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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

High-resolution X-ray observations of M87 - Nucleus, jet and radio halo

X-ray observations of M87 made using the Einstein Observatory HRI show the presence of four components. A broad, diffuse component associated with hot gas in the galaxy follows an approximate inverse power law; the pressure of the gas could be sufficient to confine the inner and outer radio lobes. A diffuse, asymmetrical X-ray distribution to the east and southwest appears similar to the radio morphology and is consistent with an inverse Compton model. An X-ray source centered on the nucleus of the galaxy is extended by 2-3 arcsec and may be due to thermal bremsstrahlung; a possible compact source of less than 10 to the 41st ergs/sec is weak compared with other active galaxies, and its implications for the presence of a massive black hole are discussed. A structure correlated with the radio-optical jet is also seen; the X-ray flux is consistent with an extrapolation of the optical synchrotron spectrum. The four components suggest that all three canonical astrophysical X-ray emission mechanisms are present in M87: thermal bremsstrahlung, inverse Compton scattering, and synchrotron radiation.

Schreier, E. J.↗
NASA NTRS2008

Chandra Confirmation of a Pulsar Wind Nebula in DA 495

As part of a multiwavelength study of the unusual radio supernova remnant DA 495, we present observations made with the Chandra X-ray Observatory. Imaging and spectroscopic analysis confirms the previously detected X-ray source at the heart of the annular radio nebula, establishing the radiative properties of two key emission components: a soft unresolved source with a blackbody temperature of 1 MK consistent with a neutron star, surrounded by a nontherma1 nebula 40" in diameter exhibiting a power-law spectrum with photon index Gamma = 1.63, typical of a pulsar wind nebula. Morphologically, the nebula appears to be slightly extended along a direction, in projection on the sky, previously demonstrated to be of significance in radio and ASCA observations; we argue that this represents the orientation of the pulsar spin axis. At smaller scales, a narrow X-ray feature is seen extending out 5" from the point source, but energetic arguments suggest that it is not the resolved termination shock of the pulsar wind against the ambient medium. Finally, we argue based on synchrotron lifetimes in the nebular magnetic field that DA 495 represents the first example of a pulsar wind nebula in which electromagnetic flux makes up a significant part, together with particle flux, of the neutron star's wind.

Arzoumanian, Z.↗
NASA NTRS2004

Imaging Spectrophotometry of the Jet/ISM Interaction in IC5063

IC5063 is a somewhat dusty z=0.0110 S0 galaxy with a Seyfert 2 nucleus. It has a triple radio source that spans 3 arcsec, mostly blueshifted H I absorption that spans 700 km/s, and ionization cones that extend for more than 2 arcmins. We obtained fully sampled [O III]\lambda5007 grids at 0."9 and 70 km/s FWHM resolution using the Rutgers Fabry-Perot system on the Blanco 4m telescope. Complementary long-slit spectra using the RC spectrograph on the Blanco, and Taurus Tunable Filter spectral images in H\alpha and [N II]\lambda6583, were also obtained to assess gaseous ionization conditions. We present the results of our analysis, and correlate spectral structures to those visible in archival WFPC2 images. We find that, in the region near the radio triple, gaseous ionization and line velocity width is tightly correlated, in excellent quantitative agreement with the high-velocity shock regime in the diagnostic emission-line ratio diagrams of Dopita & Sutherland. We separate kinematically gas in normal disk rotation that is illuminated by the AGN in the ionization cones from that agitated mechanically by the jet, and assess the energy input from both processes.

