Polarimetric signatures of hot spots in black hole accretion flows

Abstract

The flaring events observed in the Sagittarius A* supermassive black hole system can be attributed to the non-homogeneous nature of the near-horizon accretion flow. Bright regions in this flow may be associated with density or temperature anisotropies, so-called "bright spot" or "hot spots". Such orbiting features may explain observations at infrared wavelengths as well as recent findings at millimeter wavelengths. In this work, we study the emission from an orbiting equatorial bright spot, imposed on a radiatively inefficient accretion flow background, to find polarimetric features indicative of the underlying magnetic field structure and other system variables including inclination angle, spot size, black hole spin, and more. Specifically, we investigate the impact of these parameters on the Stokes Q-U signatures that commonly exhibit a typical double loop (pretzel-like) structure. Our semi-analytical model, describing the underlying plasma conditions and the orbiting spot, is built within the framework of the numerical radiative transfer code ipole, which calculates synchroton emission at 230 GHz. We showcase the wide variety of Q-U loop signatures and the relation between inner and outer loops. For the vertical magnetic field topology, the inner Q-U loop is explained by the suppression of the synchrotron emission as seen by the distant observer. For the radial and toroidal magnetic field topologies, the inner \quloop corresponds to the part of the orbit where the spot it is receding with respect to the observer. Based on our models we conclude that it is possible to constrain the underlying magnetic field topology with an analysis of the Q-U loop geometry, particularly in combination with a circular polarization measurements.

Submitted to A&A

References in corpus (24)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• 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
• First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon
• 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
• Black hole flares: ejection of accreted magnetic flux through 3D plasmoid-mediated reconnection
• X-ray hiccups from SgrA* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day
• Electron and proton heating in trans-relativistic magnetic reconnection
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Polarimetric properties of Event Horizon Telescope targets from ALMA
• Orbital motion near Sagittarius A* -- Constraints from polarimetric ALMA observations
• Magnetic Hair and Reconnection in Black Hole Magnetospheres
• The Polarized Image of a Synchrotron Emitting Ring of Gas Orbiting a Black Hole
• Polarized Image of Equatorial Emission in the Kerr Geometry
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• Dynamically important magnetic fields near the event horizon of Sgr A*
• Synthetic gamma-ray lightcurves of Kerr black-hole magnetospheric activity from particle-in-cell simulations
• The Effects of Accretion Flow Dynamics on the Black Hole Shadow of Sagittarius A${}^{\ast }$
• Decomposing the Internal Faraday Rotation of Black Hole Accretion Flows
• Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*
• Multi-wavelength torus-jet model for Sgr~A*

Cited by in corpus (17)

• Key Science Goals for the Next-Generation Event Horizon Telescope
• Imaging compact boson stars with hot-spots and thin accretion disks
• Polarimetry and Astrometry of NIR Flares as Event Horizon Scale, Dynamical Probes for the Mass of Sgr A*
• Reconnection-driven flares in 3D black hole magnetospheres -- A scenario for hot spots around Sagittarius A*
• The internal Faraday screen of Sagittarius A*
• Fitting the light curves of Sagittarius A* with a hot-spot model
• Rotation in Event Horizon Telescope Movies
• How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models
• Hot-spots around Sagittarius A*: Joint fits to astrometry and polarimetry
• Parameter study for hot spot trajectories around Sgr$A\ast$
• Magnetically arrested disk flux eruption events to describe SgrA* flares
• Forward Ray Tracing and Hot Spots in Kerr Spacetime
• Magnetic flux eruptions at the root of time-lags in low-luminosity AGN
• Prospects for ray-tracing light intensity and polarization in models of accreting compact objects using a GPU
• Semi-analytic studies of accretion disk and magnetic field geometry in M87*
• Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign
• Polarization Signatures of Inspiraling Hotspots around Kerr Black Holes