NuSTAR detection of high-energy X-ray emission and rapid variability from Sagittarius A* flares

Abstract

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 cut off. 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.

arXiv comment24 pages, 10 figures. Accepted for publication in ApJ

References in corpus (45)

• On the Absorption of X-rays in the Interstellar Medium
• The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• Monitoring stellar orbits around the Massive Black Hole in the Galactic Center
• Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits
• The Proper Motion of Sgr A*: II. The Mass of Sgr A*
• Nonthermal Electrons in Radiatively Inefficient Accretion Flow Models of Sagittarius A*
• Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre
• Studies in Astronomical Time Series Analysis. VI. Bayesian Block Representations
• Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre
• Advection-Dominated Accretion Model of Sagittarius A*: Evidence for a Black Hole at the Galactic Center
• Dissecting X-ray-emitting Gas around the Center of our Galaxy
• The Nature of the 10 Kilosecond X-ray Flare in Sgr A*
• The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
• An X-ray, IR, and Submillimeter Flare of Sagittarius A*
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• Rapid variability in the synchrotron self Compton model for blazars
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• Evidence for X-ray synchrotron emission from simultaneous mid-IR to X-ray observations of a strong Sgr A* flare
• Polarimetry of near-infrared flares from Sagittarius A*
• A Chandra/HETGS Census of X-ray Variability From Sgr A* During 2012
• Magnetically Driven Accretion Flows in the Kerr Metric II: Structure of the Magnetic Field
• On The Nature of the Variable Infrared Emission from Sgr A*
• First Simultaneous NIR/X-ray Detection of a Flare from SgrA*
• Evidence for Low Black Hole Spin and Physically Motivated Accretion Models from Millimeter VLBI Observations of Sagittarius A*
• Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
• Sagittarius A* Accretion Flow and Black Hole Parameters from General Relativistic Dynamical and Polarized Radiative Modeling
• Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*
• A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft $\gamma$-ray and Sub-millimeter Emission
• A Magnetohydrodynamic Model for the Formation of Episodic Jets
• X-ray hiccups from SgrA* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day
• A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton Photon Imaging Cameras
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Simultaneous Multi-Wavelength Observations of Sgr A* during 2007 April 1-11
• Source-intrinsic near-infrared properties of Sgr A*: Total intensity measurements
• Time Dependent Models of Flares from Sagittarius A*
• Tidal effects on small bodies by massive black holes
• Prospects for testing the nature of Sgr A*'s NIR flares on the basis of current VLT- and future VLTI-observations
• On the tidal evolution of the orbits of low-mass satellites around black holes
• A Possible Rossby Wave Instability Origin for the Flares in Sagittarius A*
• Sgr A* flares: tidal disruption of asteroids and planets?
• Repeated X-ray Flaring Activity in Sagittarius A*
• Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sgr A*
• The X-ray flaring properties of Sgr A* during six years of monitoring with Swift
• An Inverse Compton Scattering Origin of X-ray Flares from Sgr A*

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