Cecil, G.↗
NASA NTRS2003

Confirmation of a radio-selected galaxy overdensity at z = 1.11¹

We report the discovery of a galaxy overdensity at z = 1.11 associated with the z = 1.110 high-redshift radio galaxy MG1 J04426+0202 (hereafterMG0442+0202). The group, Cl 0442+0202, was found in a near-infrared survey of z > 1 radio galaxies undertaken to identify spatially coincident regions with a high density of objects red in I-K' color, typical of z > 1 elliptical galaxies. Spectroscopic observations from the Keck I telescope reveal five galaxies within 3500 of MG 0442+0202 at 1.10 < z < 1.11. These member galaxies have broadband colors and optical spectra consistent with passively evolving elliptical galaxies formed at high redshift. Archival ROSAT observations reveal a 3 detection of soft X-ray emission coincident with Cl 0442+0202 at a level 5 times greater than expected for the radio galaxy. These data suggest a rich galaxy cluster and inspired a 45 ks Chandra X-Ray Observatory observation. As expected, the radio galaxy is unresolved by Chandra but is responsible for approximately half the observed X-ray flux. The remaining ROSAT flux is resolved into four point sources within 1500 of the radio galaxy, corresponding to a surface density 2 orders of magnitude higher than average for X-ray sources at these flux levels [S(0.5–2 keV) > 5 X 10¯16 ergs cm¯² s¯¹]. One of these point sources is identified with a radio-quiet type II quasar at z = 1.863, akin to sources recently reported in deep Chandra surveys. The limit on an extended hot intracluster medium in the Chandra data is S(1–6 keV) < 1.9 X 10¯15 ergs cm¯² s¯¹ (3 σ, 30˝ radius aperture). Though the X-ray observations do not confirm the existence of a massive bound cluster at z > 1, the success of the optical=near-infrared targeting of early-type systems near the radio galaxy validates searches using radio galaxies as beacons for highredshift large-scale structure.We interpret Cl 0442+0202 as a massive cluster in the process of formation.

Spinard, Hyron↗
NASA NTRS2003

Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11

We report the discovery of a galaxy overdensity at z = 1.11 associated with the z = 1.110 high-redshift radio galaxy MG1 J04426+0202 (hereafter MG 0442+0202). The group, Cl 0442+0202, was found in a near-infrared survey of z > 1 radio galaxies undertaken to identify spatially coincident regions with a high density of objects red in I-K' color, typical of z > 1 elliptical galaxies. Spectroscopic observations from the Keck I telescope reveal five galaxies within 35" of MG 0442+0202 at 1.10 < z < 1.11. These member galaxies have broadband colors and optical spectra consistent with passively evolving elliptical galaxies formed at high redshift. Archival ROSAT observations reveal a 3 (sigma) detection of soft X-ray emission coincident with Cl 0442+0202 at a level 5 times greater than expected for the radio galaxy. These data suggest a rich galaxy cluster and inspired a 45 ks Chandra X-Ray Observatory observation. As expected, the radio galaxy is unresolved by Chandra but is responsible for approximately half the observed X-ray flux. The remaining ROSAT flux is resolved into four point sources within 15' of the radio galaxy, corresponding to a surface density 2 orders of magnitude higher than average for X-ray sources at these flux levels [S(0.5-2 keV) > 5 x 10(exp -16) ergs cm (exp -2) s(exp -1)]. One of these point sources is identified with a radio-quiet type II quasar at z = 1.863, akin to sources recently reported in deep Chandra surveys. The limit on an extended hot intracluster medium in the Chandra data is S(1-6 keV) < 1.9 x 10-15 ergs cm (exp -2) s(exp -1) (3 (sigma), 30" radius aperture). Though the X-ray observations do not confirm the existence of a massive bound cluster at z > 1, the success of the optical/near-infrared targeting of early-type systems near the radio galaxy validates searches using radio galaxies as beacons for high-redshift large-scale structure. We interpret Cl 0442+0202 as a massive cluster in the process of formation.

