General relativistic effects and the near-infrared and X-ray variability of Sgr A* I

Fellenberg, S. D. von; Witzel, G.; Bauböck, M.; Chung, Hui-Hsuan; Aimar, N.; Bordoni, M. Sadun; Drescher, A.; Eisenhauer, F.; Genzel, R.; Gillessen, S.; Marchili, N.; Paumard, T.; Perrin, G.; Ott, Thomas; Ribeiro, D. C.; Ros, E.; Vincent, F.; Widmann, F.; Willner, S. P.; Zensus, J. A.

doi:10.1051/0004-6361/202245575

Cited by 7 publications

(2 citation statements)

References 85 publications

(107 reference statements)

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“…An early extensive review on this object can be found for general properties in Genzel et al (2010). It has been extensively observed through multiwavelength campaigns during the last 20 years and shows a diversity of variability properties (see a brief summary of observations in Witzel et al 2021;Boyce et al 2022;von Fellenberg et al 2023). The powerful astrometric measurements of GRAVITY/VLTI provide an exciting ring of locations of flares during the last four years.…”

Section: Application To Sgr a *mentioning

confidence: 99%

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Slowly Transient Appearance

Wang

Liu

et al. 2021

ApJL

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Compact objects are expected to exist in the accretion disks of supermassive black holes (SMBHs) in active galactic nuclei (AGNs), and in the presence of such a dense environment (∼1014 cm−3), they will form a new kind of stellar population denoted as accretion-modified stars (AMSs). This hypothesis is supported by recent LIGO/Virgo detection of the mergers of very high-mass stellar binary black holes (BHs). We show that the AMSs will be trapped by the SMBH disk within a typical AGN lifetime. In the context of SMBH disks, the rates of Bondi accretion onto BHs are ∼109 L Edd/c 2, where L Edd is the Eddington luminosity and c is the speed of light. Outflows developed from the hyper-Eddington accretion strongly impact the Bondi sphere and induce episodic accretion. We show that the hyper-Eddington accretion will be halted after an accretion interval of t a ∼ 105 m 1 s, where m 1 = m •/10M ⊙ is the BH mass. The kinetic energy of the outflows accumulated during t a is equivalent to 10 supernovae driving an explosion of the Bondi sphere and developing blast waves. We demonstrate that a synchrotron flare from relativistic electrons accelerated by the blast waves peaks in the soft X-ray band (∼0.1 keV), significantly contributing to the radio, optical, UV, and soft X-ray emission of typical radio-quiet quasars. External inverse Compton scattering of the electrons peaks around 40 GeV and is detectable through Fermi-LAT. The flare, decaying with t −6/5 with a few months, will appear as a slowly varying transient. The flares, occurring at a rate of a few per year in radio-quiet quasars, provide a new mechanism for explaining AGN variability.

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Section: Application To Sgr a *mentioning

confidence: 99%

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Slowly Transient Appearance

Wang

Liu

et al. 2021

ApJL

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“…An early extensive review on this object can be found for general properties in Genzel et al (2010). It has been extensively observed through multiwavelength campaigns during the last 20 yr and shows a diversity of variability properties (see a brief summary of observations in Witzel et al 2021;Boyce et al 2022;von Fellenberg et al 2023). The powerful astrometric measurements of GRAVITY/VLTI provide an exciting ring of locations of flares during the last 4 yr.…”

Section: Parameters Meaningsmentioning

confidence: 99%

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: The Low-luminosity Cases and an Application to Sgr A*

Wang,

Liu,

et al. 2023

ApJL

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In this paper, we investigate the astrophysical processes of stellar-mass black holes (sMBHs) embedded in advection-dominated accretion flows (ADAFs) of supermassive black holes (SMBHs) in low-luminosity active galactic nuclei. The sMBH is undergoing Bondi accretion at a rate lower than the SMBH. Outflows from the sMBH-ADAF dynamically interact with their surroundings and form a cavity inside the SMBH-ADAF, thereby quenching the accretion onto the sMBH. Rejuvenation of the Bondi accretion is rapidly done by turbulence. These processes give rise to quasi-periodic episodes of sMBH activities and create flickerings from relativistic jets developed by the Blandford–Znajek mechanism if the sMBH is maximally rotating. Accumulating successive sMBH-outflows trigger a viscous instability of the SMBH-ADAF, leading to a flare following a series of flickerings. Recently, the similarity of near-infrared flare’s orbits has been found by GRAVITY/VLTI astrometric observations of Sgr A∗: their loci during the last 4 yr consist of a ring in agreement with the well-determined SMBH mass. We apply the present model to Sgr A*, which shows quasi-periodic flickerings. An sMBH of ∼40M ⊙ is preferred orbiting around the central SMBH of Sgr A* from fitting radio to X-ray continuum. Such an extreme mass ratio inspiraling provides an excellent laboratory for LISA/Taiji/Tianqin detection of mHz gravitational waves with strains of ∼10−17, as well as their polarization.

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Polarimetry and astrometry of NIR flares as event horizon scale, dynamical probes for the mass of Sgr A*

Abuter,

Aimar,

Amaro Seoane

et al. 2023

A&A

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We present new astrometric and polarimetric observations of flares from Sgr A* obtained with GRAVITY, the near-infrared interferometer at ESO’s Very Large Telescope Interferometer (VLTI), bringing the total sample of well-covered astrometric flares to four and polarimetric flares to six. Of all flares, two are well covered in both domains. All astrometric flares show clockwise motion in the plane of the sky with a period of around an hour, and the polarization vector rotates by one full loop in the same time. Given the apparent similarities of the flares, we present a common fit, taking into account the absence of strong Doppler boosting peaks in the light curves and the EHT-measured geometry. Our results are consistent with and significantly strengthen our model from 2018. First, we find that the combination of polarization period and measured flare radius of around nine gravitational radii (9Rg ≈ 1.5RISCO, innermost stable circular orbit) is consistent with Keplerian orbital motion of hot spots in the innermost accretion zone. The mass inside the flares’ radius is consistent with the 4.297 × 106 M⊙ measured from stellar orbits at several thousand Rg. This finding and the diameter of the millimeter shadow of Sgr A* thus support a single black hole model. Second, the magnetic field configuration is predominantly poloidal (vertical), and the flares’ orbital plane has a moderate inclination with respect to the plane of the sky, as shown by the non-detection of Doppler-boosting and the fact that we observe one polarization loop per astrometric loop. Finally, both the position angle on the sky and the required magnetic field strength suggest that the accretion flow is fueled and controlled by the winds of the massive young stars of the clockwise stellar disk 1–5″ from Sgr A*, in agreement with recent simulations.

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General relativistic effects and the near-infrared and X-ray variability of Sgr A* I

Cited by 7 publications

References 85 publications

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Slowly Transient Appearance

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Slowly Transient Appearance

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: The Low-luminosity Cases and an Application to Sgr A*

Polarimetry and astrometry of NIR flares as event horizon scale, dynamical probes for the mass of Sgr A*

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