The two states of Sgr A* in the near-infrared: Bright episodic flares on top of low-level continuous variability

K. Dodds-Eden*, S. Gillessen, T. K. Fritz, F. Eisenhauer, S. Trippe, R. Genzel, T. Ott, H. Bartko, O. Pfuhl, G. Bower, A. Goldwurm, D. Porquet, G. Trap, F. Yusef-Zadeh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


In this paper, we examine properties of the variable source Sgr A * in the near-infrared (NIR) using a very extensive Ks-band data set from NACO/VLT observations taken in 2004-2009. We investigate the variability of Sgr A* with two different photometric methods and analyze its flux distribution. We find that Sgr A* is continuously emitting and continuously variable in the near-infrared, with some variability occurring on timescales as long as weeks. The flux distribution can be described by a lognormal distribution at low intrinsic fluxes (≲5mJy, dereddened with AKs = 2.5). The lognormal distribution has a median flux of ≈1.1 mJy, but above 5mJy the flux distribution is significantly flatter (high flux events are more common) than expected for the extrapolation of the lognormal distribution to high fluxes. We make a general identification of the low-level emission above 5mJy as flaring emission and of the low-level emission as the quiescent state. We also report here the brightest Ks-band flare ever observed (from 2008 August 5) which reached an intrinsic Ks-band flux of 27.5mJy (mKs = 13.5). This flare was a factor 27 increase over the median flux of Sgr A*, close to double the brightness of the star S2, and 40% brighter than the next brightest flare ever observed from Sgr A *.

Original languageEnglish (US)
JournalAstrophysical Journal
Issue number1
StatePublished - Feb 10 2011


  • Accretion, accretion disks
  • Black hole physics
  • Galaxy: center
  • Infrared: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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