galaxies↗
NASA NTRS1992

Cosmic gamma-ray bursts from BATSE - Another great debate

The BATSE detectors aboard Compton Observatory record about one cosmic gamma-ray burst (GRB) per day. Preliminary data analysis shows a highly isotropic sky map and a nonuniform brightness distribution. Anisotropies expected from a Galactic neutron star population, the most frequently considered source model, did not emerge from the data. Taken at face value, the data seem to suggest a heliocentric solution of the GRB puzzle. The observed isotropy can be achieved if sources are either very near or extragalactic. Pop I neutron stars in the disk do not simultaneously fit sky and brightness distributions. A possibility are sources in an extended Galactic halo with scale length large enough to avoid strong anisotropies due to the solar offset from the Galactic center. If GRBs are located in an extended halo we ask whether the neutron star paradigm can survive. We show that the recently discovered high velocity radio pulsars may provide a natural source population for GRBs. If these pulsars formed in the halo, as suggested by the radio data, the possibility arises that GRBs and high velocity pulsars are two related phenomena that provide observational evidence of the dark Galactic corona. We also discuss cosmological redshift constraints that follow from the observed brightness distribution.

Hartmann, Dieter H.↗
NASA NTRS2012

Toward a New Paradigm for the Unification of Radio Loud AGN and its Connection to Accretion

We recently argued [21J that the collective properties. of radio loud active galactic nuclei point to the existence of two families of sources, one of powerful sources with single velocity jets and one of weaker jets with significant velocity gradients in the radiating plasma. These families also correspond to different accretion modes and therefore different thermal and emission line intrinsic properties: powerful sources have radiatively efficient accretion disks, while in weak sources accretion must be radiatively inefficient. Here, after we briefly review of our recent work, we present the following findings that support our unification scheme: (i) along the broken sequence of aligned objects, the jet kinetic power increases. (ii) in the powerful branch of the sequence of aligned objects the fraction of BLLs decreases with increasing jet power. (iii) for powerful sources, the fraction of BLLs increases for more un-aligned objects, as measured by the core to extended radio emission. Our results are also compatible with the possibility that a given accretion power produces jets of comparable kinetic power.

Georganpoulos, Markos↗
NASA NTRS1982

Radio jets in NGC 4151

The relationship between the radio and optical emissions from the nucleus of the Seyfert galaxy NGC 4151 is investigated by mapping the radio radiation from this source at wavelengths of 20 and 6 cm using the Very Large Array of the National Radio Astronomy Observatory. Results show that the radio emission at wavelengths from 20 to 6 cm extend 10'' (950 pc) along a position angle of 72-84 degrees. This nonthermal emission is found to consist of at least six components and is similar to jets observed in other compact extragalactic radio sources. These radio jets appear to be coincident with the optical line emission region in NGC 4151 and are aligned with the position angle of the linearly polarized optical continuum emission.

Johnston, K. J.↗
NASA NTRS1985

Coordinated observations of X-ray bright BL lacertae objects

Simultaneous multifrequency observations of the BL Lac object Mkn421 covering radio through X-ray wavelengths were performed. Composite multifrequency spectra of the central nonthermal component were obtained at the two epochs after subtracting the optical and infrared light of the underlying galaxy. Physical parameters of Mkn421 are discussed in terms of the synchrotron self-Compton model. Taking the spectral turnover between infrared and radio for synchrotrom self absorption, the radio emmision originates in a more extended region than the infrared to X-ray emission, the source size of which should be less than .01 milliarcseconds. Relativistic beaming is required if the angular size is smaller than a few times .001 milliarcseconds. A possible explanation of the spectral change during the two epochs is also discussed.

Urry, C. M.↗
NASA NTRS1991

Numerical models of extragalactic radio sources

When supercomputer-implemented numerical simulations analyzing the nonlinear physics inherent in the hydrodynamic and MHD equations are applied to extragalactic radio sources, many of the complex structures observed on telescopic images are reproduced. Attention is presently given to recently obtained results from 2D and 3D numerical simulations of the formation and evolution of extended radio morphologies; these numerical models allow the exploration of such physical phenomena as the role of magnetic fields in the dynamics and emissivity of extended radio galaxies, intermittent outflow from the cores of active galaxies, fluid-jet instabilities, and the bending of collimated outflows by motion through the intergalactic medium.

