We present the first catalog and data release of the Swift-BAT AGN Spectroscopic Survey. We analyze optical spectra of the majority of the detected AGNs (77%, 642/836)based on their 14-195 keV ...emission in the 70-month Swift-BAT all-sky catalog. This includes redshift determination, absorption and emission-line measurements, and black hole mass and accretion rate estimates for the majority of obscured and unobscured AGNs (74%, 473/642), with 340 measured for the first time. With ∼90% of sources at , the survey represents a significant advance in the census of hard X-ray-selected AGNs in the local universe. In this first catalog paper, we describe the spectroscopic observations and data sets, and our initial spectral analysis. The FWHMs of the emission lines show broad agreement with the X-ray obscuration (∼94%), such that Sy 1-1.8 have cm−2, and Seyfert 2 have cm−2. Seyfert 1.9, however, show a range of column densities. Compared to narrow-line AGNs in the SDSS, the X-ray-selected AGNs have a larger fraction of dusty host galaxies ( ), suggesting that these types of AGN are missed in optical surveys. Using the O iii λ5007/Hβ and N ii λ6583/H emission-line diagnostic, about half of the sources are classified as Seyferts; ∼15% reside in dusty galaxies that lack an Hβ detection, but for which the upper limits on line emission imply either a Seyfert or LINER, are in galaxies with weak or no emission lines despite high-quality spectra, and a few percent each are LINERS, composite galaxies, H ii regions, or in known beamed AGNs.
We report a new changing-look quasar, WISE J105203.55+151929.5 at z = 0.303, found by identifying highly mid-IR-variable quasars in the Wide-field Infrared Survey Explorer (WISE)/Near-Earth Object ...WISE Reactivation (NEOWISE) data stream. Compared to multiepoch mid-IR photometry of a large sample of SDSS-confirmed quasars, WISE J1052+1519 is an extreme photometric outlier, fading by more than a factor of two at 3.4 and 4.6 m since 2009. Swift target-of-opportunity observations in 2017 show even stronger fading in the soft X-rays compared to the ROSAT detection of this source in 1995, with at least a factor of 15 decrease. We obtained second-epoch spectroscopy with the Palomar telescope in 2017 that, when compared with the 2006 archival SDSS spectrum, reveals that the broad Hβ emission has vanished and that the quasar has become significantly redder. The two most likely interpretations for this dramatic change are source fading or obscuration, where the latter is strongly disfavored by the mid-IR data. We discuss various physical scenarios that could cause such changes in the quasar luminosity over this timescale, and favor changes in the innermost regions of the accretion disk that occur on the thermal and heating/cooling front timescales. We discuss possible physical triggers that could cause these changes, and predict the multiwavelength signatures that could distinguish these physical scenarios.
ABSTRACT We report on high-energy X-ray observations of the Compton-thick Seyfert 2 galaxy NGC 1068 with NuSTAR, which provide the best constraints to date on its >10 keV spectral shape. The NuSTAR ...data are consistent with those from past and current instruments to within cross-calibration uncertainties, and we find no strong continuum or line variability over the past two decades, which is in line with its X-ray classification as a reflection-dominated Compton-thick active galactic nucleus. The combined NuSTAR, Chandra, XMM-Newton, and Swift BAT spectral data set offers new insights into the complex secondary emission seen instead of the completely obscured transmitted nuclear continuum. The critical combination of the high signal-to-noise NuSTAR data and the decomposition of the nuclear and extranuclear emission with Chandra allow us to break several model degeneracies and greatly aid physical interpretation. When modeled as a monolithic (i.e., a single NH) reflector, none of the common Compton reflection models are able to match the neutral fluorescence lines and broad spectral shape of the Compton reflection hump without requiring unrealistic physical parameters (e.g., large Fe overabundances, inconsistent viewing angles, or poor fits to the spatially resolved spectra). A multi-component reflector with three distinct column densities (e.g., with best-fit values of NH of 1.4 × 1023, 5.0 × 1024, and 1025 cm−2) provides a more reasonable fit to the spectral lines and Compton hump, with near-solar Fe abundances. In this model, the higher NH component provides the bulk of the flux to the Compton hump, while the lower NH component produces much of the line emission, effectively decoupling two key features of Compton reflection. We find that 30% of the neutral Fe K line flux arises from >2″ ( 140 pc) and is clearly extended, implying that a significant fraction (and perhaps most) of the <10 keV reflected component arises from regions well outside a parsec-scale torus. These results likely have ramifications for the interpretation of Compton-thick spectra from observations with poorer signal-to-noise and/or more distant objects.
