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Astrophysical Journal 728 (2011) 37
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. Goldwurm1, 2, D. Porquet3, G. Trap1, 2, F. Yusef-Zadeh
(02/2011)

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*.
1 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
2 :  APC - UMR 7164 - AstroParticule et Cosmologie
3 :  OAS - Observatoire astronomique de Strasbourg
APC - AHE
Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie

Physique/Astrophysique/Phénomènes cosmiques de haute energie
accretion – accretion disks – black hole physics – Galaxy: center – infrared: general
Lien vers le texte intégral : 
http://fr.arXiv.org/abs/1008.1984