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Sagittarius A* High Energy X-ray Flare Properties During NuSTAR Monitoring of the Galactic Center from 2012 to 2015

Zhang, Shuo and Baganoff, Frederick K. and Ponti, Gabriele and Neilsen, Joseph and Tomsick, John A. and Dexter, Jason and Clavel, Maïca and Markoff, Sera and Hailey, Charles J. and Mori, Kaya and Barrière, Nicolas M. and Nowak, Michael A. and Boggs, Steven E. and Christensen, Finn E. and Craig, William W. and Grefenstette, Brian W. and Harrison, Fiona A. and Madsen, Kristin K. and Stern, Daniel and Zhang, William W. (2017) Sagittarius A* High Energy X-ray Flare Properties During NuSTAR Monitoring of the Galactic Center from 2012 to 2015. Astrophysical Journal, 843 (2). Art. No. 96. ISSN 0004-637X. doi:10.3847/1538-4357/aa74e8.

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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_(3-79 keV) ~(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 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 quiescent-state 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).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Zhang, Shuo0000-0002-2967-790X
Ponti, Gabriele0000-0003-0293-3608
Neilsen, Joseph0000-0002-8247-786X
Tomsick, John A.0000-0001-5506-9855
Dexter, Jason0000-0003-3903-0373
Clavel, Maïca0000-0003-0724-2742
Markoff, Sera0000-0001-9564-0876
Mori, Kaya0000-0002-9709-5389
Barrière, Nicolas M.0000-0001-9407-9490
Nowak, Michael A.0000-0001-6923-1315
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Grefenstette, Brian W.0000-0002-1984-2932
Harrison, Fiona A.0000-0003-2992-8024
Madsen, Kristin K.0000-0003-1252-4891
Stern, Daniel0000-0003-2686-9241
Zhang, William W.0000-0002-1426-9698
Additional Information:© 2017 The American Astronomical Society. Received 2017 April 12; revised 2017 May 19; accepted 2017 May 22; published 2017 July 10. This work was supported under NASA Contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). S.Z. acknowledges support by NASA Headquarters under the NASA Earth and Space Science Fellowship Program—Grant "NNX13AM31H." J.N. acknowledges funding from NASA through the Einstein Postdoctoral Fellowship, grant PF2-130097, awarded by the CXC, which is operated by the SAO for NASA under contract NAS8-03060. G.P. acknowledges support by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OR 1604) and the Max Planck Society. We thank all members of the Chandra Sgr A* XVP collaboration (
Group:Space Radiation Laboratory, NuSTAR, Astronomy Department
Funding AgencyGrant Number
NASA Einstein FellowshipPF2-130097
Bundesministerium für Wirtschaft und Technologie (BMWi)FKZ 50 OR 1604
Max Planck SocietyUNSPECIFIED
Subject Keywords:accretion, accretion disks – quasars: supermassive black holes – radiation mechanisms: non-thermal – X-rays: individual (sgra)
Issue or Number:2
Record Number:CaltechAUTHORS:20170524-092936920
Persistent URL:
Official Citation:Shuo Zhang et al 2017 ApJ 843 96
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77701
Deposited By: Joy Painter
Deposited On:24 May 2017 16:51
Last Modified:15 Nov 2021 17:33

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