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All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Evidence for Helical Magnetic fields in Kiloparsec-Scale AGN Jets and the Action of a Cosmic Battery

A search for transverse kiloparsec-scale gradients in Faraday rotation-measure (RM) maps of extragalactic radio sources in the literature has yielded 6 AGNs displaying continuous, monotonic RM gradients across their jets, oriented roughly orthogonal to the local jet direction. The most natural interpretation of such transverse RM gradients is that they are caused by the systematic change in the line-of-sight components of helical magnetic fields associated with these jets. All the identified transverse RM gradients increase in the counterclockwise (CCW) direction on the sky relative to the centers of these AGNs. Taken together with the results of Contopoulos et al. who found evidence for a predominance of clockwise (CW) transverse RM gradients across parsec-scale (VLBI) jets, this provides new evidence for preferred orientations of RM gradients due to helical jet magnetic fields, with a reversal from CW in the inner jets to CCW farther from the centers of activity. This can be explained by the "Poynting-Robertson cosmic-battery" mechanism, which can generate helical magnetic fields with a. characteristic "twist," which are expelled with the jet outflows. If the Poynting-Robertson battery mechanism is not operating, an alternative mechanism must be identified, which is able to explain the 'predominance of CW /CCW RM gradients on parsec/kiloparsec scales.

Gabuzda, D. C.↗
NASA NTRS2013

WISE J233237.05-505643.5: A Double-Peaked Broad-Lined AGN with Spiral-Shaped Radio Morphology

We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered double-peaked broad-lined AGN WISE J233237.05-505643.5 at redshift z = 0.3447. This source exhibits an FR-I and FR-II hybrid-morphology, characterized by bright core, jet, and Doppler-boosted lobe structures in ATCA continuum maps at 1.5, 5.6, and 9 GHz. Unlike most FR-II objects, W2332-5056 is hosted by a disk-like galaxy. The core has a projected 5" linear radio feature that is perpendicular to the curved primary jet, hinting at unusual and complex activity within the inner 25 kpc. The multi-epoch optical-near-IR photometric measurements indicate significant variability over a 3-20 year baseline from the AGN component. Gemini-South optical data shows an unusual double-peaked emission-line features: the centroids of the broad-lined components of H-alpha and H-beta are blueshifted with respect to the narrow lines and host galaxy by approximately 3800 km/s. We examine possible cases which involve single or double supermassive black holes in the system, and discuss required future investigations to disentangle the mystery nature of this system.

galaxies: individual↗
NASA NTRS2016

IC 751: A New Changing Look AGN Discovered by NuSTAR

We present results of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the type 2 active galactic nucleus (AGN) in IC 751, three of which were performed simultaneously with XMM-Newton or Swift/ X-Ray Telescope. We find that the nuclear X-ray source underwent a clear transition from a Compton-thick (NH approx. = 2 x10(exp 24)/sq cm) to a Compton-thin ( N(sub H) approx. = 4 x10(exp 23)/sq cm) state on timescales of < or approx.3 months, which makes IC 751 the first changing look AGN discovered by NuSTAR. Changes of the line of sight column density at the approx.2 (sigma) level are also found on a timescale of approx. 48 hr (delta N(sub H approx. 10(exp 23)/sq cm). From the lack of spectral variability on timescales of approx.100 ks, we infer that the varying absorber is located beyond the emission-weighted average radius of the broad-line region (BLR), and could therefore be related either to the external part of the BLR or a clumpy molecular torus. By adopting a physical torus X-ray spectral model, we are able to disentangle the column density of the non-varying absorber (N(sub H) approx. 3.8 x10(exp 23)/sq cm) from that of the varying clouds [N(sub H) approx. (1- 150) x 10(exp 22)/sq cm], and to constrain that of the material responsible for the reprocessed X-ray radiation (N(sub H approx. 6 x 10(exp 24)/sq cm).24 -2). We find evidence of significant intrinsic X-ray variability, with the flux varying by a factor of five on timescales of a few months in the 2-10 and 10-50 keV band.

