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Description
To provide the census of the sources contributing to the X-ray background peak above 10 keV, the Nuclear Spectroscopic Telescope Array (NuSTAR) is performing extragalactic surveys using a three-tier "wedding cake" approach. In their paper, the authors present the NuSTAR survey of the COSMOS field, the medium sensitivity, and medium area "tier",covering 1.7 deg<sup>2</sup> and overlapping with both Chandra and XMM-Newton data. This survey consists of 121 NuSTAR observations for a total exposure of ~3 Ms. To fully exploit these data, the authors developed a new detection strategy, carefully tested through extensive simulations. The survey sensitivity at 20% completeness is 5.9, 2.9, and 6.4 x 10<sup>-14</sup> erg cm<sup>-2</sup> s<sup>-1</sup> in the 3-24, 3-8 and 8-24 keV bands, respectively. By combining detections in 3 bands, the survey consists of a sample of 91 NuSTAR sources with luminosities ~ 10<sup>42</sup> - 10<sup>45.5</sup> erg s<sup>-1</sup>and redshifts z ~ 0.04-2.5. Thirty-two sources are detected in the 8-24 keV band with fluxes ~100 times fainter than sources detected by Swift-BAT. Of the 91 detections, all but 4 are associated with a Chandra and/or XMM-Newton point-like counterpart. One source is associated with an extended lower energy X-ray source. The authors present the X-ray (hardness ratio and luminosity)and optical-to-X-ray properties. The observed fraction of candidate Compton-thick active galactic nuclei measured from the hardness ratio is between 13% - 20%. In their paper, the authors discuss the spectral properties of the source named NuSTAR J100259+0220.5 (source number 330) at a redshift z = 0.044, which has the highest hardness ratio in the entire sample. The measured column density exceeds 10<sup>24</sup> cm<sup>-2</sup>, implying the source is Compton-thick. This source was not previously recognized as such without the data at energies >10 keV. This table was created by the HEASARC in August 2015 based on the the machine-readable versions of Table 5 (the COSMOS Field NuSTAR source catalog) that was obtained from the ApJ web site. This is a service provided by NASA HEASARC .
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