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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Chandra Reveals Heavy Obscuration and Circumnuclear Star Formation in Seyfert 2 Galaxy NGC 4968

We present the Chandra imaging and spectral analysis of NGC 4968, a nearby (z = 0.00986) Seyfert 2 galaxy. We discover extended (approx. 1 kpc) X-ray emission in the soft band (0.5-2 keV) that is neither coincident with the narrow line region nor the extended radio emission. Based on spectral modeling, it is linked to on-going star formation [approx. 2.6-4 Mass compared to Earth yr(exp.− 1)]. The soft emission at circumnuclear scales (inner approx. 400 pc) originates from hot gas, with kT approx. 0.7 keV, while the most extended thermal emission is cooler (kT approx. 0.3 keV). We refine previous measurements of the extreme Fe K alpha equivalent width in this source (EW 2.5 + 2.6/-1.0 keV), which suggests the central engine is completely embedded within Compton-thick levels of obscuration. Using physically motivated models fit to the Chandra spectrum, we derive a Compton-thick column density [N(sub H) is greater than 1.25× 10(exp 24) cm(exp.− 2)] and an intrinsic hard (2-10 keV) X-ray luminosity of approx. 3-8× 10(exp. 42) erg s(exp. − 1) (depending on the presumed geometry of the obscurer), which is over two orders of magnitude larger than that observed. The large Fe K Alpha EW suggests a spherical covering geometry, which could be confirmed with X-ray measurements above 10 keV. NGC 4968 is similar to other active galaxies that exhibit extreme Fe K Alpha EWs (i.e., greater than 2 keV) in that they also contain on-going star formation. This work supports the idea that gas associated with nuclear star formation may increase the covering factor of the enshrouding gas and play a role in obscuring active galactic nuclei.

LaMassa, Stephanie M.↗
NASA NTRS2018

Optical Polarisation Variability of Radio-Loud Narrow-Line Seyfert 1 Galaxies: Search for Long Rotations of the Polarisation Plane

This work describes multi-site optical polarimetric observations of several radio-loud Narrow Line Seyfert 1 galaxies. This source class, and the sources in this study, were discovered to be detectable at gamma-ray energies by the Large Area Telescope (LAT) aboard the Fermi satellite. GSFC has played a key role in the development, launch, and operation of Fermi/LAT.

Angelakis, E.↗
NASA NTRS2019

Spatially Resolved Outflows in a Seyfert Galaxy at z=2.39

We present the first spatially resolved analysis of rest-frame optical and UV (UltraViolet) imaging and spectroscopy for a lensed galaxy at z equals 2.39 hosting a Seyfert active galactic nucleus (AGN). Proximity to a natural guide star has enabled observations with high signal-to-noise ratio using Very Large Telescope SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) plus adaptive optics (AO) of rest-frame optical diagnostic emission lines, which exhibit an underlying broad component with full width at half maximum approximately 700 kilometers per second in both the Balmer and forbidden lines. Measured line ratios place the outflow robustly in the region of the ionization diagnostic diagrams associated with AGNs. This unique opportunity - combining gravitational lensing, AO guiding, redshift, and AGN activity - allows for a magnified view of two main tracers of the physical conditions and structure of the interstellar medium in a star-forming galaxy hosting a weak AGN at Cosmic Noon. By analyzing the spatial extent and morphology of the Lyman alpha spectral line and dust-corrected Hydrogen spectral line emission, disentangling the effects of star formation and AGN ionization on each tracer, and comparing the AGN-induced mass outflow rate to the host star formation rate, we find that the AGN does not significantly impact the star formation within its host galaxy.