indivdual: Seyfert↗
NASA NTRS2019

Dissecting the AGN Disk-Jet System with Joint VLBI-Gaia Analysis

We analyze differences in positions of active galactic nuclei (AGNs) between Gaia data release 2 and very long baseline interferometry (VLBI) and compare the significant VLBI-to-Gaia offsets in more than 1000 objects with their jet directions. Remarkably at least three-fourths of the significant offsets are confirmed to occur downstream or upstream of the jet representing a genuine astrophysical effect. Introducing redshift and Gaia color into analysis can help distinguish between the contribution of the host galaxy, jet, and accretion disk emission. We find that strong optical jet emission at least 20-50 pc long is required to explain the Gaia positions located downstream fromVLBI ones. Offsets in the upstream direction of up to 2 mas are at least partly due to the dominant impact of the accretion disk on the Gaia coordinates and by the effects of the parsec-scale radio jet. The host galaxy was found not to play an important role in the detected offsets. BL Lacertae object and Seyfert 2 galaxies are observationally confirmed to have a relatively weak disk and consequently downstream offsets. The disk emission drives upstream offsets in a significant fraction of quasars and Seyfert 1 galaxies when it dominates over the jet in the optical band. The observed behavior of the different AGN classes is consistent with the unified scheme assuming varying contribution of the obscuring dusty torus and jet beaming.

Plavin, A. V.↗
NASA NTRS2019

Warm Absorber Diagnostics of AGN Dynamics

Warm absorbers and related phenomena are some of the observable manifestations of outflows or winds from active galactic nuclei (AGNs). Warm absorbers are common in low-luminosity AGNs. They have been extensively studied observationally and are well described by simple phenomenological models. However, major open questions remain. What is the driving mechanism? What is the density and geometrical distribution? How much associated fully ionized gas is there? What is the relation to the quasi-relativistic "ultrafast outflows"? In this paper we present synthetic spectra for the observable properties of warm absorber flows and associated quantities. We use ab initio dynamical models, i.e., solutions of the equations of motion for gas in finite difference form. The models employ various plausible assumptions for the origin of the warm absorber gas and the physical mechanisms affecting its motion. The synthetic spectra are presented as an observational test of these models. In this way we explore various scenarios for warm absorber dynamics. We show that observed spectra place certain requirements on the geometrical distribution of the warm absorber gas, and that not all dynamical scenarios are equally successful at producing spectra similar to what is observed.

Kallman, Timothy R.↗
NASA NTRS2019

Photoionization Calculations of the Radiation Force Due To Spectral Lines in AGNs

One of the main mechanisms that could drive mass outflows in active galactic nuclei (AGNs) is radiation pressure due to spectral lines. Although straightforward to understand, the actual magnitude of the radiation force is challenging to compute because the force depends on the physical conditions in the gas, as well as the strength, spectral energy distribution (SED), and geometry of the radiation field. We present results from our photoionization and radiation transfer calculations of the force multiplier, M(ξ, t), using the same radiation field to compute the gas photoionization and thermal balance. We assume low gas density (n = 104 per cu.cm) and column density (N ≤ 1017 per sq.cm), a Boltzmann distribution for the level populations, and the Sobolev approximation. Here, we describe results for two SEDs corresponding to an unobscured and obscured AGN in NGC 5548. Our main results are the following: (1) although M(ξ, t) starts to decrease with ξ for ξ gsim 1 as shown by others, this decrease in our calculations is relatively gradual and could be nonmonotonic as M(ξ, t) can increase by a factor of a few for ξ ≈ 10–1000; (2) at these same ξ for which the multiplier is higher than in previous calculations, the gas is thermally unstable by the isobaric criterion; (3) non-local thermodynamic equilibrium effects reduce M(t, ξ) by over two orders of magnitude for ξ gsim 100. The dynamical consequence of result (1) is that line driving can be important for ξ as high as 1000 when the LTE approximation holds, while result (2) provides a natural cloud formation mechanism that may account for the existence of narrow line regions. Result (3) suggests that line driving may not be important for ξ gsim 100 in tenuous plasma.

Dannen, Randall C.↗
NASA NTRS2019

A Dissection of Spatially Resolved AGN Feedback across the Electromagnetic Spectrum

We present optical SuperNova Integral Field Spectrograph integral field spectroscopy, Hubble Space Telescope optical imaging, Chandra X-ray imaging, and Very Large Array radio interferometry of the merging galaxy 2MASX J04234080+0408017, which hosts a Seyfert 2 active galactic nucleus (AGN) at z = 0.046. Our observations reveal that radiatively driven, ionized gas outflows are successful to distances >10 kpc due to the low mass of the host system, encompassing the entirety of the observed optical emission. We also find that at large radii, where observed velocities cannot be reproduced by radiative driving models, high-velocity kinematics are likely due to mechanical driving from AGN winds impacting high-density host material. This impacting deposits sufficient energy to shock the host material, producing thermal X-ray emission and cosmic rays, which in turn promote the formation of in situ radio structure in a pseudo-jet morphology along the high-density lanes.