The recent Chandra discovery of extended ∼kiloparsec-scale hard (>3 keV) X-ray emission in nearby Compton-thick (CT) active galactic nuclei (AGN) opens a new window to improving AGN torus modeling ...and investigating how the central supermassive black hole interacts with and impacts the host galaxy. Since there are only a handful of detections so far, we need to establish a statistical sample to determine the ubiquity of the extended hard X-ray emission in CT AGN and quantify the amount and extent of this component. In this paper, we present the spatial analysis results of a pilot Chandra imaging survey of seven nearby ( 0.006 < z < 0.013 ) CT AGN selected from the Swift-BAT spectroscopic AGN survey. We find that five out of the seven CT AGN show extended emission in the 3-7 keV band detected at >3 above the Chandra point-spread function (PSF), with ∼12%-22% of the total emission in the extended components. ESO 137-G034 and NGC 3281 display biconical ionization structures with extended hard X-ray emission reaching kiloparsec scales (∼1.9 and 3.5 kpc in diameter). The other three show extended hard X-ray emission above the PSF out to at least ∼360 pc in radius. We find a trend that a minimum 3-7 keV count rate of 0.01 counts s−1 and total excess fraction >20% are required to detect a prominent extended hard X-ray component. Given that this extended hard X-ray component appears to be relatively common in this uniformly selected CT AGN sample, we further discuss the implications for torus modeling and AGN feedback.
ABSTRACT We have discovered heavy obscuration in the dual active galactic nucleus (AGN) in the Swift/Burst Alert Telescope (BAT) source SWIFT J2028.5+2543 using Nuclear Spectroscopic Telescope Array ...(NuSTAR). While an early XMM-Newton study suggested the emission was mainly from NGC 6921, the superior spatial resolution of NuSTAR above 10 keV resolves the Swift/BAT emission into two sources associated with the nearby galaxies MCG +04-48-002 and NGC 6921 (z = 0.014) with a projected separation of 25.3 kpc (91″). NuSTAR's sensitivity above 10 keV finds both are heavily obscured to Compton-thick levels (NH (1-2) × 1024 cm−2) and contribute equally to the BAT detection ( L 10 − 50 keV int 6 × 1042 erg s−1). The observed luminosity of both sources is severely diminished in the 2-10 keV band ( L 2 − 10 keV obs < 0.1 × L 2 − 10 keV int ), illustrating the importance of >10 keV surveys like those with NuSTAR and Swift/BAT. Compared to archival X-ray data, MCG +04-48-002 shows significant variability (>3) between observations. Despite being bright X-ray AGNs, they are difficult to detect using optical emission-line diagnostics because MCG +04-48-002 is identified as a starburst/composite because of the high rates of star formation from a luminous infrared galaxy while NGC 6921 is only classified as a LINER using line detection limits. SWIFT J2028.5+2543 is the first dual AGN resolved above 10 keV and is the second most heavily obscured dual AGN discovered to date in the X-rays other than NGC 6240.
ABSTRACT BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, ...Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012-2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse Compton emission from nonthermal seed photons originating from within the jet. The passage of four new superluminal very long baseline interferometry knots through the core and two stationary knots about 4 pc downstream accompanied the high flaring in 2012-2013. The seed photons for inverse Compton scattering may arise from the stationary knots and from a Mach disk near the core where relatively slow-moving plasma generates intense nonthermal radiation. The 95 spectral energy distributions obtained on consecutive days form the most densely sampled, broad wavelength coverage for any blazar. The observed spectral energy distributions and multi-waveband light curves are similar to simulated spectral energy distributions and light curves generated with a model in which turbulent plasma crosses a conical shock with a Mach disk.