Burns, Jack O.↗
NASA NTRS2000

The Quasar Fraction in Low-Frequency Selected Complete Samples and Implications for Unified Schemes

Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift Survey along with the brighter 3CRR and 6C samples to investigate the fraction of objects with observed broad emission lines - the 'quasar fraction' - as a function of redshift and of radio and narrow emission line luminosity. We find that the quasar fraction is more strongly dependent upon luminosity (both narrow line and radio) than it is on redshift. Above a narrow [OII] emission line luminosity of log(base 10) (L(sub [OII])/W) approximately > 35 [or radio luminosity log(base 10) (L(sub 151)/ W/Hz.sr) approximately > 26.5], the quasar fraction is virtually independent of redshift and luminosity; this is consistent with a simple unified scheme with an obscuring torus with a half-opening angle theta(sub trans) approximately equal 53 deg. For objects with less luminous narrow lines, the quasar fraction is lower. We show that this is not due to the difficulty of detecting lower-luminosity broad emission lines in a less luminous, but otherwise similar, quasar population. We discuss evidence which supports at least two probable physical causes for the drop in quasar fraction at low luminosity: (i) a gradual decrease in theta(sub trans) and/or a gradual increase in the fraction of lightly-reddened (0 approximately < A(sub V) approximately < 5) lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a distinct second population of low luminosity radio sources which, like M8T, lack a well-fed quasar nucleus and may well lack a thick obscuring torus.

Willott, Chris J.↗
NASA NTRS1994

The BL LAC phenomenon: X-ray observations of transition objects and determination of the x-ray spectrum of a complete sample of flat-spectrum radio sources

This report summarizes the activities related to two ROSAT investigations: (1) x-ray properties of radio galaxies thought to contain BL Lac type nuclei; and (2) x-ray spectra of a complete sample of flat-spectrum radio sources. The following papers describing the research are provided as attachments: Multiple X-ray Emission Components in Low Power Radio Galaxies; New X-ray Results on Radio Galaxies; Analysis Techniques for a Multiwavelength Study of Radio Galaxies; Separation of X-ray Emission Components in Radio Galaxies; X-ray Emission in Powerful Radio Galaxies and Quasars; Extended and Compact X-ray Emission in Powerful Radio Galaxies; and X-ray Spectra of a Complete Sample of Extragalactic Core-dominated Radio Sources.

Worrall, Diana M.↗
DOE OSTI2022

Upward propagation of gigantic jets revealed by 3D radio and optical mapping

Occasionally, lightning will exit the top of a thunderstorm and connect to the lower edge of space, forming a gigantic jet. Here, we report on observations of a negative gigantic jet that transferred an extraordinary amount of charge between the troposphere and ionosphere (~300 C). It occurred in unusual circumstances, emerging from an area of weak convection. As the discharge ascended from the cloud top, tens of very high frequency (VHF) radio sources were detected from 22 to 45 km altitude, while simultaneous optical emissions (777.4 nm OI emitted from lightning leaders) remained near cloud top (15 to 20 km altitude). This implies that the high-altitude VHF sources were produced by streamers and the streamer discharge activity can extend all the way from near cloud top to the ionosphere. The simultaneous three-dimensional radio and optical data indicate that VHF lightning networks detect emissions from streamer corona rather than the leader channel, which has broad implications to lightning physics beyond that of gigantic jets.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1976

Observations of intensity and linear polarization of CTB 80 at 6 and 2.8 cm

The paper presents observations of the distribution of intensity and linear polarization over the radio source CTB 80 at 6 and 2.8 cm. The physical nature of the source is examined, particularly the relation between the strong central component and a ridgelike structure that extends across the northern half in the E-W direction. The structure, nonthermal spectrum, and polarization of the central component are found to be very similar to those of a supernova remnant, but the ridge is shown to be unlike any feature of any other SNR. It is suggested that the ridge may have resulted from expansion of the remnant shell into a dense interstellar cloud or, alternatively, that CTB 80 might be a nearby extragalactic radio source similar to Centaurus A.

Velusamy, T.↗
DOE OSTI2020

Multiwavelength Observations of 2HWC J1928+177: Dark Accelerator or New TeV Gamma-Ray Binary?

