A*: Joint fits to astrometry and polarimetry
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• General Relativistic effects and the NIR variability of Sgr A* II: A systematic approach to temporal asymmetry
• Possible evidence from the flaring activity of Sgr A* for a star at a distance of ~3.3 Schwarzscild radii from the blackhole
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• Investigating non-Keplerian motion in flare events with astrometric data
• The orbit and nature of the semi-detached stellar companion of Sgr A* super-massive blackhole
• Sagittarius A* near-infrared flares polarization as a probe of space-time I: Non-rotating exotic compact objects