Orbital motion near Sagittarius A* -- Constraints from polarimetric ALMA observations

Abstract

We report on the polarized light curves of the Galactic Center supermassive black hole Sagittarius A*, obtained at millimeter wavelength with the Atacama Large Millimeter/submillimeter Array (ALMA). The observations took place as a part of the Event Horizon Telescope campaign. We compare the observations taken during the low variability source state on 2017 Apr 6 and 7 with those taken immediately after the X-ray flare on 2017 Apr 11. For the latter case, we observe rotation of the electric vector position angle with a timescale of $\sim 70$ min. We interpret this rotation as a signature of the equatorial clockwise orbital motion of a hot spot embedded in a magnetic field dominated by a dynamically important vertical component, observed at a low inclination $\sim 20^{\circ }$. The hot spot radiates strongly polarized synchrotron emission, briefly dominating the linear polarization measured by ALMA in the unresolved source. Our simple emission model captures the overall features of the polarized light curves remarkably well. Assuming a Keplerian orbit, we find the hot spot orbital radius to be $\sim$ 5 Schwarzschild radii. We observe hints of a positive black hole spin, that is, a prograde hot spot motion. Accounting for the rapidly varying rotation measure, we estimate the projected on-sky axis of the angular momentum of the hot spot to be $\sim 60^{\circ }$ east of north, with a 180${}^{\circ }$ ambiguity. These results suggest that the accretion structure in Sgr A* is a magnetically arrested disk rotating clockwise.

References in corpus (29)

• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon
• First Sagittarius A* Event Horizon Telescope Results. VI: Testing the Black Hole Metric
• First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
• First M87 Event Horizon Telescope Results. VII. Polarization of the Ring
• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass
• The mass distribution in the Galactic Centre from interferometric astrometry of multiple stellar orbits
• Black hole flares: ejection of accreted magnetic flux through 3D plasmoid-mediated reconnection
• Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks
• Polarimetry of near-infrared flares from Sagittarius A*
• Flares in the Galactic center I: orbiting flux tubes in Magnetically Arrested Black Hole Accretion Disks
• Modeling the orbital motion of Sgr A*'s near-infrared flares
• Sgr A* near-infrared flares from reconnection events in a magnetically arrested disc
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Polarimetric properties of Event Horizon Telescope targets from ALMA
• Time Dependent Models of Flares from Sagittarius A*
• The Polarized Image of a Synchrotron Emitting Ring of Gas Orbiting a Black Hole
• Polarized Image of Equatorial Emission in the Kerr Geometry
• The Submillimeter Polarization of Sgr A*
• Dynamically important magnetic fields near the event horizon of Sgr A*
• Calibration of ALMA as a phased array: ALMA observations during the 2017 VLBI campaign
• Resolving the inner parsec of the blazar J1924-2914 with the Event Horizon Telescope
• Spacetime Tomography Using The Event Horizon Telescope
• The origin of hotspots around Sgr A*: Orbital or pattern motion?
• A first search of transients in the Galactic Center from 230 GHz ALMA observations

Cited by in corpus (44)

• Key Science Goals for the Next-Generation Event Horizon Telescope
• Polarimetry and Astrometry of NIR Flares as Event Horizon Scale, Dynamical Probes for the Mass of Sgr A*
• First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization
• Polarimetric signatures of hot spots in black hole accretion flows
• Photon Ring Astrometry for Superradiant Clouds
• Magnetic reconnection plasmoid model for Sagittarius A* flares
• Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode
• Observational Appearances of Magnetically Charged Black Holes in Born-Infeld Electrodynamics
• Using Machine Learning to Link Black Hole Accretion Flows with Spatially Resolved Polarimetric Observables
• Demonstrating Photon Ring Existence with Single-Baseline Polarimetry
• The internal Faraday screen of Sagittarius A*
• Two-Temperature GRMHD Simulations of Black Hole Accretion Flows with Multiple Magnetic Loops
• Ordered magnetic fields around the 3C 84 central black hole
• Fitting the light curves of Sagittarius A* with a hot-spot model
• Accretion Flow Morphology in Numerical Simulations of Black Holes from the ngEHT Model Library: The Impact of Radiation Physics
• Rotation in Event Horizon Telescope Movies
• General relativistic hydrodynamic simulations of perturbed transonic accretion
• Detecting Axion Dark Matter with Black Hole Polarimetry
• General relativistic effects and the near-infrared and X-ray variability of Sgr A* I
• Shadows near supermassive black holes: from a theoretical concept to GR test
• The Relationship Between Simulated Sub-Millimeter and Near-Infrared Images of Sagittarius A* from a Magnetically Arrested Black Hole Accretion Flow
• How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models
• Hot-spots around Sagittarius A*: Joint fits to astrometry and polarimetry
• Relativistic Signatures of Flux Eruption Events Near Black Holes
• Dusty plasma in active galactic nuclei
• Dynamics and Emission Properties of Flux Ropes from Two-Temperature GRMHD Simulations with Multiple Magnetic Loops
• Polarized signatures of adiabatically expanding hotspots in Sgr A*'s accretion flow
• Forward Ray Tracing and Hot Spots in Kerr Spacetime
• Expanding Sgr A* dynamical imaging capabilities with an African extension to the Event Horizon Telescope
• Deep learning inference with the Event Horizon Telescope III. Zingularity results from the 2017 observations and predictions for future array expansions
• General Relativistic effects and the NIR variability of Sgr A* II: A systematic approach to temporal asymmetry
• Monitoring the Size and Flux Density of Sgr A* during the Active State in 2019 with East Asian VLBI Network
• Dark Matter reconstruction from stellar orbits in the Galactic Centre
• A kinetic model of jet-corona coupling in accreting black holes
• Non-thermal Synchrotron Emission and Polarization Signatures during Black Hole Flux Eruptions
• Energy distribution and substructure formation in astrophysical MHD simulations
• Strong gravitational lensing of a five-dimensional charged, equally rotating black hole with a cosmological constant
• Characterization of black hole accretion through image moment invariants
• Photometric Constraints on Intermediate-mass Black Holes in the Galactic Centre
• Polarization Signatures of Inspiraling Hotspots around Kerr Black Holes
• Variability of Sagittarius A* at 3 GHz on minute-scale with MeerKAT
• Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign
• High Energy Emission from the Galactic Center
• Sagittarius A* near-infrared flares polarization as a probe of space-time I: Non-rotating exotic compact objects