Modeling mm- to X-ray flare emission from sagittarius A

A. Eckart, F. K. Baganoff, M. R. Morris, D. Kunneriath, M. Zamaninasab, G. Witzel, R. Schödel, M. García-Marín, L. Meyer, G. C. Bower, D. Marrone, M. W. Bautz, W. N. Brandt, G. P. Garmire, G. R. Ricker, C. Straubmeier, D. A. Roberts, K. Muzic, J. Mauerhan, A. Zensus

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


Context. We report on new modeling results based on the mm- to X-ray emission of the SgrA* counterpart associated with the massive ∼4×106 Mȯ black hole at the Galactic Center.Aims. We investigate the physical processes responsible for the variable emission from SgrA*. Methods. Our modeling is based on simultaneous observations carried out on 07 July, 2004, using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope*and the ACIS-I instrument aboard the Chandra X-ray Observatory as well as the Submillimeter Array SMA**on Mauna Kea, Hawaii, and the Very Large Array***in New Mexico. Results. The observations revealed several flare events in all wavelength domains. Here we show that the flare emission can be described with a combination of a synchrotron self-Compton (SSC) model followed by an adiabatic expansion of the source components. The SSC emission at NIR and X-ray wavelengths involves up-scattered sub-millimeter photons from a compact source component. At the start of the flare, spectra of these components peak at frequencies between several 100 GHz and 2 THz. The adiabatic expansion then accounts for the variable emission observed at sub-mm/mm wavelengths. The derived physical quantities that describe the flare emission give a blob expansion speed of vexp ∼ 0.005 c, magnetic field of B around 60 G or less and spectral indices of α = 0.8 to 1.4, corresponding to a particle spectral index p ∼2.6 to 3.8. Conclusions. A combined SSC and adiabatic expansion model can fully account for the observed flare flux densities and delay times covering the spectral range from the X-ray to the mm-radio domain. The derived model parameters suggest that the adiabatic expansion takes place in source components that have a bulk motion larger than vexp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*.

Original languageEnglish (US)
Pages (from-to)935-946
Number of pages12
JournalAstronomy and astrophysics
Issue number3
StatePublished - Jun 2009


  • Accretion, accretion disks
  • Black hole physics
  • Galaxy: center
  • Galaxy: nucleus
  • Infrared: general
  • X-rays: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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