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NASA NTRS1980

X-rays from G74.9 + 1.2 - An elderly Crab Nebula

The supernova remnant G74.9 + 1.2, which resembles the Crab Nebula in many of its radio properties, has been detected in 0.15-3 keV X-rays with the Imaging Proportional Counter on the Einstein Observatory. The intrinsic luminosity of the object is about 100 times weaker than the Crab Nebula in this band. The X-ray morphology is centrally brightened (not a shell) with a total extent about 5 arcmin (17 pc). The nearby, intense, compact radio source 2013 + 370 is also probably detected as an extended X-ray source. It is argued that G74.9 + 1.2 represents an object similar to the Crab Nebula but of age 4000-7000 years. If this is the case, the period of the pulsar or neutron star (whose loss of rotational energy fuels the nebula) is predicted to be 0.1-0.2 s.

Wilson, A. S.↗

NASA NTRS1992

12 and 20 micron imaging of the starburst galaxy NGC 253

The study presents 12- and 20-micron imaging of the starburst galaxy NGC 253 with a spatial resolution of 0.8 arcsec. A positional uncertainty of 1.6 arcsec in these images is estimated on the basis of previous ground-based mid-IR studies to determine the absolute position of the images. It is concluded that the proposed 'nucleus' of NGC 253, i.e., the dominant, bright, flat-spectrum radio source identified by Turner & Ho (1985) (TH 2), is not associated with the mid-IR peak, but rather is located 2.2 arcsec to the northeast. The mid-IR peak, IRS 1, is placed midway between TH 6 and TH 7. Several coincidences with the present 12-micron image are found: IRS 1 falls within 1 arcsec of the 2-micron peak; a second significantly weaker IR source, IRS 2, coincides with TH 2; and the brightest steep-spectrum 6-cm radio source, TH 9, coincides with a 'tongue' of emission extending to the southwest of IRS 1.

Pina, R. K.↗

NASA NTRS1998

Low Luminosity States of the Black Hole Candidate GX 339-4: ASCA and Simultaneous Radio/RXTE Observations - 1

We discuss a series of observations of the black hole candidate GX 339-4 in low luminosity, spectrally hard states. We present spectral analysis of three separate archival Advanced Satellite for Cosmology and Astrophysics (ASCA) data sets and eight separate Rossi X-ray Timing Explorer (RXTE) data sets. Three of the RXTE observations were strictly simultaneous with 843 Mega Hertz and 8.3-9.1 Giga Hertz radio observations. All of these observations have (3-9 keV) flux approximately less than 10(exp-9) ergs s(exp-1) CM(exp -2). The ASCA data show evidence for an approximately 6.4 keV Fe line with equivalent width approximately 40 eV, as well as evidence for a soft excess that is well-modeled by a power law plus a multicolor blackbody spectrum with peak temperature approximately equals 150-200 eV. The RXTE data sets also show evidence of an Fe line with equivalent widths approximately equal to 20-1OO eV. Reflection models show a hardening of the RXTE spectra with decreasing X-ray flux; however, these models do not exhibit evidence of a correlation between the photon index of the incident power law flux and the solid angle subtended by the reflector. 'Sphere+disk' Comptonization models and Advection Dominated Accretion Flow (ADAF) models also provide reasonable descriptions of the RXTE data. The former models yield coronal temperatures in the range 20-50 keV and optical depths of r approximately equal to 3. The model fits to the X-ray data, however, do not simultaneously explain the observed radio properties. The most likely source of the radio flux is synchrotron emission from an extended outflow of extent greater than O(10 (exp7) GM/c2).