Fischer, Travis C.↗
NASA NTRS2020

An Obscured, Seyfert 2-like State of the Stellar-mass Black Hole GRS 1915+105 Caused by Failed Disk Winds

We report on Chandra grating spectra of the stellar-mass black hole GRS 1915+105 obtained during a novel, highly obscured state. As the source entered this state, a dense, massive accretion disk wind was detected through strong absorption lines. Photoionization modeling indicates that it must originate close to the central engine, orders of magnitude from the outer accretion disk. Strong, nearly sinusoidal flux variability in this phase yielded a key insight: the wind is blueshifted when its column density is relatively low, but redshifted as it approaches the Compton-thick threshold. At no point does the wind appear to achieve the local escape velocity; in this sense, it is a “failed wind.” Later observations suggest that the disk ultimately fails to keep even the central engine clear of gas, leading to heavily obscured and Compton-thick states characterized by very strong Fe K emission lines. Indeed, these later spectra are successfully described using models developed for obscured active galactic nuclei (AGNs). We discuss our results in terms of the remarkable similarity of GRS 1915+105 deep in its “obscured state” to Seyfert 2 and Compton-thick AGNs, and we explore how our understanding of accretion and obscuration in massive black holes is impacted by our observations.

Black holes↗
NASA NTRS2021

A Weakening Compton Hump and Soft X-ray Excess Detected in the Seyfert-1 Galaxy MCG –02–58–22

We have carried out an extensive X-ray spectral study of the bare Seyfert-1 galaxy MCG –02–58–22to ascertain the nature of the X-ray reprocessing media, using observations from Suzaku(2009) and simultaneous observations from XMM-Newton and NuSTAR(2016) . The most significant results of our investigation are: 1. The primary X-ray emission from the corona is constant in these observations, both in terms of the power law slope (Γ = 1.80) and luminosity (L2−10 keV= 2.55×1044erg s−1). 2.The soft excess flux decreased by a factor of two in 2016, the Compton hump weakened/vanished in2016, and the narrow FeKαemission line became marginally broad (σ= 0.35±0.08 keV) and its flux doubled in 2016. 3. From physical model fits we find that the normalization of the narrow component of the FeKαline does not change in the two epochs, although the Compton hump vanishes in the same time span. Since the primary X-ray continuum does not change, we presume that any changes in there processed emission must arise due to changes in the reprocessing media. Our primary conclusions are: A. The vanishing of the Compton hump in 2016 can probably be explained by a dynamic clumpytorus which is infalling/outflowing, or by a polar torus wind. B. The torus in this AGN possibly has two structures: an equatorial toroidal disk (producing the narrow FeKαemission) and a polar component(producing the variable Compton hump), C. The reduction of the soft-excess flux by half and increase in the FeKαflux by a factor of two in the same period cannot be adequately explained by ionized disk reflection model alone.

Sibasish Laha↗
NASA NTRS2022

Polarization Constraints on the X-ray Corona in Seyfert Galaxies: MCG-05-23-16

We report on the first observation of a radio-quiet Active Galactic Nucleus (AGN) inpolarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source was pointed at with theImaging X-ray Polarimetry Explorer(IXPE) starting on May 14, 2022 for a net observing timeof 486 ks, simultaneously with XMM-Newton(58 ks) andNuSTAR(83 ks). A polarizationdegreeΠsmaller than 4.7% (at the 99% confidence level) is derived in the 2–8 keV energyrange, where emission is dominated by the primary component ascribed to the hot corona.The broad-band spectrum, inferred from a simultaneous fit to theIXPE,NuSTAR, and XMM-Newtondata, is well reproduced by a power law with photon indexΓ=1.85±0.01and ahigh-energy cutoffEC=120±15keV. A comparison with Monte Carlo simulations showsthat a lamp-post and a conical geometry of the corona are consistent with the observed upperlimit, a slab geometry is allowed only if the inclination angle of the system is less than 50◦

A Marinucci↗
NASA NTRS2020

A Broad-Band X-Ray Spectral Study of the Seyfert 1 Galaxy ESO 141–G055 with XMM-Newton and NuSTAR