We present an analysis of a sample of 69 local obscured Swift/Burst Alert Telescope active galactic nuclei (AGNs) with X-ray spectra from NuSTAR and infrared (IR) spectral energy distributions from ...Herschel and WISE. We combine this X-ray and IR phenomenological modeling and find a significant correlation between reflected hard X-ray emission and IR AGN emission, with suggestive indications that this correlation may be stronger than the one between intrinsic hard X-ray and IR emissions. This relation between the IR and reflected X-ray emission suggests that both are the result of the processing of intrinsic emission from the corona and accretion disk by the same structure. We explore the resulting implications on the underlying distribution of covering fraction for all AGNs, by generating mock observables for the reflection parameter and IR luminosity ratio using empirical relations found for the covering fraction with each quantity. We find that the observed distributions of the reflection parameter and IR-to-X-ray ratio are reproduced with broad distributions centered around covering fractions of at least ∼40%-50%, whereas narrower distributions match our observations only when centered around covering fractions of ∼70%-80%. Our results are consistent with both independent estimates of the covering fractions of individual objects and the typical covering fraction obtained on the basis of obscured fractions for samples of AGNs. These results suggest that the level of reprocessing in AGNs, including X-ray reflection, is related in a relatively straightforward way to the geometry of the obscuring material.
We present results from modeling the broadband X-ray spectrum of the Type 1 active galactic nucleus (AGN) 2MASX J193013.80+341049.5 using NuSTAR, Swift, and archival XMM-Newton observations. We find ...this source to be highly X-ray obscured, with column densities exceeding 1023 cm−2 across all epochs of X-ray observations, spanning an 8 yr period. However, the source exhibits prominent broad optical emission lines, consistent with an unobscured Type 1 AGN classification. We fit the X-ray spectra with both phenomenological reflection models and physically motivated torus models to model the X-ray absorption. We examine the spectral energy distribution of this source and investigate some possible scenarios to explain the mismatch between X-ray and optical classifications. We compare the ratio of reddening to X-ray absorbing column density ( / ) and find that 2MASX J193013.80+341049.5 likely has a much lower dust-to-gas ratio relative to the Galactic interstellar medium, suggesting that the broad line region itself could provide the source of extra X-ray obscuration, being composed of low-ionization, dust-free gas.
ABSTRACT We study the geometry of the active galactic nucleus (AGN) obscurer in IRAS 09104+4109, an IR-luminous, radio-intermediate FR-I source at z = 0.442, using infrared data from Spitzer and ...Herschel, X-ray data from NuSTAR, Swift, Suzaku, and Chandra, and an optical spectrum from Palomar. The infrared data imply a total rest-frame 1-1000 m luminosity of 5.5 × 1046 erg s−1 and require both an AGN torus and a starburst model. The AGN torus has an anisotropy-corrected IR luminosity of 4.9 × 1046 erg s−1 and a viewing angle and half-opening angle both of approximately 36° from pole-on. The starburst has a star formation rate of (110 34) M yr−1 and an age of <50 Myr. These results are consistent with two epochs of luminous activity in IRAS 09104+4109: one approximately 150 Myr ago, and one ongoing. The X-ray data suggest a photon index of Γ 1.8 and a line-of-sight column density of NH 5 × 1023 cm−2. This argues against a reflection-dominated hard X-ray spectrum, which would have implied a much higher NH and luminosity. The X-ray and infrared data are consistent with a bolometric AGN luminosity of Lbol ∼ (0.5-2.5) × 1047 erg s−1. The X-ray and infrared data are further consistent with coaligned AGN obscurers in which the line of sight "skims" the torus. This is also consistent with the optical spectra, which show both coronal iron lines and broad lines in polarized but not direct light. Combining constraints from the X-ray, optical, and infrared data suggest that the AGN obscurer is within a vertical height of 20 pc, and a radius of 125 pc, of the nucleus.
Hard X-ray (≥10 keV) observations of active galactic nuclei (AGNs) can shed light on some of the most obscured episodes of accretion onto supermassive black holes. The 70-month Swift/BAT all-sky ...survey, which probes the 14-195 keV energy range, has currently detected 838 AGNs. We report here on the broadband X-ray (0.3-150 keV) characteristics of these AGNs, obtained by combining XMM-Newton, Swift/XRT, ASCA, Chandra, and Suzaku observations in the soft X-ray band ( keV) with 70-month averaged Swift/BAT data. The nonblazar AGNs of our sample are almost equally divided into unobscured ( ) and obscured ( ) AGNs, and their Swift/BAT continuum is systematically steeper than the 0.3-10 keV emission, which suggests that the presence of a high-energy cutoff is almost ubiquitous. We discuss the main X-ray spectral parameters obtained, such as the photon index, the reflection parameter, the energy of the cutoff, neutral and ionized absorbers, and the soft excess for both obscured and unobscured AGNs.
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