The Flux Distribution of Sgr A*

Abstract

The Galactic Center black hole Sagittarius A* is a variable NIR source that exhibits bright flux excursions called flares. The low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. We use the unprecedented resolution of the GRAVITY instrument at the VLTI. Our light curves are unconfused, overcoming the confusion limit of previous photometric studies. We analyze the light curves using standard statistical methods and obtain the flux distribution. We find that the flux distribution of SgrA* turns over at a median flux density of (1.1\pm0.3)mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band SED. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1mJy are hardly ever observed. In consequence, a single powerlaw or lognormal distribution does not suffice to describe the observed flux distribution in its entirety. However, if one takes into account a power law component at high flux densities, a lognormal distribution can describe the lower end of the observed flux distribution. We confirm the RMS-flux relation for Sgr~A* and find it to be linear for all flux densities in our observation. We conclude that Sgr~A* has two states: the bulk of the emission is generated in a lognormal process with a well-defined median flux density and this quiescent emission is supplemented by sporadic flares that create the observed power law extension of the flux distribution.

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Cited by in corpus (42)

• 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 Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• 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
• Fast-moving stars around an intermediate-mass black hole in Omega Centauri
• Polarimetry and Astrometry of NIR Flares as Event Horizon Scale, Dynamical Probes for the Mass of Sgr A*
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• Dynamically important magnetic fields near the event horizon of Sgr A*
• Sgr A* X-ray flares from non-thermal particle acceleration in a magnetically arrested disc
• General relativistic MHD simulations of non-thermal flaring in Sagittarius A*
• Gravitational lensing of a Schwarzschild-like black hole in Kalb-Ramond gravity
• The light ring and the appearance of matter accreted by black holes
• Magnetic reconnection plasmoid model for Sagittarius A* flares
• Detection of faint stars near SgrA* with GRAVITY
• Deep Images of the Galactic Center with GRAVITY
• The Galactic Center as a laboratory for theories of gravity and dark matter
• Probing spacetime and accretion model for the Galactic Center: Comparison of Kerr and dilaton black hole shadows
• Second Scale Submillimeter Variability of Sagittarius A* during flaring activity of 2019: On the Origin of Bright Near Infrared Flares
• Two-Temperature GRMHD Simulations of Black Hole Accretion Flows with Multiple Magnetic Loops
• Radio jet precession in M81*
• Multi-wavelength Variability of Sagittarius A* in July 2019
• The Relationship Between Simulated Sub-Millimeter and Near-Infrared Images of Sagittarius A* from a Magnetically Arrested Black Hole Accretion Flow
• Observational Appearance of a Freely-falling Star in an Asymmetric Thin-shell Wormhole
• Hot-spots around Sagittarius A*: Joint fits to astrometry and polarimetry
• Probing Plasma Physics with Spectral Index Maps of Accreting Black Holes on Event Horizon Scales
• Dynamics and Emission Properties of Flux Ropes from Two-Temperature GRMHD Simulations with Multiple Magnetic Loops
• Constraints on metric-affine gravity black holes from the stellar motion at the Galactic Center
• High-energy Gamma-rays from Magnetically Arrested Disks in Nearby Radio Galaxies
• Magnetic flux eruptions at the root of time-lags in low-luminosity AGN
• General Relativistic effects and the NIR variability of Sgr A* II: A systematic approach to temporal asymmetry
• S0-2 star, G1- and G2-objects and flaring activity of the Milky Way's Galactic Center black hole in 2019
• New Evidence for a Flux-independent Spectral Index of Sgr A* in the Near-infrared
• Doppler Boosting of the S-stars in the Galactic Center
• Mid-infrared extinction toward the Galactic center
• Non-thermal Synchrotron Emission and Polarization Signatures during Black Hole Flux Eruptions
• Auto- and cross-correlations for multiple images of corotating hotspots in accretion disks
• Search for long-term variability of HESS J1745-290
• High Energy Emission from the Galactic Center
• Radiative energy from a reconnection region around massive black hole
• Remarkable correspondence of Sagittarius A* submillimeter variability with a stellar-wind-fed accretion flow model
• Sagittarius A* near-infrared flares polarization as a probe of space-time I: Non-rotating exotic compact objects