Search NASA⌕ Search

SEARCH · Search NASA

Results for “3C”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

Radioastron Discovery of A Mini-Cocoon Around the Restarted Parsec-Scale Jet in 3C 84

We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C 84 (NGC 1275) at the centre of the Perseus cluster. The observations were carried out during a perigee passage of the Spektr-R spacecraft on September 21–22, 2013 and involved a global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz, together with the Space Radio Telescope (SRT). Furthermore, the Very Long Baseline Array (VLBA) and the phased Very Large Array (VLA) observed the source quasi-simultaneously at 15 GHz and 43 GHz. Fringes between the ground array and the SRT were detected on baseline lengths up to 8.1 times the Earth’s diameter, providing unprecedented resolution for 3C 84 at these wavelengths. We note that the corresponding fringe spacing is 125 μas at 5 GHz and 27 μas at 22 GHz. Our space-VLBI images reveal a previously unseen sub-structure inside the compact ∼1 pc long jet that was ejected about ten years earlier. In the 5 GHz image, we detected, for the first time, low-intensity emission from a cocoon-like structure around the restarted jet. Our results suggest that the increased power of the young jet is inflating a bubble of hot plasma as it carves its way through the ambient medium of the central region of the galaxy. Here, we estimate the minimum energy stored in the mini-cocoon, along with its pressure, volume, expansion speed, and the ratio of heavy particles to relativistic electrons, as well as the density of the ambient medium. About half of the energy delivered by the jet is dumped into the mini-cocoon and the quasi-spherical shape of the bubble suggests that this energy may be transferred to a significantly larger volume of the interstellar medium than what would be accomplished by the well-collimated jet on its own. The pressure of the hot mini-cocoon also provides a natural explanation for the almost cylindrical jet profile seen in the 22 GHz RadioAstron image.

galaxies: jets↗
DOE OSTI2021

Theoretical study of intrinsic defects in cubic silicon carbide 3C-SiC

Using the local moment counter charge (LMCC) method to accurately represent the asymptotic electrostatic boundary conditions within density functional theory supercell calculations, we present a comprehensive analysis of the atomic structure and energy levels of point defects in cubic silicon carbide (3C-SiC). Finding that the classical long-range dielectric screening outside the supercell induced by a charged defect is a significant contributor to the total energy. we describe and validate a modified Jost screening model to evaluate this polarization energy. This leads to bulk-converged defect levels in finite size supercells. With the LMCC boundary conditions and a standard Perdew-Burke-Ernzerhof (PBE) exchange correlation functional, the computed defect level spectrum exhibits no band gap problem: the range of defect levels spans ~2.4 eV, an effective defect band gap that agrees with the experimental band gap. Comparing with previous literature, our LMCC-PBE defect results are in consistent agreement with the hybrid-exchange functional results of Oda et al. [J. Chem. Phys. 139, 124707 (2013)] rather than their PBE results. The difference with their PBE results is attributed to their use of a conventional jellium approximation rather than the more rigorous LMCC approach for handling charged supercell boundary conditions. The difference between standard dft and hybrid functional results for defect levels lies not in a band gap problem but rather in solving a boundary condition problem. The LMCC-PBE entirely mitigates the effect of the band gap problem on defect levels. The more computationally economical PBE enables a systematic exploration of 3C-SiC defects, where, most notably, we find that the silicon vacancy undergoes Jahn-Teller-induced distortions from the previously assumed T d symmetry, and that the divacancy, like the silicon vacancy, exhibits a site-shift bistability in p -type conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

High-Q suspended optical resonators in 3C silicon carbide obtained by thermal annealing

We fabricate suspended single-mode optical waveguides and ring resonators in 3C silicon carbide (SiC) that operate at telecommunication wavelength, and leverage post-fabrication thermal annealing to minimize optical propagation losses. Annealed optical resonators yield quality factors of over 41,000, which corresponds to a propagation loss of 7 dB/cm, and is a significant improvement over the 24 dB/cm in the case of the non-annealed chip. This improvement is attributed to the enhancement of SiC crystallinity and a significant reduction of waveguide surface roughness, from 2.4 nm to below 1.7 nm. The latter is attributed to surface layer oxide growth during the annealing step. We confirm that the thermo-optic coefficient, an important parameter governing high-power and temperature-dependent performance of SiC, does not vary with annealing and is comparable to that of bulk SiC. Our annealing-based approach, which is especially suitable for suspended structures, offers a straightforward way to realize high-performance 3C-SiC integrated circuits.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Dust Reverberation of 3C 273: Torus Structure and Lag–Luminosity Relation

