Abuter, R., Amorim, A., Bauboeck, M., Berger, J. B., Bonnet, H., Brandner, W., Cardoso, V, Clenet, Y., de Zeeuw, P. T., Dallilar, Y., Dexter, J., Eckart, A., Eisenhauer, F., Schreiber, N. M. Foerster, Garcia, P., Gao, F., Gendron, E., Genzel, R., Gillessen, S., Habibi, M., Haubois, X., Henning, T., Hippler, S., Horrobin, M., Jimenez-Rosales, A., Jochum, L., Jocou, L., Kaufer, A., Kervella, P., Lacour, S., Lapeyrere, V, Le Bouquin, J-B, Lena, P., Nowak, M., Ott, T., Paumard, T., Perraut, K., Perrin, G., Pfuhl, O., Ponti, G., Coira, G. Rodriguez, 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. and Zins, G. (2020). The flux distribution of Sgr A*. Astron. Astrophys., 638. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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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.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Abuter, R.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Amorim, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Bauboeck, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Berger, J. B.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Bonnet, H.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Brandner, W.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Cardoso, VUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Clenet, Y.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
de Zeeuw, P. T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Dallilar, Y.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Dexter, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Eckart, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Eisenhauer, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Schreiber, N. M. FoersterUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Garcia, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Gao, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Gendron, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Genzel, R.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Gillessen, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Habibi, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Haubois, X.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Henning, T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Hippler, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Horrobin, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Jimenez-Rosales, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Jochum, L.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Jocou, L.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Kaufer, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Kervella, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Lacour, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Lapeyrere, VUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Le Bouquin, J-BUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Lena, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Nowak, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ott, T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Paumard, T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Perraut, K.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Perrin, G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Pfuhl, O.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ponti, G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Coira, G. RodriguezUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Shangguan, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Scheithauer, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Stadler, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Straub, O.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Straubmeier, C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Sturm, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Tacconi, L. J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Vincent, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
von Fellenberg, S. D.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Waisberg, IUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Widmann, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wieprecht, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wiezorrek, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Woillez, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Yazici, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Zins, G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-332614
DOI: 10.1051/0004-6361/202037717
Journal or Publication Title: Astron. Astrophys.
Volume: 638
Date: 2020
Publisher: EDP SCIENCES S A
Place of Publication: LES ULIS CEDEX A
ISSN: 1432-0746
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
NEAR-INFRARED FLARES; LIGHT CURVES; MODELS; VARIABILITY; EMISSIONMultiple languages
Astronomy & AstrophysicsMultiple languages
URI: http://kups.ub.uni-koeln.de/id/eprint/33261

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