2HWC J1928+177 is a Galactic TeV gamma-ray source detected by the High Altitude Water Cherenkov (HAWC) Observatory up to ~56 TeV. The HAWC source, later confirmed by the High Energy Stereoscopic System, still remains unidentified as a dark accelerator since there is no apparent supernova remnant or pulsar wind nebula detected in the lower-energy bands. The radio pulsar PSR J1928+1746, coinciding with the HAWC source position, has no X-ray counterpart. In this work, our SED modeling shows that inverse Compton scattering in the putative pulsar wind nebula can account for the TeV emission only if the unseen nebula is extended beyond $r\sim 4^{\prime} $. Alternatively, TeV gamma-rays may be produced by hadronic interactions between relativistic protons from an undetected supernova remnant associated with the radio pulsar and a nearby molecular cloud G52.9+0.1. NuSTAR and Chandra observations detected a variable X-ray point source within the HAWC error circle, potentially associated with a bright infrared (IR) source. The X-ray spectra can be fitted with an absorbed power-law model with N H = (9 ± 3) × 10 22 cm –2 and Γ X = 1.6 ± 0.3 and exhibit long-term X-ray flux variability over the last decade. If the X-ray source, possibly associated with the IR source (likely an O star), is the counterpart of the HAWC source, it may be a new TeV gamma-ray binary powered by collisions between the pulsar wind and stellar wind. Follow-up X-ray observations are warranted to search for diffuse X-ray emission and determine the nature of the HAWC source.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

IRAS colors of VLA identified objects in the galaxy

Infrared Astronomy Satellite (IRAS) sources found within 4 degrees of l = 125 deg, b = 2 deg on the 3rd HCON 60 micron Sky Brightness Images were observed at the Very Large Array (VLA). Regions were to be identified where massive stars are forming by looking for small areas of radio continuum emissions. The IRAS sources could be divided into three groups by their IRAS 12 micron/25 micron and 60 micron/100 micron color. The group identified with star forming regions contained essentially all of the objects with extended radio emission. In all of these cases the extended radio emission showed a morphology consistent with the identification of these objects as HII regions. The conclusion drawn is that star formation regions can be distinguished from other objects by their infrared colors.

Fich, Michel↗
NASA NTRS1983

X-ray, radio, and infrared observations of the 'rapid burster' /MXB 1730-335/ during 1979 and 1980

The paper reports partially simultaneous observations of the 'rapid burster' (MXB 1730-335) at X-ray, infrared, and radio wavelengths, covering several hundred hours during 1979 and 1980. None of the authors of this report saw any infrared or radio bursts. On several occasions an absence of infrared bursting was observed during X-ray bursting. On one occasion an absence of X-ray bursting was observed during a radio burst (4.1 GHz) reported by Calla et al. (1979). To date, radio bursts (a total of at least a dozen) have been reported only by Calla et al. (1980). Considering these and other observations summarized here, the reported radio bursts are either unreal or do not bear a simple relation to the X-ray bursts from the 'rapid burster'. The status of the reported infrared bursts also remain ambiguous. Limits to the brightness of any persistent radio source at the position of MXB 1730-335, limits to persistent X-ray emission during an extended X-ray quiet phase, and a measurement of the infrared polarization in the direction of the X-ray source are also reported.

Lawrence, A.↗
NASA NTRS1985

An X-ray study of M51 (NGC 5194) and its companion (NGC 5195)

Observations of NGC 5194/95 with the Einstein HRI show a very strong nuclear X-ray source, surrounded by a diffuse flux, three point sources, and the companion. The diffuse flux, which correlates well with the radio continuum, is likely to originate from the disk population with an age of approximately 2.1 billion yrs. The large luminosity from the nuclear source, together with optical and radio observations, shows that it belongs to the low luminosity active nuclei, thus extending this class to luminosities of less than about 10 to the 40th erg/s.

Palumbo, G. G. C.↗