We monitored the z = 0.158 quasar 3C 273 between 2015 and 2019 in the optical (BVrz) and near-infrared (JHK) with the aim to perform dust reverberation mapping. Accounting for host galaxy and accretion disk contributions, we obtained pure dust light curves in JHK. Cross correlations between the V band and the dust light curves yield an average rest-frame delay for the hot dust of τ {sub cent} ∼ 410 days. This is a factor of two shorter than that expected from the the dust ring radius R {sub x} ∼ 900 lt-day reported from interferometric studies. The dust covering factor (CF) is about 8%, much smaller than that predicted from the half covering angle of 45° found for active galactic nuclei (AGNs). We analyze the asymmetric shape of the correlation functions and explore whether an inclined biconical bowl-shaped dust torus geometry could bring these findings (τ {sub cent}, R {sub x} and CF) into a consistent picture. The hot varying dust emission originates from the edge of the bowl rim with a small covering angle 40° < θ < 45°, and we see only the near side of the biconus. Such a dust gloriole with R {sub x} = 900 ± 200 lt-day and an inclination 12° matches the data remarkably well. Comparing the results of 3C 273 with literature for less luminous AGN, we find a lag–luminosity relation τ ∝ L {sup α} with α = 0.33–0.40, flatter than the widely adopted relation with α ∼ 0.5. We address several explanations for the new lag–luminosity relation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Revisiting the Supernova Engines in the 3C 397 and W49B Supernova Remnants

The nature of the supernova remnants (SNRs) 3C 397 and W49B has long been a subject of debate, with prior studies offering conflicting interpretations between thermonuclear and core-collapse scenarios. To help settle this debate, we present a systematic, spatially resolved, spectroscopic analysis of both remnants using XMM-Newton. By applying multicomponent thermal models, we derive key physical properties including elemental abundances, ejecta temperatures, ambient densities, and explosion energetics. We compare the inferred metal abundance ratios to a wide range of core-collapse and thermonuclear nucleosynthesis models, including new models whose explosion energies differ from the canonical value of 10 51 erg. We find that the observed Fe/Si and Ca/Si ratios in both SNRs are best matched by certain thermonuclear models. However, no model fully reproduces the complete set of observed abundance patterns. In 3C 397, high Fe enrichment and spatial abundance variations suggest interaction with a dense progenitor environment, and W49B’s composition is overall consistent with a thermonuclear origin; however, both require a low-energy (∼10 50 erg) supernova explosion. We additionally map the Fe Kα line centroid energies and find a spread, with W49B falling within the core-collapse region—highlighting both environmental complexity and the limitations of this diagnostic for supernova classification. Our results highlight the need for caution in relying on any single diagnostic or nucleosynthesis model for supernova typing, underscore the need for improved nucleosynthesis models, and motivate future high-resolution, high-throughput observations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Limits on intergalactic helium from the 3C 273 X-ray spectrum

An X-ray spectrum of the quasi-stellar object 3C 273 in the interval 0.25 to 10 KeV was obtained by sounding rocket observations. The best-fit power law spectrum has photon index n= 1.3 with no photoelectric absorption. An upper limit on the X-ray optical depth to 3C 273 was calculated from the data, permitting upper limits to be set on the absolute abundance of helium in the intergalactic medium.

Margon, B.↗
NASA NTRS1972

The optical object identified with 3C 455.

It is shown that the optical object identified with 3C 455 is a quasi-stellar object with a redshift z = 0.543. The QSO is situated 23 sec northeast of the S0 galaxy NGC 7413, which has a redshift of 0.0332. It is pointed out that the discovery of the present object in a position so close to a galaxy is further evidence in favor of the existence of a physical association between 3C QSOs and bright galaxies.

Arp, H. C.↗
NASA NTRS1972

NGC 1068, 3C 273, and Scorpius X-1 - Circular polarization disputed.