We have extensively studied the broad–band X-ray spectra of the source ESO 141–G055 using all available XMM–Newton and NuSTAR observations. We detect a prominent soft excess below 2 keV, a narrow Fe line, and a Compton hump (> 10 keV). The origin of the soft excess is still debated. We used two models to describe the soft excess: the blurred reflection from the ionized accretion disc and the intrinsic thermal Comptonization model. We find that both of these models explain the soft excess equally well. We confirm that we do not detect any broad Fe line in the X-ray spectra of this source, although both the physical models prefer a maximally spinning black hole scenario (a > 0.96). This may mean that either the broad Fe line is absent or blurred beyond detection. The Eddington rate of the source is estimated to be λ(sub Edd) ∼ 0.31. In the reflection model, the Compton hump has a contribution from both ionized and neutral reflection components. The neutral reflector which simultaneously describes the narrow Fe K(sub α) and the Compton hump has a column density of N(sub H) ≤ 7 × 10(exp 24) cm(exp -2). In addition, we detect a partially covering ionized absorption with ionization parameter log ξ/ erg cm s(exp -1) = 0.1(sup +0.1)(sub -0.1) and column density N(sub H) = 20.6(sup +1.0)(sub -1.0) × 10(exp 22) cm(exp -2) with a covering factor of 0.21(sup +0.01)(sub -0.01).

ESO 141–G055↗
NASA NTRS2021

Quantifying Feedback from Narrow Line Region Outflows in Nearby Active Galaxies. III. Results for the Seyfert 2 Galaxies Markarian 3, Markarian 78, and NGC 1068

Outflows of ionized gas driven by active galactic nuclei (AGN) may significantly impact the evolution of their host galaxies. However, determining the energetics of these outflows is difficult with spatially unresolved observations that are subject to strong global selection effects. We present part of an ongoing study using Hubble Space Telescope and Apache Point Observatory spectroscopy and imaging to derive spatially resolved mass outflow rates and energetics for narrow-line region outflows in nearby AGN that are based on multi-component photoionization models to account for spatial variations in gas ionization, density, abundances, and dust content. This expanded analysis adds Mrk 3, Mrk 78, and NGC 1068, doubling our earlier sample. We find that the outflows contain total ionized gas masses of M ≈ 10(exp 5.5)-10(exp 7.5) M⨀ and reach peak velocities of v ≈ 800-2000 km s(exp -1). The outflows reach maximum mass outflow rates of M(sub OUT) ≈ 3-12 M⨀ yr(exp -1) and encompass total kinetic energies of E ≈ 10(exp 54)-10(exp 56) erg. The outflows extend to radial distances of r ≈ 0.1-3 kpc from the nucleus, with the gas masses, outflow energetics, and radial extents positively correlated with AGN luminosity. The outflow rates are consistent with in situ ionization and acceleration where gas is radiatively driven at multiple radii. These radial variations indicate that spatially resolved observations are essential for localizing AGN feedback and determining the most accurate outflow parameters.

Active galaxies↗
DOE OSTI2020

NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei. II. Median High-energy Cutoff in Seyfert II Hard X-Ray Spectra

Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGNs) can provide important insights into the physical conditions very close to their central supermassive black holes. The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. In this paper we present a large collection of coronal cutoff constraints for obscured AGNs based on a sample of 130 AGNs selected in the hard X-ray band with Swift/BAT and observed nearly simultaneously with NuSTAR and Swift/XRT. Additionally, we find that under a reasonable set of assumptions regarding partial constraints the median cutoff is well constrained to 290 ± 20 keV, where the uncertainty is statistical and given at the 68% confidence level. We investigate the sensitivity of this result to our assumptions and find that consideration of various known systematic uncertainties robustly places the median cutoff between 240 and 340 keV. The central 68% of the intrinsic cutoff distribution is found to be between about 140 and 500 keV, with estimated uncertainties of 20 and 100 keV, respectively. In comparison with the literature, we find no clear evidence that the cutoffs in obscured and unobscured AGNs are substantially different. Our analysis highlights the importance of carefully considering partial and potentially degenerate constraints on the coronal high-energy cutoff in AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