A Caltech Library Service

NuSTAR Detection of High-energy X-Ray Emission and Rapid Variability from Sagittarius A* Flares

Barrière, Nicolas M. and Tomsick, John A. and Baganoff, Frederick K. and Boggs, Steven E. and Christensen, Finn E. and Craig, William W. and Dexter, Jason and Grefenstette, Brian and Hailey, Charles J. and Harrison, Fiona A. and Madsen, Kristin K. and Mori, Kaya and Stern, Daniel and Zhang, William W. and Zhang, Shuo and Zoglauer, Andreas (2014) NuSTAR Detection of High-energy X-Ray Emission and Rapid Variability from Sagittarius A* Flares. Astrophysical Journal, 786 (1). Art. No. 46. ISSN 0004-637X. doi:10.1088/0004-637X/786/1/46.

PDF - Published Version
See Usage Policy.

PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Sagittarius A* harbors the supermassive black hole that lies at the dynamical center of our Galaxy. Sagittarius A* spends most of its time in a low luminosity emission state but flares frequently in the infrared and X-ray, increasing up to a few hundred fold in brightness for up to a few hours at a time. The physical processes giving rise to the X-ray flares are uncertain. Here we report the detection with the NuSTAR observatory in Summer and Fall 2012 of four low to medium amplitude X-ray flares to energies up to 79 keV. For the first time, we clearly see that the power-law spectrum of Sagittarius A* X-ray flares extends to high energy, with no evidence for a cutoff. Although the photon index of the absorbed power-law fits are in agreement with past observations, we find a difference between the photon index of two of the flares (significant at the 95% confidence level). The spectra of the two brightest flares (~55 times quiescence in the 2-10 keV band) are compared to simple physical models in an attempt to identify the main X-ray emission mechanism, but the data do not allow us to significantly discriminate between them. However, we confirm the previous finding that the parameters obtained with synchrotron models are, for the X-ray emission, physically more reasonable than those obtained with inverse Compton models. One flare exhibits large and rapid (<100 s) variability, which, considering the total energy radiated, constrains the location of the flaring region to be within ~10 Schwarzschild radii of the black hole.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle
Barrière, Nicolas M.0000-0001-9407-9490
Tomsick, John A.0000-0001-5506-9855
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Dexter, Jason0000-0003-3903-0373
Grefenstette, Brian0000-0002-1984-2932
Harrison, Fiona A.0000-0003-2992-8024
Madsen, Kristin K.0000-0003-1252-4891
Mori, Kaya0000-0002-9709-5389
Stern, Daniel0000-0003-2686-9241
Zhang, William W.0000-0002-1426-9698
Zhang, Shuo0000-0002-2967-790X
Zoglauer, Andreas0000-0001-9067-3150
Additional Information:© 2014 The American Astronomical Society. Received 2013 August 16; accepted 2014 March 11; published 2014 April 15. 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). The authors thank S. Nayakshin, S. Markoff, A. Eckart, G. Trap, M. Wardle, and F. Yusef-Zadeh for useful discussions. We also thank the Chandra Sgr A* XVP collaboration for information on absence of X-ray transients before and after the flares reported here. Facility: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:accretion, accretion disks; Galaxy: center; stars: black holes; stars: flare; stars: individual (Sgr A*); X-rays: general
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2014-57
Issue or Number:1
Record Number:CaltechAUTHORS:20140618-092849218
Persistent URL:
Official Citation:NuSTAR Detection of High-energy X-Ray Emission and Rapid Variability from Sagittarius A Flares Nicolas M. Barrière et al. 2014 ApJ 786 46
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46324
Deposited By: Tony Diaz
Deposited On:18 Jun 2014 19:29
Last Modified:10 Nov 2021 17:23

Repository Staff Only: item control page