TY - JOUR
AU - R. Abuter
AU - A. Amorim
AU - M. Bauboeck
AU - H. Bonnet
AU - W. Brandner
AU - V. Cardoso
AU - Y. Clenet
AU - P. de Zeeuw
AU - Jason Dexter
AU - A. Eckart
AU - Frank Eisenhauer
AU - N. Schreiber
AU - P. Garcia
AU - F. Gao
AU - E. Gendron
AU - R. Genzel
AU - S. Gillessen
AU - M. Habibi
AU - X. Haubois
AU - T. Henning
AU - S. Hippler
AU - M. Horrobin
AU - L. Jocou
AU - Alejandra Jimenez-Rosales
AU - L. Jochum
AU - L. Jocou
AU - A. Kaufer
AU - P. Kervella
AU - S. Lacour
AU - V. Lapeyrère
AU - J. Le Bouquin
AU - P. Léna
AU - M. Nowak
AU - T. Ott
AU - T. Paumard
AU - K. Perraut
AU - G. Perrin
AU - Oliver Pfuhl
AU - G. Ponti
AU - Rodriguez Coira
AU - J. Shangguan
AU - S. Scheithauer
AU - J. Stadler
AU - O. Straub
AU - C. Straubmeier
AU - E. Sturm
AU - L. Tacconi
AU - K. Tristram
AU - F. Vincent
AU - S. von Fellenberg
AU - I. Waisberg
AU - F. Widmann
AU - E. Wieprecht
AU - E. Wiezorrek
AU - J. Woillez
AU - S. Yazici
AU - G. Zins
AB - The Galactic Center black hole Sagittarius A* is a variable NIR source that exhibits bright flux excursions called flares. The low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. We use the unprecedented resolution of the GRAVITY instrument at the VLTI. Our light curves are unconfused, overcoming the confusion limit of previous photometric studies. We analyze the light curves using standard statistical methods and obtain the flux distribution. We find that the flux distribution of SgrA* turns over at a median flux density of (1.1\pm0.3)mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band SED. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1mJy are hardly ever observed. In consequence, a single powerlaw or lognormal distribution does not suffice to describe the observed flux distribution in its entirety. However, if one takes into account a power law component at high flux densities, a lognormal distribution can describe the lower end of the observed flux distribution. We confirm the RMS-flux relation for Sgr~A* and find it to be linear for all flux densities in our observation. We conclude that Sgr~A* has two states: the bulk of the emission is generated in a lognormal process with a well-defined median flux density and this quiescent emission is supplemented by sporadic flares that create the observed power law extension of the flux distribution.
BT - Astronomy & Astrophysics
DA - 2020-06
DO - 10.1051/0004-6361/202037717
N2 - The Galactic Center black hole Sagittarius A* is a variable NIR source that exhibits bright flux excursions called flares. The low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. We use the unprecedented resolution of the GRAVITY instrument at the VLTI. Our light curves are unconfused, overcoming the confusion limit of previous photometric studies. We analyze the light curves using standard statistical methods and obtain the flux distribution. We find that the flux distribution of SgrA* turns over at a median flux density of (1.1\pm0.3)mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band SED. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1mJy are hardly ever observed. In consequence, a single powerlaw or lognormal distribution does not suffice to describe the observed flux distribution in its entirety. However, if one takes into account a power law component at high flux densities, a lognormal distribution can describe the lower end of the observed flux distribution. We confirm the RMS-flux relation for Sgr~A* and find it to be linear for all flux densities in our observation. We conclude that Sgr~A* has two states: the bulk of the emission is generated in a lognormal process with a well-defined median flux density and this quiescent emission is supplemented by sporadic flares that create the observed power law extension of the flux distribution.
PY - 2020
EP - A2
T2 - Astronomy & Astrophysics
TI - The Flux Distribution of Sgr A*
UR - https://www.aanda.org/articles/aa/full_html/2020/06/aa37717-20/aa37717-20.html
VL - 638
ER -