NuSTAR hard X-ray survey of the Galactic Center region. II. X-ray point sources


Jaesub Hong, Harvard-Smithsonian Center for Astrophysics
Kaya Mori, Columbia University
Charles J. Hailey, Columbia University
Melania Nynka, Columbia University
Shuo Zhang, Columbia University
Eric Gotthelf, Columbia University
Francesca M. Fornasini, University of California, Berkeley
Roman Krivonos, Space Research Institute of the Russian Academy of Sciences
Franz Bauer, Pontificia Universidad Católica de Chile
Kerstin Perez, Haverford College
John A. Tomsick, Space Sciences Laboratory at UC Berkeley
Arash Bodaghee, Georgia College & State University
Jeng Lun Chiu, Space Sciences Laboratory at UC Berkeley
Maïca Clavel, Space Sciences Laboratory at UC Berkeley
Daniel Stern, Jet Propulsion Laboratory
Jonathan E. Grindlay, Harvard-Smithsonian Center for Astrophysics
David M. Alexander, Durham University
Tsuguo Aramaki, SLAC National Accelerator Laboratory
Frederick K. Baganoff, MIT Kavli Institute for Astrophysics and Space Research
Didier Barret, Universite Paul Sabatier Toulouse III
Nicolas Barrière, Space Sciences Laboratory at UC Berkeley
Steven E. Boggs, Space Sciences Laboratory at UC Berkeley
Alicia M. Canipe, Columbia University
Finn E. Christensen, Universite Paul Sabatier Toulouse III
William W. Craig, Space Sciences Laboratory at UC Berkeley
Meera A. Desai, Columbia University
Karl Forster, California Institute of Technology
Paolo Giommi, del Politecnico snc
Brian W. Grefenstette, California Institute of Technology
Fiona A. Harrison, California Institute of Technology
Dooran Hong, Columbia University
Allan Hornstrup, Technical University of Denmark
Takao Kitaguchi, Hiroshima University

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Astrophysical Journal


We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg region around Sgr A∗ with a total exposure of 1.7 Ms, and 7 sources in the Sgr B2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ∼4× and ∼8 × 10 erg s at the GC (8 kpc) in the 3-10 and 10-40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the Sgr A diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%-60%). Both spectral analysis and logN-logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT > 20 keV on average for a single temperature thermal plasma model or an average photon index of Γ = 1.5-2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.

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