Wilms, Joern↗

NASA NTRS1981

Radio jet refraction in galactic atmospheres with static pressure gradients

A theory based on the refraction of radio jets in the extended atmosphere of an elliptical galaxy, is proposed for double radio sources with a Z or S morphology. The model describes a collimated jet of supersonic material that bends self-consistently under the influence of external static pressure gradients, and may alternatively be seen as a continuous-jet version of the buoyancy model proposed by Gull (1973). Emphasis is placed on (1) S-shaped radio sources identified with isolated galaxies, such as 3C 293, whose radio structures should be free of distortions resulting from motion relative to a cluster medium, and (2) small-scale, galaxy-dominated rather than environment-dominated S-shaped sources such as the inner jet structure of Fornax A.

Henriksen, R. N.↗

NASA NTRS1989

Distribution of dust in W31 complex

W31 is a H II region/molecular cloud complex in the galactic plane at a distance of 6 Kpc. This complex consists of two prominent radio continuum sources (G10.2-0.3 and G10.3-0.1) representing H II regions. An extended region covering both these H II regions was mapped in the Far IR (FIR) using the TIFR 1 m balloon-borne telescope with an angular resolution of approx. 1 min and a dynamic range of 100. The resulting flux density distribution at an effective wavelength of 160 microns is presented. The coadded IRAS survey scan data at 60 and 100 microns were deconvolved using a maximum entropy method to generate the flux density maps of the same region. These 60 and 100 micron maps are given and are briefly discussed.

Ghosh, Swarna Kanti↗

NASA NTRS1980

Einstein observations of active galaxies

X-ray observations of Cen A (NGC 5128) and seven other X-ray emitting active galaxies are discussed which were made with the imaging proportional counter and the high-resolution imager aboard the Einstein Observatory. In addition to Cen A, the sources observed were the N-type galaxy 3C 120, the quasars OX 169 and 3C 273, and four Class 1 Seyfert galaxies, viz., Mkn 509, Mkn 79, NGC 6814, and NGC 4151. For Cen A, it is found that the X-ray data are dominated by a central point source of about 2 cts/sec, that X-ray elongations (possibly associated with the inner radio lobes) extend in the NE and SW directions, and that an X-ray jet exists which is aligned with the optical jet. The results for the other sources are used to derive emitting-region sizes and black-hole masses for models based on an accreting central black hole.

Tananbaum, H.↗

NASA NTRS1989

Radio-continuum emission from the ionized stellar winds of warm supergiants

The Very Large Array has been used at an observing wavelength of 6 cm to survey 25 supergiants of spectral types between B2 and F8. Only one of these stars (Beta Ori, or Rigel) has been detected as a radio-continuum source, with an inferred 6 cm luminosity L6 of 7 x 10 to the 16th ergs/sec per Hz. Rigel may also be an X-ray source (and, if it were, would be the only X-ray detected star out of the 12 stars in this sample that were observed by Einstein. An extended source of more than 10 mJy flux density with the same angular dimensions and location as He 1-5, the planetary nebula surrounding the peculiar supergiant FG Sge, and a weak localized source of roughly 0.1-0.2 mJy somewhat offset from the center of the extended radio emission have also been detected. The upper limits to L6 for the F Ib stars are as much as an order of magnitude below the level at which Rigel was detected. If the radio emission from Rigel is interpreted as free-free radiation from its stellar wind, the inferred ionized mass-loss rate is 2.5 x 10 th the 7th solar mass/yr. The most stringent upper limits to the ionized mass-loss rates obtained for the F and A supergiants are not greater than 10 to the -8th solar mass/yr and less than or equal to 10 to the -7th solar mass/yr, respectively.

Drake, S. A.↗

NASA NTRS1974

A high-resolution map of the Orion Nebula region at far-infrared wavelengths

It is shown that the Kleinmann-Low nebula continues to radiate like a 70-deg-K blackbody at 69 microns, as it does at shorter wavelengths, but that most of the 69-micron flux from Ori A (M42) comes from an extended emission that roughly follows the free-free radio emission. Nearby sources also detected include the nebula M43 and the molecular cloud OMC-2.

