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  Constraining particle acceleration in Sgr A(*) with simultaneous GRAVITY, Spitzer, NuSTAR, and Chandra observations

Abuter, R., Amorim, A., Bauböck, M., Bagano, F., Berger, J. P., Boyce, H., et al. (2021). Constraining particle acceleration in Sgr A(*) with simultaneous GRAVITY, Spitzer, NuSTAR, and Chandra observations. Astronomy and Astrophysics, 654: A22. doi:10.1051/0004-6361/202140981.

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Abuter, R., Author
Amorim, A., Author
Bauböck, M.1, Author              
Bagano, F., Author
Berger, J. P., Author
Boyce, H., Author
Bonnet, H., Author
Brandner, W., Author
Clénet, Y., Author
Davies, R.1, Author              
de Zeeuw, P. T.1, Author              
Dexter, J.1, Author              
Dallilar, Y.1, Author              
Drescher, A., Author
Eckart, A., Author
Eisenhauer, F.1, Author              
Fazio, G. G., Author
Förster Schreiber, N. M.1, Author              
Foster, K., Author
Gammie, C., Author
Garcia, P., AuthorGao, F.1, Author              Gendron, E., AuthorGenzel, R.1, Author              Ghisellini, G., AuthorGillessen, S.1, Author              Gurwell, M. A., AuthorHabibi, M.1, Author              Haggard, D., AuthorHailey, C., AuthorHarrison, F. A., AuthorHaubois, X., AuthorHeißel, G., AuthorHenning, T., AuthorHippler, S., AuthorHora, J. L., 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., AuthorLowrance, P. J., AuthorLutz, D.1, Author              Marko, S., AuthorMori, K., AuthorMorris, M. R., AuthorNeilsen, J., AuthorNowak, M., AuthorOtt, T.1, Author              Paumard, T., AuthorPerraut, K., AuthorPerrin, G., AuthorPonti, G.2, Author              Pfuhl, O.1, Author              Rabien, S.1, Author              Rodríguez-Coira, G., AuthorShangguan, J.1, Author              Shimizu, T.1, Author              Scheithauer, S., AuthorSmith, H. A., AuthorStadler, J.1, Author              Stern, D. K., AuthorStraub, 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              Willner, S. P., AuthorWitzel, G., AuthorWoillez, J., AuthorYazici, S.1, Author              Young, A., AuthorZhang, S., AuthorZins, G., Author more..
Affiliations:
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: We report the time-resolved spectral analysis of a bright near-infrared and moderate X-ray flare of Sgr A. We obtained light curves in the M, K, and H bands in the mid- and near-infrared and in the 2 − 8 keV and 2 − 70 keV bands in the X-ray. The observed spectral slope in the near-infrared band is νLν ∝  ν0.5 ± 0.2; the spectral slope observed in the X-ray band is νLν ∝ ν−0.7 ± 0.5. Using a fast numerical implementation of a synchrotron sphere with a constant radius, magnetic field, and electron density (i.e., a one-zone model), we tested various synchrotron and synchrotron self-Compton scenarios. The observed near-infrared brightness and X-ray faintness, together with the observed spectral slopes, pose challenges for all models explored. We rule out a scenario in which the near-infrared emission is synchrotron emission and the X-ray emission is synchrotron self-Compton. Two realizations of the one-zone model can explain the observed flare and its temporal correlation: one-zone model in which the near-infrared and X-ray luminosity are produced by synchrotron self-Compton and a model in which the luminosity stems from a cooled synchrotron spectrum. Both models can describe the mean spectral energy distribution (SED) and temporal evolution similarly well. In order to describe the mean SED, both models require specific values of the maximum Lorentz factor γmax, which differ by roughly two orders of magnitude. The synchrotron self-Compton model suggests that electrons are accelerated to γmax ∼ 500, while cooled synchrotron model requires acceleration up to γmax ∼ 5 × 104. The synchrotron self-Compton scenario requires electron densities of 1010 cm−3 that are much larger than typical ambient densities in the accretion flow. Furthermore, it requires a variation of the particle density that is inconsistent with the average mass-flow rate inferred from polarization measurements and can therefore only be realized in an extraordinary accretion event. In contrast, assuming a source size of 1 RS, the cooled synchrotron scenario can be realized with densities and magnetic fields comparable with the ambient accretion flow. For both models, the temporal evolution is regulated through the maximum acceleration factor γmax, implying that sustained particle acceleration is required to explain at least a part of the temporal evolution of the flare.

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Language(s): eng - English
 Dates: 2021-10-05
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1051/0004-6361/202140981
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: France : EDP Sciences S A
Pages: - Volume / Issue: 654 Sequence Number: A22 Start / End Page: - Identifier: ISSN: 1432-0746
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1