Discussion of data for the Seyfert galaxy NGC 1068, the quasar 3C 273, and the X-ray source Sco X-1, for all of which it has been claimed or strongly suggested that they have large circular polarization of the order of 1% (Severny et al., 1971). In contrast the present authors obtained unambiguously null results with upper limits about 0.05% for NGC 1068 and 3C 273. For Sco X-1 no statistically significant polarization was found on three nights, and only some marginal evidence for a fluctuation or transient polarization on one night.

Kemp, J. C.↗
NASA NTRS1972

Limits on intergalactic helium from the 3C 273 X-ray spectrum.

An X-ray spectrum of the quasi-stellar object 3C 273 in the interval 0.25-10 keV has been obtained by sounding-rocket observations. The best-fit power-law spectrum has a photon index n = 1.3 with no photoelectric absorption. An upper limit on the X-ray optical depth to 3C 273 has been calculated from the data, permitting upper limits to be set on the absolute abundance of helium in the intergalactic medium.

Margon, B.↗
NASA NTRS1976

Time-dependent radio fine structure of the quasar 3C 345

Results are reported for VLBI observations of 3C 345 at a wavelength of 3.8 cm with left circular polarization. Sixteen sets of correlated flux densities and three sets of closure phases were obtained from observations made over a three-year period with six independent interferometers formed from up to four antennas. The mathematical models employed to represent the radio brightness distribution of the source are described, and the data are analyzed on the basis of a two-component model. The results show that the compact source in 3C 345 consists of two components whose separation increased by about 0.3 milliarcsec over the observational period, that the smaller and weaker component is to the east and south of the larger and stronger one, and that the apparent expansion velocity would be about 2.5c for a redshift of 0.6, a Hubble constant of 60 km/sec per Mpc, and a deceleration parameter of unity. It is concluded that these findings are difficult to reconcile with the 'Christmas tree' model for the apparent change of separation with time over any given series of observations.

Wittels, J. J.↗
NASA NTRS1979

3C 273 - X-ray variability, spectrum, and position

Observations of the X-ray source associated with 3C 273 have been carried out from 1.3 to 13.3 keV with the scanning modulation collimator on HEAO 1, yielding several precise positions (0.42 sq arcmin), one of which includes 3C 273. The data show an increase in flux by a factor of at least 3 in 6 months. A substantial low-energy (1.3-2.6 keV) flux during the higher state yields a hydrogen column density of less than 2 x 10 to the 22nd per sq cm and removes a possible X-ray distinction between quasars and other extragalactic nuclei, viz., Seyfert type 1 and BL Lacertae objects. The 90-GHz radio flux decreased during this period (1978.0-1978.5), and the optical flux exhibited increased variability after several years of relative quiescence.

Bradt, H. V.↗
NASA NTRS1979

IUE observations of the quasar 3C 273

IUE observations indicate that the spectrum of 3C 273 is similar to that of other large-redshift quasars. There is a large excess of flux in the range 2400 A to 5300 A, which encompasses the Balmer jump region but which does not appear to be explainable by Balmer emission. The intensity ratio of Lyman-alpha to H-beta is 5.5, in agreement with other measures and a factor 6 smaller than the recombination value. The only absorption lines in the spectrum are due to our Galaxy. There is marginal evidence for a depression of the continuum shortward of the Lyman-alpha emission line, but the errors are too large to warrant any conclusion that 3C 273 has a rich absorption-line spectrum such as that seen in large-redshift quasars. The absence of emission and absorption lines of Fe II leads to the conclusion that resonance fluorescence probably produces the visual Fe II emission lines.

Boggess, A.↗
NASA NTRS1979

IUE and visual spectrophotometry of 3C 120 and Markarian 79

Low-resolution ultraviolet spectra have been obtained with IUE and combined with similar visual observations. The continua of both objects show an excess of flux in the neighborhood of 3000 A. In both objects there appears to be a depression near 2200 A, which is probably the ultraviolet interstellar absorption feature centered at 2175 A. The strength of this feature suggests E(B-V) values of 0.22 and 0.38 for Mrk 79 and 3C 120, respectively. The ratio of intensities of L-alpha to H-beta is abnormally small compared with the radiative recombination ratio; the discrepancy is removed in 3C 120 and much reduced in Mrk 79 if the reddening values just mentioned are adopted. The C IV to L-alpha line intensity ratio is abnormally high in these objects compared with that for quasars. Although both objects have strong Fe II lines in the visual, there is no Fe II absorption or emission in the ultraviolet.

