A NuSTAR and Chandra study of late stage galaxy cluster merger CL 0217+70 and its tell-tale radio halo

Galaxie

The Nustar Extragalactic Surveys: Overview and Catalog from the COSMOS Field

To provide the census of the sources contributing to the X-ray background peak above 10 keV, Nuclear Spectroscopic Telescope Array (NuSTAR) is performing extragalactic surveys using a three-tier "wedding cake" approach. We present the NuSTAR survey of the COSMOS field, the medium sensitivity, and medium area tier, covering 1.7 deg2 and overlapping with both Chandra and XMM-Newton data. This survey consists of 121 observations for a total exposure of ~3 Ms. To fully exploit these data, we developed a new detection strategy, carefully tested through extensive simulations. The survey sensitivity at 20% completeness is 5.9, 2.9, and 6.4 × 10−14 $\mathrm{erg}\;{\mathrm{cm}}^{-2}\;{{\rm{s}}}^{-1}$ in the 3–24, 3–8, and 8–24 keV bands, respectively. By combining detections in 3 bands, we have a sample of 91 NuSTAR sources with 1042–1045.5 $\mathrm{erg}\;{{\rm{s}}}^{-1}$ luminosities and redshift 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. We 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%. We discuss the spectral properties of NuSTAR J100259+0220.6 (ID 330) at z = 0.044, with the highest hardness ratio in the entire sample. The measured column density exceeds 1024 cm−2, implying the source is Compton-thick. This source was not previously recognized as such without the >10 keV data

The NuSTAR Extragalactic Survey: First Direct Measurements of the \gsim10 KeV X-Ray Luminosity Function for Active Galactic Nuclei at z > 0.1

We present the first direct measurements of the rest-frame 10–40 keV X-ray luminosity function (XLF) of active galactic nuclei (AGNs) based on a sample of 94 sources at 0.1 < z < 3, selected at 8–24 keV energies from sources in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic survey program. Our results are consistent with the strong evolution of the AGN population seen in prior, lower-energy studies of the XLF. However, different models of the intrinsic distribution of absorption, which are used to correct for selection biases, give significantly different predictions for the total number of sources in our sample, leading to small, systematic differences in our binned estimates of the XLF. Adopting a model with a lower intrinsic fraction of Compton-thick sources and a larger population of sources with column densities ${N}_{{\rm{H}}}\sim {10}^{23-24}$ cm−2 or a model with stronger Compton reflection component (with a relative normalization of R ~ 2 at all luminosities) can bring extrapolations of the XLF from 2–10 keV into agreement with our NuSTAR sample. Ultimately, X-ray spectral analysis of the NuSTAR sources is required to break this degeneracy between the distribution of absorbing column densities and the strength of the Compton reflection component and thus refine our measurements of the XLF. Furthermore, the models that successfully describe the high-redshift population seen by NuSTAR tend to over-predict previous, high-energy measurements of the local XLF, indicating that there is evolution of the AGN population that is not fully captured by the current models

NuSTAR Reveals an Intrinsically X-ray Weak Broad Absorption Line Quasar in the Ultraluminous Infrared Galaxy Markarian 231

We present high-energy (3-30 keV) NuSTAR observations of the nearest quasar, the ultraluminous infrared galaxy (ULIRG) Markarian 231 (Mrk 231), supplemented with new and simultaneous low-energy (0.5-8 keV) data from Chandra. The source was detected, though at much fainter levels than previously reported, likely due to contamination in the large apertures of previous non-focusing hard X-ray telescopes. The full band (0.5-30 keV) X-ray spectrum suggests the active galactic nucleus (AGN) in Mrk 231 is absorbed by a patchy and Compton-thin ($N_{\rm H} \sim 1.2^{+0.3}_{-0.3}\times 10^{23}$ cm–2) column. The intrinsic X-ray luminosity (L 0.5 – 30 keV ~ 1.0 × 1043 erg s–1) is extremely weak relative to the bolometric luminosity where the 2-10 keV to bolometric luminosity ratio is ~0.03% compared to the typical values of 2%-15%. Additionally, Mrk 231 has a low X-ray-to-optical power law slope (αOX ~ –1.7). It is a local example of a low-ionization broad absorption line quasar that is intrinsically X-ray weak. The weak ionizing continuum may explain the lack of mid-infrared [O IV], [Ne V], and [Ne VI] fine-structure emission lines which are present in sources with otherwise similar AGN properties. We argue that the intrinsic X-ray weakness may be a result of the super-Eddington accretion occurring in the nucleus of this ULIRG, and may also be naturally related to the powerful wind event seen in Mrk 231, a merger remnant escaping from its dusty cocoon

