The Two States of Sgr A* in the Near-infrared: Bright Episodic Flares on Top of Low-level Continuous Variability

Abstract : 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 (lsim5 mJy, dereddened with AKs = 2.5). The lognormal distribution has a median flux of ≈1.1 mJy, but above 5 mJy 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 5 mJy 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 27.5 mJy (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*.
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Journal articles
Astrophysical Journal, American Astronomical Society, 2011, 728, pp.37. <10.1088/0004-637X/728/1/37>


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Submitted on : Thursday, September 27, 2012 - 5:07:50 PM
Last modification on : Thursday, April 23, 2015 - 2:17:34 PM

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K. Dodds-Eden, S. Gillessen, T. K. Fritz, F. Eisenhauer, S. Trippe, et al.. The Two States of Sgr A* in the Near-infrared: Bright Episodic Flares on Top of Low-level Continuous Variability. Astrophysical Journal, American Astronomical Society, 2011, 728, pp.37. <10.1088/0004-637X/728/1/37>. <hal-00736188>

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