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  The flux distribution of Sgr A*

Abuter, R., Amorim, A., Bauböck, M., Berger, J. B., Bonnet, H., Brandner, W., et al. (2020). The flux distribution of Sgr A*. Astronomy and Astrophysics, 638: A2. doi:10.1051/0004-6361/202037717.

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Abuter, R., Author
Amorim, A., Author
Bauböck, M.1, Author           
Berger, J. B., Author
Bonnet, H., Author
Brandner, W., Author
Cardoso, V., Author
Clénet, Y., Author
de Zeeuw, P. T.1, Author           
Dallilar, Y.1, Author           
Dexter, J.1, Author           
Eckart, A., Author
Eisenhauer, F.1, Author           
Förster Schreiber, N. M.1, Author           
Garcia, P., Author
Gao, F.1, Author           
Gendron, E., Author
Genzel, R.1, Author           
Gillessen, S.1, Author           
Habibi, M.1, Author           
Haubois, X., AuthorHenning, T., AuthorHippler, S., AuthorHorrobin, M., AuthorJiménez-Rosales, A.1, Author           Jochum, L., AuthorJocou, L., AuthorKaufer, A., AuthorKervella, P., AuthorLacour, S., AuthorLapeyrère, V., AuthorLe Bouquin, J.-B., AuthorLéna, P., AuthorNowak, M., AuthorOtt, T.1, Author           Paumard, T., AuthorPerraut, K., AuthorPerrin, G., AuthorPfuhl, O.1, Author           Ponti, G.2, Author           Coira, G. Rodriguez, AuthorShangguan, J.1, Author           Scheithauer, S., AuthorStadler, J.1, Author           Straub, O.1, Author           Straubmeier, C., AuthorSturm, E.1, Author           Tacconi, L. J.1, Author           Vincent, F., AuthorFellenberg, S. D. von1, Author           Waisberg, I., AuthorWidmann, F.1, Author           Wieprecht, E.1, Author           Wiezorrek, E.1, Author           Woillez, J., AuthorYazici, S.1, Author           Zins, G., Author more..
1Infrared and Submillimeter Astronomy, MPI for Extraterrestrial Physics, Max Planck Society, ou_159889              
2High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society, ou_159890              


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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.


 Dates: 2020-05-29
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1051/0004-6361/202037717
Other: LOCALID: 3250531
 Degree: -



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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
Publ. Info: France : EDP Sciences S A
Pages: - Volume / Issue: 638 Sequence Number: A2 Start / End Page: - Identifier: ISSN: 1432-0746
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1