The NuSTAR Extragalactic Surveys: Initial Results and Catalog from the Extended Chandra Deep Field South

We present the initial results and the source catalog from the Nuclear Spectroscopic Telescope Array (NuSTAR) survey of the Extended Chandra Deep Field South (hereafter, ECDFS)—currently the deepest contiguous component of the NuSTAR extragalactic survey program. The survey covers the full ≈30′ × 30′ area of this field to a maximum depth of ≈360 ks (»220 ks when corrected for vignetting at 3–24 keV), reaching sensitivity limits of » ´ 1.3 10 erg s cm - -- 14 1 2 (3–8 keV), » ´ 3.4 10 erg s cm - -- 14 1 2 (8–24 keV), and » ´ 3.0 10 erg s cm - -- 14 1 2 (3–24 keV). A total of 54 sources are detected over the full field, although five of these are found to lie below our significance threshold once contaminating flux from neighboring (i.e., blended) sources is taken into account. Of the remaining 49 that are significant, 19 are detected in the 8–24 keV band. The 8–24 to 3–8 keV band ratios of the 12 sources that are detected in both bands span the range 0.39–1.7, corresponding to a photon index range of G » - 0.5 2.3, with a median photon index of G = 1.70 0.52. The redshifts of the 49 sources in our main sample span the range z = - 0.21 2.7, and their rest-frame 10–40 keV luminosities (derived from the observed 8–24 keV fluxes) span the range L10 40 keV (0.7 300) 10 erg s »- ´ 43 1 - - , sampling below the “knee” of the X-ray luminosity function out to z ~ - 0.8 1. Finally, we identify one NuSTAR source that has neither a Chandra nor an XMM-Newton counterpart, but that shows evidence of nuclear activity at infrared wavelengths and thus may represent a genuine, new X-ray source detected by NuSTAR in the ECDFS

The NuSTAR extragalactic surveys: The number counts of active galactic nuclei and the resolved fraction of the cosmic X-ray background

We present the 3–8 keV and 8–24 keV number counts of active galactic nuclei (AGNs) identified in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic surveys. NuSTAR has now resolved 33%–39% of the X-ray background in the 8–24 keV band, directly identifying AGNs with obscuring columns up to $\sim {10}^{25}\,{\mathrm{cm}}^{-2}$. In the softer 3–8 keV band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range $5\times {10}^{-15}\,\lesssim$ S(3–8 keV)/$\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,\lesssim \,{10}^{-12}$ probed by NuSTAR. In the hard 8–24 keV band NuSTAR probes fluxes over the range $2\times {10}^{-14}\,\lesssim$ S(8–24 keV)/$\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,\lesssim \,{10}^{-12}$, a factor ~100 fainter than previous measurements. The 8–24 keV number counts match predictions from AGN population synthesis models, directly confirming the existence of a population of obscured and/or hard X-ray sources inferred from the shape of the integrated cosmic X-ray background. The measured NuSTAR counts lie significantly above simple extrapolation with a Euclidian slope to low flux of the Swift/BAT 15–55 keV number counts measured at higher fluxes (S(15–55 keV) gsim 10−11 $\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}$), reflecting the evolution of the AGN population between the Swift/BAT local ($z\lt 0.1$) sample and NuSTAR's $z\sim 1$ sample. CXB synthesis models, which account for AGN evolution, lie above the Swift/BAT measurements, suggesting that they do not fully capture the evolution of obscured AGNs at low redshifts