Travis Fischer↗
NASA NTRS2019

The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey

Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200–350 times in 0.3–10 keV X-ray and six UV/optical bands. Uniform reduction and cross-correlation analysis of these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for the lamp-post reprocessing model in which variations in a central X-ray corona drive and power those in the surrounding accretion disk. (2) The UV/optical interband lags are generally consistent with t μ l4 3 as predicted by the centrally illuminated thin accretion disk model. While the average interband lags are somewhat larger than predicted, these results alone are not inconsistent with the thin disk model given the large systematic uncertainties involved. (3) The one exception is the U band lags, which are on average a factor of ∼2.2 larger than predicted from the surrounding band data and fits. This excess appears to be due to diffuse continuum emission from the broad-line region (BLR). The precise mixing of disk and BLR components cannot be determined from these data alone. The lags in different AGN appear to scale with mass or luminosity. We also find that there are systematic differences between the uncertainties derived by JAVELIN versus more standard lag measurement techniques, with JAVELIN reporting smaller uncertainties by a factor of 2.5 on average. In order to be conservative only standard techniques were used in the analyses reported herein.

R. Edelson↗
NASA NTRSDate not supplied

State of the AGN: Progress Toward Understanding Black Hole Accretion Processes

Accretion of plasma onto black holes power some of the most powerful systems in the cosmos. Supermassive black holes at the centers of galaxies represent the high-mass limit of these objects and so account for the most luminous accretors. As a result, their influence spans vast spatial and temporal scales of cosmic phenomena: intracluster heating, intergalactic media, galactic feedback and star formation, kiloparsec-scale jets/outflows, variability over time scales of minutes to centuries, and luminous multi-wavelength electromagnetic emission extending all the way down to its event horizon. Their intrigue is heightened by the fact that they lie at the intersection of various physical laws---e.g., general relativistic gravity, magnetohydrodynamics, radiation, high-energy particle physics, thermodynamics, and photo-ionization---which all must be reconciled to arrive at a fundamental understanding and probe for new physics, like tests of general relativity. These physics ingredients must be incorporated into simulations performed somehow on dynamical scales ranging from that of the event horizon to parsec-scales. Fortunately, new computational and theoretical techniques---such as GPU computing, radiation transport, and and novel gridding techniques---are enabling progress to larger scales, more degrees of freedom, and even to binary systems. Some of the topics we will survey include recent progress on simulating the relationship between the disk-jet interaction, how tilted black holes behave, radiation-dominated flow, and how binary AGN affect the standard picture of black hole accretion. Along the way, we will highlight how new technologies have enabled these scientific rewards. Future directions and open questions will be provided to inspire discussion and interaction during the session.

LISA↗
NASA NTRS1984

A universal spectrum for AGNs and QSOs

The effects of the feedback of e+-e- pair reinjection in a plasma due to photon photon absorption of its own radiation is examined. Under the assumption of continuous electron injection with a power law spectrum and Compton losses only, it is shown that for power law index 2 the steady state electron distribution function has a unique form independent of the primary injection spectrum. This electron distribution function can by then reproduce the general characteristics of AGN, QSO spectra from radio to X-rays. It also implies gamma ray emission from these objects consistent with the observations of the diffuse gamma ray background.

Kazanas, D.↗
NASA NTRS1987

IRAS observations of AGN candidates at low flux levels

IRAS additional observations were used to obtain a sample of point sources at much fainter flux levels than hitherto available through the IRAS Point Source Catalogue. This sample is being used to compile an incomplete but representative catalogue of faint IRAS candidate Active Galactic Nuclei (AGNs) and to study the evolution of the infrared bright galaxies. Ground based follow up observations (optical spectroscopy) are mainly hampered by identification confusion.

Degrijp, Marinus H. K.↗
NASA NTRS1987

Constraints on possible precursor AGN sources of the cosmic X-ray background

New limits on small-scale surface brightness fluctuations of the residual cosmic X-ray background are used to reevaluate the conjecture that unresolved precursor AGN sources could be the origin of the flux. The large number of these predominantly X-ray-emitting objects thereby required imposes that their lifetime be longer than previously considered. Attention is drawn to the fact that the reduction in the effective Eddington luminosity limit for such sources due to electron-positron pair opacity could have the effect of increasing their lifetime to an appropriate level.

