[en] We present a study of the average X-ray spectral properties of the sources detected by the NuSTAR extragalactic survey, comprising observations of the Extended Chandra Deep Field South (E-CDFS), Extended Groth Strip (EGS), and the Cosmic Evolution Survey (COSMOS). The sample includes 182 NuSTAR sources (64 detected at 8–24 keV), with 3–24 keV fluxes ranging between $f_{3\text{--}24\mathrm{k}\mathrm{e}\mathrm{V}}\approx <!--\; ???\; -->{10}^{-<!--\; ???\; -->14}$ and 6 × 10⁻¹³ erg cm⁻² s⁻¹ ($f_{8\text{--}24\mathrm{k}\mathrm{e}\mathrm{V}}\approx <!--\; ???\; -->3\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->14}\text{--}3\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->13}$ erg cm⁻² s⁻¹) and redshifts in the range of $z=0.04\text{--}3.21$. We produce composite spectra from the Chandra + NuSTAR data ($E\approx <!--\; ???\; -->2\text{--}40\mathrm{k}\mathrm{e}\mathrm{V}$, rest frame) for all the sources with redshift identifications (95%) and investigate the intrinsic, average spectra of the sources, divided into broad-line (BL) and narrow-line (NL) active galactic nuclei (AGNs), and also in different bins of X-ray column density and luminosity. The average power-law photon index for the whole sample is $\mathrm{\Gamma <!--\; ??\; -->}={1.65}_{-<!--\; ???\; -->0.03}^{+0.03}$, flatter than the $\mathrm{\Gamma <!--\; ??\; -->}\approx <!--\; ???\; -->1.8$ typically found for AGNs. While the spectral slope of BL and X-ray unabsorbed AGNs is consistent with the typical values ($\mathrm{\Gamma <!--\; ??\; -->}={1.79}_{-<!--\; ???\; -->0.01}^{+0.01}$), a significant flattening is seen in NL AGNs and heavily absorbed sources ($\mathrm{\Gamma <!--\; ??\; -->}={1.60}_{-<!--\; ???\; -->0.05}^{+0.08}$ and $\mathrm{\Gamma <!--\; ??\; -->}={1.38}_{-<!--\; ???\; -->0.12}^{+0.12}$, respectively), likely due to the effect of absorption and to the contribution from the Compton reflection component to the high-energy flux ($E><!--\; >\; -->10$ keV). We find that the typical reflection fraction in our spectra is $R\approx <!--\; ???\; -->0.5$ (for $\mathrm{\Gamma <!--\; ??\; -->}=1.8$), with a tentative indication of an increase of the reflection strength with X-ray column density. While there is no significant evidence for a dependence of the photon index on X-ray luminosity in our sample, we find that $R$ decreases with luminosity, with relatively high levels of reflection ($R\approx <!--\; ???\; -->1.2$) for $L_{10\text{--}40\mathrm{k}\mathrm{e}\mathrm{V}}<<!--\; <\; -->{10}^{44}$ erg s⁻¹ and $R\approx <!--\; ???\; -->0.3$ for $L_{10\text{--}40\mathrm{k}\mathrm{e}\mathrm{V}}><!--\; >\; -->{10}^{44}$ erg s⁻¹ AGNs, assuming a fixed spectral slope of $\mathrm{\Gamma <!--\; ??\; -->}=1.8$.

[en] We present the results of deep Chandra imaging of the central region of the Extended Groth Strip, the AEGIS-X Deep (AEGIS-XD) survey. When combined with previous Chandra observations of a wider area of the strip, AEGIS-X Wide (AEGIS-XW), these provide data to a nominal exposure depth of 800 ks in the three central ACIS-I fields, a region of approximately 0.29 deg². This is currently the third deepest X-ray survey in existence; a factor $\sim <!--\; ???\; -->2-<!--\; ???\; -->3$ shallower than the Chandra Deep Fields (CDFs), but over an area ∼3 times greater than each CDF. We present a catalog of 937 point sources detected in the deep Chandra observations, along with identifications of our X-ray sources from deep ground-based, Spitzer, GALEX, and Hubble Space Telescope imaging. Using a likelihood ratio analysis, we associate multiband counterparts for 929/937 of our X-ray sources, with an estimated 95% reliability, making the identification completeness approximately 94% in a statistical sense. Reliable spectroscopic redshifts for 353 of our X-ray sources are available predominantly from Keck (DEEP2/3) and MMT Hectospec, so the current spectroscopic completeness is ∼38%. For the remainder of the X-ray sources, we compute photometric redshifts based on multiband photometry in up to 35 bands from the UV to mid-IR. Particular attention is given to the fact that the vast majority the X-ray sources are active galactic nuclei and require hybrid templates. Our photometric redshifts have mean accuracy of $\mathrm{\sigma <!--\; ??\; -->}=0.04$ and an outlier fraction of approximately 5%, reaching $\mathrm{\sigma <!--\; ??\; -->}=0.03$ with less than 4% outliers in the area covered by CANDELS . The X-ray, multiwavelength photometry, and redshift catalogs are made publicly available.

[en] We report Nuclear Spectroscopic Telescope Array (NuSTAR) observations of NuSTAR J033202-2746.8, a heavily obscured, radio-loud quasar detected in the Extended Chandra Deep Field-South, the deepest layer of the NuSTAR extragalactic survey (∼400 ks, at its deepest). NuSTAR J033202-2746.8 is reliably detected by NuSTAR only at E > 8 keV and has a very flat spectral slope in the NuSTAR energy band (Γ=0.55_−0.64^+0.62; 3-30 keV). Combining the NuSTAR data with extremely deep observations by Chandra and XMM-Newton (4 Ms and 3 Ms, respectively), we constrain the broad-band X-ray spectrum of NuSTAR J033202-2746.8, indicating that this source is a heavily obscured quasar (N_H=5.6_−0.8^+0.9×10²³ cm^–2) with luminosity L _{10-40 keV} ≈ 6.4 × 10⁴⁴ erg s^–1. Although existing optical and near-infrared (near-IR) data, as well as follow-up spectroscopy with the Keck and VLT telescopes, failed to provide a secure redshift identification for NuSTAR J033202-2746.8, we reliably constrain the redshift z = 2.00 ± 0.04 from the X-ray spectral features (primarily from the iron K edge). The NuSTAR spectrum shows a significant reflection component (R=0.55_−0.37^+0.44), which was not constrained by previous analyses of Chandra and XMM-Newton data alone. The measured reflection fraction is higher than the R ∼ 0 typically observed in bright radio-loud quasars such as NuSTAR J033202-2746.8, which has L _{1.4 GHz} ≈ 10²⁷ W Hz^–1. Constraining the spectral shape of active galactic nuclei (AGNs), including bright quasars, is very important for understanding the AGN population, and can have a strong impact on the modeling of the X-ray background. Our results show the importance of NuSTAR in investigating the broad-band spectral properties of quasars out to high redshift.