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تسجيل مستخدم جديدThe NuSTAR Extragalactic Surveys: X-ray spectroscopic analysis of the bright hard-band selected sample
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We discuss the spectral analysis of a sample of 63 Active Galactic Nuclei (AGN) detected above a limiting flux of $S(8-24$ keV$)=7times10^{-14}$ erg/s/cm$^2$ in the multi-tiered NuSTAR Extragalactic Survey program. The sources span a redshift range z=0-2.1 (median $langle$z$rangle=$0.58). The spectral analysis is performed over the broad 0.5-24 keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at $ >10$ keV to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density ($N_{rm H}$), reflection parameter ($R$) and 10-40 keV luminosity ($L_{X}$). Heavily obscured ($log [N_{rm H}/cm^{-2}]ge23$) and Compton Thick (CT; $log [N_{rm H}/cm^{-2}]ge24$) AGN constitute $sim$25% (15-17 sources) and $sim$2-3% ( 1-2 sources) of the sample, respectively. The observed $N_{rm H}$ distribution fairly agrees with predictions of Cosmic X-ray Background population synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of $N_{H}$, accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to $log [N_{rm H}/cm^{-2}]=20-24$ AGN is poorly constrainted, formally in the range 2-56% (90% upper limit of 66%). We derived a fraction ($f_{abs}$) of obscured AGN ($log [N_{rm H}/cm^{-2}]=22-24$) as a function of $L_{X}$ in agreement with CXBPSM and previous z < 1 X-ray determinations. Furthermore $f_{abs}$ at z=0.1-0.5 and $log (L_{X}/erg$ $s^{-1})approx43.6-44.3$ agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of $R$ with $L_{X}$ (confirmed by our companion paper on stacked spectra) with considerable scatter around the median $R$ values.
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We present a study of the average X-ray spectral properties of the sources detected by the NuSTAR extragalactic survey, comprising observations of the E-CDFS, EGS and COSMOS fields. The sample includes 182 NuSTAR sources (64 detected at 8-24 keV), wi
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We present a catalog of hard X-ray sources in a square-degree region surveyed by NuSTAR in the direction of the Norma spiral arm. This survey has a total exposure time of 1.7 Ms, and typical and maximum exposure depths of 50 ks and 1 Ms, respectively
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We report on the results of active galactic nuclei (AGNs) detection by NuSTAR performed in three extragalactic survey fields (COSMOS, UDS, ECDFS) in three hard bands, namely H1 (8-16 keV), H2 (16-24 keV) and VH (35-55 keV). The aggregated area of the
surveys is $sim 2.7$ deg$^2$. While a large number of sources is detected in the H1 band (72 at the $97%$ level of reliability), the H2 band directly probing close to the peak of the Cosmic X-ray Background (CXB) returns four significant detections, and two tentative, although not significant, detections are found in the VH band. All the sources detected above 16 keV are also detected at lower energies. We compute the integral number counts for sources in such bands, which show broad consistency with population synthesis models of the CXB. We furthermore identify two Compton-thick AGNs, one in the COSMOS field, associated with a hard and faint Chandra source, and one in the UDS field, never detected in the X-ray band before. Both sources are at the same redshift $z sim 1.25$, which shifts their Compton-hump into the H1 band, and were previously missed in the usually employed NuSTAR bands, confirming the potential of using the H1 band to discover obscured AGNs at $z > 1$ in deep surveys.
NuSTAR observatory, with its 3 - 78 keV broadband spectral coverage, enables the detections of the high-energy cutoff in a number of active galaxies, including several individual radio loud ones. In this work we present systematic and uniform analyse
s of 55 NuSTAR spectra for a large sample of 28 radio galaxies, 20 of which are FR II galaxies. We perform spectral fitting to measure the high energy cut-off $E_{cut}$, photon index $Gamma$, reflection factor R and Fe K$alpha$ line equivalent width. Measurements of $E_{cut}$ are given for 13 sources, and lower limits for the rest. We find those $E_{cut}$ non-detections could primarily be attributed to the obviously smaller net photon counts in their spectra. This indicates that the NuSTAR spectra of the majority of our sample are dominated by the thermal corona emission, and the $E_{cut}$ distribution of the sample is indistinguishable from that of a radio quiet one in literature. The flatter NuSTAR spectra we observed, comparing with radio quiet sources, are thus unlikely due to jet contamination. The radio galaxies also show weaker X-ray reflection (both in R and Fe K$alpha$ line EW) comparing with radio quiet ones. Combining with the radio quiet sample we see a correlation between R and EW, but with considerably large scatter. Notably, the radio loud and quiet sources appear to follow a common $Gamma$ - R correlation trend, supporting the outflowing corona model for both populations in which higher bulk outflowing velocity yields weaker reflection and flatter X-ray slope.
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