Fazio, G. G.↗

NASA NTRS1975

The earth as a radio source - The nonthermal continuum

It is shown that a weak nonthermal continuum is produced by the earth's magnetosphere extending over a very wide range of frequencies, from 500 Hz in the low-density regions of the magnetotail to above 100 kHz. The frequency spectrum of the continuum radiation consists of two components: a trapped component within the magnetosphere at frequencies below the solar wind plasma frequency and an escaping component propagating freely away from the earth at frequencies above the solar wind plasma frequency. It is also shown that the continuum radiation is generated in a broad region extending through the morning and early afternoon from about 4.0 to 14.0 hours local time immediately beyond the plasmapause boundary, at radial distances from 4.0 to 8.0 earth radii. Possible mechanisms underlying the generation of this radiation are discussed, including the gyrosynchrotron radiation from energetic electrons in the outer radiation zone.

Gurnett, D. A.↗

NASA NTRS1992

The near-infrared counterpart of a variable galactic plane radio source

A near-infrared counterpart to the highly variable, unresolved galactic plane radio source GT 0116 + 622 is identified. This source is of particular interest, as it has been previously suggested to be the counterpart of the gamma-ray source Cas gamma-l. The present NIR and red images detect a faint, spatially extended (3 arcsec FWHM), very red object coincident with the radio position. There is complex spatial structure which may be due in part to an unrelated superposed foreground object. Observations on multiple nights show no evidence for flux variability, despite the high amplitude variability on a time-scale of days reported for the radio source. The data are consistent with an interpretation of GT 0116 + 622 as an unusually variable, obscured active galaxy at a distance of several hundred megaparsecs, although more exotic, and in particular galactic, interpretations cannot yet be ruled out. If the object is extragalactic, the previously suggested identification with the gamma-ray source would seem unlikely.

Margon, Bruce↗

NASA NTRS1984

The Helios radio astronomy experiment

Radio bursts traveling between the Sun and the Earth were tracked by radio astronomy experiments on Helios 1 and 2. A relatively short dipole antenna with a well-defined toroidal reception pattern was flown. The antenna spins in the ecliptic at 60.3 rpm and 2 frequencies are measured in each revolution. The signal analysis determines the strength of the signal, the direction of the source in the ecliptic, and the degree of modulation, and estimates source size. The experiments provide three-dimensional direction finding in space. They extend the radio frequency window beyond what is observable on Earth, and offer a long triangulation baseline.

Kayser, S.↗

NASA NTRS1988

Unusual radio source MG1131+0456 - A possible Einstein ring

The discovery of extremely unusual structure in the radio source MG1131+0456 is reported. In a radio map with subsarcsecond resolution the object appears as an elliptical ring of emission accompanied by a pair of more compact sources, nearly diametrically opposed and offset by about 0.3 arcsec to the southwest of the ring. There is a faint, slightly extended, optical counterpart. A continuum but no emission lines is detected in its spectrum; therefore, the redshift of the counterpart is unknown. The radio morphology suggests that this source may be an example of an 'Einstein ring', a highly symmetric case of gravitational lensing in which the source is imaged into a ring. Other explanations are considered and excluded by the data. Another possibility is that MG1131+04565 represents a new type of astronomical object.

Hewitt, J. N.↗

NASA NTRS1984

5-GHz observations of cores in extended radio galaxies

Results are presented from a search for radio cores at 5 GHz with the VLA in 18 moderately luminous radio galaxies from the second Bologna catalogue. Maps of several of the ten detected cores indicate structure on arcsecond scales in addition to the unresolved central source. Higher-resolution, multifrequency observations are very desirable in future studies of such cores. A statistical study of these and previously observed samples of radio galaxies was then performed. It was found that the radio core luminosity is much stronger in galaxies that are optically bright than faint, and that strong cores tend to occur only in galaxies with luminous extended sources while weak cores can occur in all ranges of extended source luminosity.

