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|a dc
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|a Ponti, Gabriele
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|a MIT Kavli Institute for Astrophysics and Space Research
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|a Zhang, Shuo
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|a Baganoff, Frederick K
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|a Neilsen, Joseph M. G.
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|a Nowak, Michael A
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|a Tomsick, John A.
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|a Dexter, Jason
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|a Clavel, Maïca
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|a Markoff, Sera
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|a Hailey, Charles J.
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|a Mori, Kaya
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|a Barrière, Nicolas M.
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|a Boggs, Steven E.
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|a Christensen, Finn E.
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|a Craig, William W.
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|a Grefenstette, Brian W.
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|a Harrison, Fiona A.
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|a Madsen, Kristin K.
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|a Stern, Daniel
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|a Zhang, William W.
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|a Zhang, Shuo
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|a Baganoff, Frederick K
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|a Neilsen, Joseph M. G.
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|a Nowak, Michael A.
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|a Sagittarius A* High-energy X-Ray Flare Properties during NuStar Monitoring of the Galactic Center from 2012 to 2015
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|b IOP Publishing,
|c 2017-11-20T18:19:51Z.
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|z Get fulltext
|u http://hdl.handle.net/1721.1/112245
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|a 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 ≃1 Ms. We found a total of 10 X-ray flares detected in the NuSTAR observation window, with luminosities in the range of L[subscript 3-79 keV] ∼ (0.2-4.0) × 10[superscript 35] erg s [superscript -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 5σ significance, showing a range of photon indices (Γ ∼ 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 Γ = 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[subscript X[subscript q], 10-79 keV] ≤ (2.9 ± 0.2) × 10 [superscript 34] erg s[superscript -1] .
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|a United States. National Aeronautics and Space Administration (Contract NNG08FD60C)
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|a United States. National Aeronautics and Space Administration. Earth and Space Science Fellowship Program (Grant NNX13AM31H)
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|a United States. National Aeronautics and Space Administration. Einstein Postdoctoral Fellowship Award (Grant PF2-130097)
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|a Article
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|t The Astrophysical Journal
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