期刊
ASTROPHYSICAL JOURNAL
卷 843, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.3847/1538-4357/aa74e8
关键词
accretion, accretion disks; quasars: supermassive black holes; radiation mechanisms: non-thermal; X-rays: individual (sgra)
资金
- NASA [NNG08FD60C, NAS8-03060]
- National Aeronautics and Space Administration
- NASA Headquarters under the NASA Earth and Space Science Fellowship [NNX13AM31H]
- NASA through the Einstein Postdoctoral Fellowship - CXC [PF2-130097]
- Bundesministerium fur Wirtschaft und Technologie/Deutsches Zentrum fur Luft- und Raumfahrt (BMWI/DLR) [FKZ 50 OR 1604]
- Max Planck Society
Understanding the origin of the flaring activity from the Galactic center supermassive black hole Sagittarius. A* is a major scientific goal of the NuSTAR Galactic plane survey campaign. We report on the data obtained between 2012 July and 2015 April, including 27 observations on Sgr A*, with a total exposure of similar or equal to 1 Ms. We found a total of 10 X-ray flares detected in the NuSTAR observation window, with luminosities in the range of L3-79keV similar to (0.2-4.0) X 10(35) erg s(-1). With this largest hard X-ray Sgr A* flare data set to date, we studied the flare spectral properties. Seven flares are detected above 5 sigma significance, showing a range of photon indices (Gamma similar to 2.0-2.8) with typical uncertainties of +/- 0.5 (90% confidence level). We found no significant spectral hardening for brighter flares, as indicated by a smaller sample. The accumulation of all of the flare spectra in 1-79 keV can be well fit with an absorbed power-law model with Gamma = 2.2 +/- 0.1, and does not require the existence of a spectral break. The lack of variation in the X-ray spectral index with luminosity would point to a single mechanism for the flares and is consistent with the synchrotron scenario. Lastly, we present the quiescentstate spectrum of Sgr A*, and derive an upper limit on the quiescent luminosity of Sgr A* above 10 keV to be L-Xq,(10-79) (keV) <= (2.9 +/- 0.2) X 10(34) erg s(-1).
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