Ulrich, M.-H.↗

NASA NTRS1984

Voyager observations of Jovian millisecond radio bursts

Voyager Planetary Radio Astronomy data collected over 30-day intervals centered on the two close encounters with Jupiter were utilized to study the characteristics of millisecond-duration radio bursts (s-bursts) at frequencies between 5 and 15 MHz. In this frequency range, s-bursts are found to occur almost independently of Central Meridian Longitude and to depend entirely on the phase of Io with respect to the observer's planetocentric line of sight. Individual bursts typically cover a total frequency range of about 1.5 to 3 MHz, and they are usually strongly circularly polarized. Most bursts in a particular s-burst storm will exhibit the same polarization sense (either right-hand or left-hand), and there is some evidence for a systematic pattern in which one polarizations sense is preferred over the other as a function of Io phase and Central Meridian Longitude. These data are all suggestive of a radio source that is located along the instantaneous Io flux tube and that extends over a linear dimension of 5000 km along the field lines in both the northern and southern Hemispheres.

Alexander, J. K.↗

NASA NTRS1984

Voyager observations of Jovian millisecond radio bursts

Alexander, J. K.↗

NASA NTRS2004

High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

The authors present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3--0.5 resolution from 4.7 (micro)m to 22 (micro)m. The young stellar objects designed infrared source n and radio source I are believed to dominate the BN/KL region. They have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L(sub (center-dot)).

STARS↗

NASA NTRS1979

Jupiter's magnetosphere and radiation belts

Radioastronomy and Pioneer data reveal the Jovian magnetosphere as a rotating magnetized source of relativistic particles and radio emission, comparable to astrophysical cosmic ray and radio sources, such as pulsars. According to Pioneer data, the magnetic field in the outer magnetosphere is radially extended into a highly time variable disk-shaped configuration which differs fundamentally from the earth's magnetosphere. The outer disk region, and the energetic particles confined in it, are modulated by Jupiter's 10 hr rotation period. The entire outer magnetosphere appears to change drastically on time scales of a few days to a week. In addition to its known modulation of the Jovian decametric radio bursts, Io was found to absorb some radiation belt particles and to accelerate others, and most importantly, to be a source of neutral atoms, and by inference, a heavy ion plasma which may significantly affect the hydrodynamic flow in the magnetosphere. Another important Pioneer finding is that the Jovian outer magnetosphere generates, or permits to escape, fluxes of relativistic electrons of such intensities that Jupiter may be regarded as the dominant source of 1 to 30 MeV cosmic ray electrons in the heliosphere.

Kennel, C. F.↗

NASA NTRS2013

The Atacama Cosmology Telescope: Likelihood for Small-Scale CMB Data

The Atacama Cosmology Telescope has measured the angular power spectra of microwave fluctuations to arcminute scales at frequencies of 148 and 218 GHz, from three seasons of data. At small scales the fluctuations in the primordial Cosmic Microwave Background (CMB) become increasingly obscured by extragalactic foregounds and secondary CMB signals. We present results from a nine-parameter model describing these secondary effects, including the thermal and kinematic Sunyaev-Zel'dovich (tSZ and kSZ) power; the clustered and Poisson-like power from Cosmic Infrared Background (CIB) sources, and their frequency scaling; the tSZ-CIB correlation coefficient; the extragalactic radio source power; and thermal dust emission from Galactic cirrus in two different regions of the sky. In order to extract cosmological parameters, we describe a likelihood function for the ACT data, fitting this model to the multi-frequency spectra in the multipole range 500 < l < 10000. We extend the likelihood to include spectra from the South Pole Telescope at frequencies of 95, 150, and 220 GHz. Accounting for different radio source levels and Galactic cirrus emission, the same model provides an excellent fit to both datasets simultaneously, with χ2/dof= 675/697 for ACT, and 96/107 for SPT. We then use the multi-frequency likelihood to estimate the CMB power spectrum from ACT in bandpowers, marginalizing over the secondary parameters. This provides a simplified 'CMB-only' likelihood in the range 500 < l < 3500 for use in cosmological parameter estimation

Cosmology↗