The flux distribution of Sgr A*
Journal
Date Issued
2020
Author(s)
GRAVITY Collaboration
•
Abuter, R.
•
Amorim, A.
•
Bauböck, M.
•
Berger, J. B.
•
Bonnet, H.
•
Brandner, W.
•
Cardoso, V.
•
Clénet, Y.
•
de Zeeuw, P. T.
•
Dallilar, Y.
•
Dexter, J.
•
Eckart, A.
•
Eisenhauer, F.
•
Förster Schreiber, N. M.
•
Garcia, P.
•
Gao, F.
•
Gendron, E.
•
Genzel, R.
•
Gillessen, S.
•
Habibi, M.
•
Haubois, X.
•
Henning, T.
•
Hippler, S.
•
Horrobin, M.
•
Jiménez-Rosales, A.
•
Jochum, L.
•
Jocou, L.
•
Kaufer, A.
•
Kervella, P.
•
Lacour, S.
•
Lapeyrère, V.
•
Le Bouquin, J. -B.
•
Léna, P.
•
Nowak, M.
•
Ott, T.
•
Paumard, T.
•
Perraut, K.
•
Perrin, G.
•
Pfuhl, O.
•
•
Rodriguez Coira, G.
•
Shangguan, J.
•
Scheithauer, S.
•
Stadler, J.
•
Straub, O.
•
Straubmeier, C.
•
Sturm, E.
•
Tacconi, L. J.
•
Vincent, F.
•
von Fellenberg, S. D.
•
Waisberg, I.
•
Widmann, F.
•
Wieprecht, E.
•
Wiezorrek, E.
•
Woillez, J.
•
Yazici, S.
•
Zins, G.
Abstract
The Galactic center black hole Sagittarius A* is a variable near-infrared (NIR) source that exhibits bright flux excursions called flares. When flux from Sgr A* is detected, the light curve has been shown to exhibit red noise characteristics and the distribution of flux densities is non-linear, non-Gaussian, and skewed to higher flux densities. However, the low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. For this reason, the median NIR flux has only been inferred indirectly from model fitting, but it has not been directly measured. In order to explore the lowest flux ranges, to measure the median flux density, and to test if the previously proposed flux distributions fit the data, we use the unprecedented resolution of the GRAVITY instrument at the VLTI. We obtain light curves using interferometric model fitting and coherent flux measurements. 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 Sgr A* turns over at a median flux density of (1.1 ± 0.3) mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band spectral energy distribution. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1 mJy 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.
Volume
638
Start page
A2
Issn Identifier
0004-6361
Ads BibCode
2020A&A...638A...2G
Rights
open.access
File(s)![Thumbnail Image]()
![Thumbnail Image]()
Loading...
Name
GravityB.pdf
Size
957.2 KB
Format
Adobe PDF
Checksum (MD5)
91fc1d966b6e8346da74b72d74eb1880
Loading...
Name
aa37717-20.pdf
Description
pdf editoriale
Size
929.66 KB
Format
Adobe PDF
Checksum (MD5)
423129ba5f41bcffa96550e4976a61d5