Flaring Activity of Sagittarius A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma

By F. Yusef-Zadeh, D. Roberts, M. Wardle, C. Heinke, G. Bower. 2006

132 citations recorded by the source corpus.

We have carried out Very Large Array (VLA) continuum observations to study the variability of Sgr A* at 43 GHz (λ = 7 mm) and 22 GHz (λ = 13 mm). A low level of flare activity has been detected with a duration of ~2 hr at these frequencies, showing the peak flare emission at 43 GHz leading the 22 GHz peak flare by ~20-40 minutes. The overall characteristics of the flare emission are interpreted in terms of the plasmon model of van der Laan by considering the ejection and adiabatic expansion of a uniform, spherical plasma blob due to flare activity. The observed peak of the flare emission with a spectral index, ν-α, of α = 1.6 is consistent with the prediction that the peak emission shifts toward lower frequencies in an adiabatically expanding self-absorbed source. We present the expected synchrotron light curves for an expanding blob, as well as the peak frequency emission, as a function of the energy spectral index constrained by the available flaring measurements in near-IR, submillimeter, millimeter, and radio wavelengths. We note that the blob model is consistent with the available measurements; however, we cannot rule out the jet of Sgr A*. If expanding material leaves the gravitational potential of Sgr A*, the total mass-loss rate of nonthermal and thermal particles is estimated to be ≤2 × 10-8 M☉ yr-1. We discuss the implication of the mass-loss rate, since this value matches closely the estimated accretion rate based on polarization measurements.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/ad1f3f4db65c17de44cb6046385ffcd653d279e2

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In Astronomy and Astrophysics

1. T. Johannsen
2. Ramesh Narayan
3. F. Yuan
4. Cosimo Bambi
5. Abraham Loeb
6. W. N. Brandt
7. A. Broderick
8. A. Ghez

In Geophysics

1. Ramesh Narayan
2. F. Yuan
3. Cosimo Bambi
4. Abraham Loeb

Citations in the corpus

• Testing black hole candidates with electromagnetic radiation (2015, background): “These flares may be associated with blobs of plasma orbiting near the ISCO of the supermassive BH candidate (Hamaus et al., 2009), even if current observations cannot exclude other explanations (Markoff et al., 2001; Tagger & Melia, 2006; Yusef-Zadeh et al., 2006).”
• Hot Accretion Flows Around Black Holes (2014, background): “However, there is a hint that these jets can occur also at lower luminosities (Cyg X-1, Fender et al. 2006; Sgr A*, Yusef-Zadeh et al. 2006, §4.1.3; other examples are reviewed in Yuan et al. 2009a).”
• An X-Ray, Infrared, and Submillimeter Flare of Sagittarius A* (2007, methodology): “An exception is the expanding plasmon model used by Yusef-Zadeh et al. (2006a) to explain delays between flares observed in two centimeter wavelength bands; the extension of this model to shorter wavelengths is discussed in this paper.”
• DETECTING FLARING STRUCTURES IN SAGITTARIUS A* WITH HIGH-FREQUENCY VLBI (2008, background): “…and X-ray bands (e.g., Baganoff et al. 2001; Aschenbach et al. 2004; Genzel et al. 2003; Ghez et al. 2004; Bélanger et al. 2006; Meyer et al. 2006; Yusef-Zadeh et al. 2006; Marrone et al. 2006; Hornstein et al. 2007), and flare rise times in the X-ray and NIR correspond to light-crossing times…”