Boldt, Elihu↗
NASA NTRS1988

Induced stellar mass loss in AGN's

The effect of star-gas drag on stellar dynamics and stellar mass loss in active nuclei is discussed. It is assumed that red giants are much too rare in AGNs and that the stellar population consists mainly of late-type main-sequence stars. It is found that the star-gas drag is often the dominant mechanism triggering the mass loss from these stars at rates up to 100,000 times the usual rate for the main-sequence star. It is shown that the gas and radiation will impose a substantial turbulent stripping of or a Compton drag on the outer layers of stars.

Shlosman, Isaac↗
NASA NTRS1988

The central engine of quasars and AGN's - Shock-accelerated relativistic protons

A simple dynamical model is presented in which protons are Fermi-shock-accelerated to relativistic energies and do not readily fall into the black hole. It is shown that, even though the nonthermal radiation from QSOs and AGNs is generally well below the Eddington limit, it is still highly correlated and proportional to the mass. In the present model, the proportionality constant is determined by the p-p cross-section and the minimum shock radius (in units of the Schwarzschild radius) where a stable shock is assumed to exist. The model predicts a rapid drop off in efficiency as this shock radius increases.

Ellison, Donald C.↗
NASA NTRS1988

The central engine of quasars and AGNs - Scaling to solar mass black holes

The model of the previous paper (Ellison and Kazanas, hereafter EK) can be readily scaled to model systems with black holes 3-10 solar masses, such as those expected to exist in certain Galactic X-ray binaries. The model can account in a straightforward way for the bimodal behavior of Cyg X-1 and the other Galactic black hole candidates (White and Marshall 1984; White, et al., 1984). It is argued that the change in the spectrum with luminosity is due to the drastic increase of both the source compactness and luminosity with small changes in the accretion rate, and conversion of most of the energy into electron-positron pairs which render the source optically thick and modify its spectrum. It is also argued that similar effects may be observed in AGNs.

Kazanas, D.↗
NASA NTRS1989

Accurate galactic N(H) values towards quasars and AGN

Integrated Galactic 21-cm column densities toward about 174 quasars and AGN are presented. The data are corrected for stray radiation, using the technique of Lockman et al. (1986). Because of the 21-arcmin beam size of the 140-ft telescope used in the study, the uncertainty in N(H) due to angular variations in the H I of the Galaxy at high latitudes is minimized. The column densities are accurate to about 1 X 10 to the 19th atoms/sq cm, or 5 percent, whichever is larger. Errors above N(H) of about 4 X 10 to the 20th atoms/sq cm are dominated by opacity uncertainties.

Elvis, Martin↗
NASA NTRS1989

The complex X ray spectra of AGN

X-ray spectral surveys of large samples of Seyfert galaxies are discussed. The spectral shape in the 0.1 to 20 keV energy range is considered. Two new spectral survey are undertaken, one involving 105 Imaging Proportional Counter (IPC) observations of 75 Seyfert galaxies, the other using IPC and Monitor Proportional Counter (MPC) data from 28 observations of 23 Seyfert galaxies. The X-ray spectra of active galactic nuclei (AGN) are complex, with in most cases considerable steepening at the lowest energies. At higher energies (2 to 20 keV), the existence of a universal, canonical power law is confirmed, independent of X-ray luminosity over four orders of magnitude.

Urry, C. M.↗
NASA NTRS1989

X ray emission from relativistic jets in AGNs and statistical implications

Calculations of the Compton scattering interaction between an ultrarelativistic jet and a thermal radiation field, in an Active Galactic Nuclei (AGN), are presented. This process can be effective in decelerating ultrarelativistic jets that are accelerated by electromagnetic or hydromagnetic forces closer in to the central black hole. A narrow distribution of terminal Lorentz factors gamma sub infinity, consistent with the values inferred in superluminal radio sources, arises naturally in this model. The hard X-ray component detected in the spectra of 3C273 and several BL Lac objects may be due to the inverse Compton radiation produced in the course of the initial deceleration of their relativistic jets. The requirement that the luminosity of the hard X-ray component must exceed the total power in the associated jet is considered.

Melia, Fulvio↗