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

Francesca M. Fornasini, John A. Tomsick, JaeSub Hong, Eric V. Gotthelf, Franz E. Bauer, Farid Rahoui, Daniel Stern, Arash Bodaghee, Jeng-Lun Chiu, Maica Clavel, Jesus Corral-Santana, Charles J. Hailey, Roman A. Krivonos, Kaya Mori, David M. Alexander, Didier Barret, Steven E. Boggs, Finn Erland Christensen, William Craig, Karl ForsterPaolo Giommi, Brian W. Grefenstette, Fiona A. Harrison, Allan Hornstrup, Takao Kitaguchi, J. E. Koglin, Kristin K. Madsen, Peter H. Mao, Hiromasa Miyasaka, Matteo Perri, Michael J. Pivovaroff, Simonetta Puccetti, Vikram Rana, Niels Jørgen Stenfeldt Westergaard, William Zhang

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Abstract

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.
Original languageEnglish
Article number33
JournalAstrophysical Journal Supplement Series
Volume229
Issue number2
Number of pages39
ISSN0067-0049
DOIs
Publication statusPublished - 2017

Cite this

Fornasini, F. M., Tomsick, J. A., Hong, J., Gotthelf, E. V., Bauer, F. E., Rahoui, F., ... Zhang, W. (2017). The NuSTAR Hard X-Ray Survey of the Norma Arm Region. Astrophysical Journal Supplement Series, 229(2), [33]. https://doi.org/10.3847/1538-4365/aa61fc