Oke, J. B.↗
NASA NTRS1981

IUE and visual spectrophotometry of Markarian 9, Markarian 10, and 3C 390.3

Ultraviolet spectra from IUE are combined with visual spectra for the three type I Seyfert galaxies Mrk 9, Mrk 10, and 3C 390.3. The 2175 A interstellar feature is measured well enough in Mrk 9 to indicate that the extinction corresponding to E(B-V) = 0.14 + or - 0.04 is in the galaxy. Mrk 10 displays evidence for 2175 A absorption and also yields E(B-V) = 0.14 + or - 0.07, while the continuum for 3C 390.3 is too weak to positively detect the feature. It is found, after correcting for reddening, that the line-intensity ratio L(alpha)/H(beta) ranges from 8 to 18, while that for H(alpha)/H(beta) goes from 2.1 to 5.4. It is noted that the He II 1640/4686 line ratio is uncertain but appears to be consistent with the recombination value of about 8. If photoionization is assumed, a comparison of the strengths of L(alpha) and H(beta) with the UV ionizing flux suggests that H(beta) is enhanced rather than L(alpha) depressed. When a comparison is made with similar ratios in quasars, L(alpha) is found to be much stronger and H(beta) slightly stronger in Seyferts than in quasars.

Oke, J. B.↗
NASA NTRS1981

Galactic disk absorption lines in the spectrum of the quasar 3C 273

It is pointed out that the line of sight to 3C 273 is unique because of the possibility of obtaining both radio and optical absorption line measurements. This information may make it possible to understand in detail the structure of the interstellar medium along the line of sight. To take advantage of this possibility, high-resolution optical spectra were obtained of 3C 273. The observations were made using the echelle spectrograph at the Cassegrain focus of the 4 m telescope at the Cerro Tololo Inter-American Observatory in 1980 January. Both Na D and Ca K lines were obtained on the same plate. In the visual lines, the galactic disk absorption shows a main component at 20 km/sec with a trailing wing in the negative velocities.

Cowie, L. L.↗
NASA NTRS1982

An X-ray study of two Crablike supernova remnants - 3C 58 and CTB 80

The instruments on the Einstein Observatory have been used to study the X-ray properties of two Crablike SNRs: 3C 58 and CTB 80. Images of the objects are similar, showing an extended plateau of emission surrounding a pronounced central maximum consistent with the presence of a point source. The X-ray spectrum of 3C 58 is consistent with a power law of spectral index 0.5 + 0.5 or -0.2 modified by absorption in a hydrogen column density N sub H of (2 + or - 0.5) x 10 to the 21st/sq cm. These data suggest an analogy with the Crab Nebula, where the extended X-ray emission is nonthermal and the pointlike emission emanates from a central neutron star. Quantitative comparisons of the X-ray and radio properties for six Crablike remnants indicate significant differences which may reflect an evolutionary sequence.

Becker, R. H.↗
NASA NTRS1983

The peculiar radio galaxy 3C 433

Radio, optical and X-ray observations are presented of the peculiar radio galaxy 3C 433, a Seyfert 2 object with luminosity an order of magnitude greater than that expected from its complex, shell-type morphology. Observations conducted at 6 and 12 cm with the VLA and at 21 cm with the Westerbork telescope show a striking asymmetry between the northern and southern radio emissions, and an overall X-shaped morphology. Optical observations using the Video Camera and High Gain Video Spectrometer on the 4-m telescope and the Intensified Image Dissector Scanner on the 2.1-m telescope at Kitt Peak confirm the identification of the source with a pair of bright galaxies. Observations in the X-ray from the Einstein Observatory IPC reveal an unresolved source at the position of 3C 433, as well as two serendipitous X-ray sources. The observations may be used to explain the overall structure of the source either in terms of tidal torquing or precessing models of double galaxies; however, it is argued that the tidal torquing model requires fewer assumptions to account for the brightness asymmetry.

Van Breugel, W.↗