Imaging optically-thin hotspots near the black hole horizon of Sgr A* at radio and near-infrared wavelengths

By A. Broderick, Abraham Loeb Institute for Theory, Computation, Harvard University. 2005

205 citations recorded by the source corpus.

Submilliarcsecond astrometry and imaging of the black hole Sgr A* at the Galactic Centre may become possible in the near future at infrared and submillimetre wavelengths. Motivated by the observations of short-term infrared and X-ray variability of Sgr A*, in a previous paper, we computed the expected images and light curves, including polarization, associated with a compact emission region orbiting the central black hole. We extend this work, using a more realistic hotspot model and including the effects of opacity in the underlying accretion flow. We find that at infrared wavelengths, the qualitative features identified by our earlier work are present, namely it is possible to extract the black hole mass and spin from spot images and light curves of the observed flux and polarization. At radio wavelengths, disc opacity produces significant departures from the infrared behaviour, but there are still generic signatures of the black hole properties. Detailed comparison of these results with future data can be used to test general relativity and to improve existing models for the accretion flow in the immediate vicinity of the black hole.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/78fa9acb8023b3043fe22f82814e272d51bfbfd1

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Citations in the corpus

TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. II. BLACK HOLE IMAGES (2010, background): “…within general relativity that are suitable to these observations have been reported by a number of authors (Bardeen 1973; Speith et al. 1995; Fanton et al. 1997; Falcke et al. 2000; Takahashi 2004; Beckwith & Done 2004, 2005; Dexter & Agol 2009; Broderick & Loeb 2005, 2006; Yuan et al. 2009).”
Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA* (2018, methodology): “At such low inclinations, almost face on, one would also expect little lensing and multiple images for R ≥ 6 Rg (see Broderick & Loeb 2006; Hamaus et al. 2009), again consistent with our observations.”
EVIDENCE FOR LOW BLACK HOLE SPIN AND PHYSICALLY MOTIVATED ACCRETION MODELS FROM MILLIMETER-VLBI OBSERVATIONS OF SAGITTARIUS A* (2010, methodology): “(1) Here we describe three classes of model images: those associated with radiatively inefficient accretion flows (RIAFs)of the form discussed in Broderick & Loeb (2006a), symmetric and asymmetric gaussians.”
DETECTING FLARING STRUCTURES IN SAGITTARIUS A* WITH HIGH-FREQUENCY VLBI (2008, methodology): “The method by which images of the flaring disk are produced is discussed at length in Broderick & Blandford (2003; see also Broderick & Loeb 2006a, 2006b).”
Polarimetry of near-infrared flares from Sagittarius A* (2006, background): “Here we have assumed that the spot has an intrinsic linear polarization of 60% (Broderick & Loeb 2006; Falcke et al. 2000; Goldston et al. 2005).”
An X-Ray, Infrared, and Submillimeter Flare of Sagittarius A* (2007, background): “Observations of repeated structures in IR and X-ray flares (e.g. Eckart et al. 2006a; Meyer et al. 2006b; Bélanger et al. 2006) have often been attributed to plasma “hot spots” orbiting the black hole (e.g. Broderick & Loeb 2006; Marrone et al. 2006b; Meyer et al. 2006a; Trippe et al. 2007).”
Flaring Activity of Sagittarius A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma (2006, methodology): “Given that the orbiting hot spot model predicts no time delay in flare emission (see Figure 11 of Broderick and Loeb 2006), we briefly view the expanding blob in the context of a jet model.”
PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES (2013, methodology): “…observations of Sgr A* with measurements of its spectral energy distribution (Yuan et al. 2004 and references therein; Marrone 2006) and obtained values of the spin magnitude and direction employing a radiatively inefficient accretion flow (RIAF) model (Yuan et al. 2003; Broderick & Loeb 2006a).”
THE EVENT HORIZON OF SAGITTARIUS A* (2009, background): “However, this is easily rectified if the emission region is interpreted instead as the visible arc of an oncoming accretion disk (as a result of Doppler boosting and Doppler shifts, the receding side being considerably dimmer for the same reason; Broderick & Loeb 2006a).”
RADIATIVE MODELS OF SGR A* FROM GRMHD SIMULATIONS (2009, background): “Other workers have modeled the VLBI and submillimeter emission (Broderick & Loeb 2005, 2006a, 2006b; Huang et al. 2007; Miyoshi et al. 2008; Broderick et al. 2009; Yuan et al. 2009) assuming a stationary RIAF or time-dependent general relativis- tic MHD models (Dexter et al. 2009) and computing…”