The NuSTAR Hard X-Ray Survey of the Norma Arm Region


Francesca M. Fornasini, University of California, Berkeley
John A. Tomsick, Space Sciences Laboratory at UC Berkeley
Jaesub Hong, Harvard-Smithsonian Center for Astrophysics
Eric V. Gotthelf, Columbia University
Franz Bauer, Pontificia Universidad Católica de Chile
Farid Rahoui, European Southern Observatory
Daniel Stern, Jet Propulsion Laboratory
Arash Bodaghee, Georgia College & State University
Jeng Lun Chiu, Space Sciences Laboratory at UC Berkeley
Maïca Clavel, Space Sciences Laboratory at UC Berkeley
Jesús Corral-Santana, Pontificia Universidad Católica de Chile
Charles J. Hailey, Columbia University
Roman A. Krivonos, Space Sciences Laboratory at UC Berkeley
Kaya Mori, Columbia University
David M. Alexander, Durham University
Didier Barret, Universite Paul Sabatier Toulouse III
Steven E. Boggs, Space Sciences Laboratory at UC Berkeley
Finn E. Christensen, Technical University of Denmark
William W. Craig, Space Sciences Laboratory at UC Berkeley
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
Allan Hornstrup, Technical University of Denmark
Takao Kitaguchi, Hiroshima University
J. E. Koglin, Kavli Institute for Particle Astrophysics and Cosmology
Kristin K. Madsen, California Institute of Technology
Peter H. Mao, California Institute of Technology
Hiromasa Miyasaka, California Institute of Technology
Matteo Perri, California Institute of Technology
Michael J. Pivovaroff, Lawrence Livermore National Laboratory
Simonetta Puccetti, del Politecnico snc
Vikram Rana, California Institute of Technology

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Astrophysical Journal, Supplement Series


We present a catalog of hard X-ray sources in a square-degree region surveyed by the Nuclear Spectroscopic Telescope Array (NuSTAR) in the direction of the Norma spiral arm. This survey has a total exposure time of 1.7 Ms, and the typical and maximum exposure depths are 50 ks and 1 Ms, respectively. In the area of deepest coverage, sensitivity limits of 5 ×10-14 and 4 ×10-14 erg s-1 cm-2 in the 3-10 and 10-20 keV bands, respectively, are reached. Twenty-eight sources are firmly detected, and 10 are detected with low significance; 8 of the 38 sources are expected to be active galactic nuclei. The three brightest sources were previously identified as a low-mass X-ray binary, high-mass X-ray binary, and pulsar wind nebula. Based on their X-ray properties and multiwavelength counterparts, we identify the likely nature of the other sources as two colliding wind binaries, three pulsar wind nebulae, a black hole binary, and a plurality of cataclysmic variables (CVs). The CV candidates in the Norma region have plasma temperatures of ≈10-20 keV, consistent with the Galactic ridge X-ray emission spectrum but lower than the temperatures of CVs near the Galactic center. This temperature difference may indicate that the Norma region has a lower fraction of intermediate polars relative to other types of CVs compared to the Galactic center. The NuSTAR logN-logS distribution in the 10-20 keV band is consistent with the distribution measured by Chandra at 2-10 keV if the average source spectrum is assumed to be a thermal model with kT ≈ 15 keV, as observed for the CV candidates.

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