The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

Abstract

We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S 8 24 keV 7 10 14 =´-( -) erg s cm 1 2 --in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z 0 2.1 = -(median z 0.58 á ñ = ). 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 H ), reflection parameter (R), and 10-40keV luminosity (L X ). Heavily obscured ( N log cm 23AGN constitute ∼25% (15-17 sources) and ∼2-3% (1-2 sources) of the sample, respectively. The observed N H distribution agrees fairly well 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 N log cm 20 24AGN is poorly constrained, formally in the range 2-56% (90% upper limit of 66%). We derived a fraction ( f abs ) of obscured AGN ( N log cm 22 24as 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 L log erg s 43.6 44.3agrees 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.

The NuSTAR Extragalactic Surveys: Source Catalog and the Compton-thick Fraction in the UDS Field

“…Indeed, Lansbury et al (2017a) find that the low-redshift (z<0.07) CT fraction is unexpectedly high (∼30%) compared to model predictions, while the UDS sample covers much higher redshifts, since our CT candidates are almost all between 1<z<2, and broadly agrees with model predictions (for 0<z<3). On the other hand, Zappacosta et al (2018) and z 0.58 á ñ = , finding a CT fraction between 1% and 8%, which is consistent with our result. However, the right panel of Figure 8 shows that roughly half of our sources reliably detected in the full band have F-band fluxes lower than their H-band cut, implying an even lower H-band flux for our sources (a factor of 7-10 with respect to the sources selected in Zappacosta et al 2018).…”

“…On the other hand, Zappacosta et al (2018) and z 0.58 á ñ = , finding a CT fraction between 1% and 8%, which is consistent with our result. However, the right panel of Figure 8 shows that roughly half of our sources reliably detected in the full band have F-band fluxes lower than their H-band cut, implying an even lower H-band flux for our sources (a factor of 7-10 with respect to the sources selected in Zappacosta et al 2018). This is also confirmed by the spectral analysis performed.…”

“…Following the methodology of Zappacosta et al (2018), for any source and pointing in which it is found, we extract the number of counts, background counts, and average exposure in the F band for a range of extraction radii. This allows us to get a signal-to-noise ratio (S/N) profile as a function of extraction radius for each pointing and each FPM; the single S/N(r) profiles are then averaged together, weighted with the exposure time at the position of the source in every observation.…”

Examining the physical conditions of a warm corona in active galactic nuclei accretion discs

“…It is interesting to consider if such unusual spectra may be related to ones observed in AGNs, in particular Narrow-Line Seyfert 1 galaxies (NLS1s; Gallo 2018). Figure 8 plots the h f = 0.7 spectrum from the n H = 2 × 10 14 cm −3 , τ T = 10 series of models, but we have now added the illuminating power-law to the reflection spectrum, so that R, the reflection fraction, is 0.7, consistent with typical values observed in AGNs (e.g., Zappacosta et al 2018). The spectrum shown in the figure has a steep hard X-ray spectrum with a 2-10 keV photon-index of 3.04, an ionised Fe Kα line and deep iron edge, all properties similar to those observed in several NLS1s (e.g., 1H 0707-495; Ballantyne et al 2001a;Boller et al 2002;Zoghbi et al 2010;Fabian et al 2012;Liu et al 2016).…”

Accretion History of AGNs. II. Constraints on AGN Spectral Parameters Using the Cosmic X-Ray Background

“…This model takes Compton-reflection by the torus into account, and prescribes an overall AGN spectrum similar to the above model, with cutoffpl instead of pexmon. As observed by Dadina (2008), Beckmann et al (2009), Ricci et al (2017) and Zappacosta et al (2018), unobscured objects usually have a higher reflection fraction than obscured objects, possibly due to reflection by the accretion disk (e.g., Beckmann et al 2009), although the proportion of reflected to transmitted component for ob-scured objects is higher. This is why we include the pexmon model, which accounts for reflection due to a slab geometry like an accretion disk, which is not modeled as part of the conical geometry of borus02.…”