Engineering topics

Long, K. S.

Publications and source records attributed to Long, K. S..

At least 19 records

NASA NTRS2014

Super-Eddington Mechanical Power of an Accreting Black Hole in M83

Mass accretion onto black holes releases energy in the form of radiation and outflows. Although the radiative flux cannot substantially exceed the Eddington limit, at which the outgoing radiation pressure impedes the inflow of matter, it remains unclear whether the kinetic energy flux is bounded by this same limit. Here, we present the detection of a radio-optical structure, powered by outflows from a non-nuclear black hole. Its accretion disk properties indicate that this black hole is less than 100 solar masses. The optical-infrared line emission implies an average kinetic power of 3 × 10(exp 40) erg second(exp -1), higher than the Eddington luminosity of the black hole. These results demonstrate kinetic power exceeding the Eddington limit over a sustained period, which implies greater ability to influence the evolution of the black hole's environment.

uper-Eddington Mechanical Power↗

NASA NTRS2014

Dust Production and Particle Acceleration in Supernova 1987A Revealed with ALMA

Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/ Submillimeter Array to observe SN1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 μm, 870 μm, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 Solar Mass). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.

Particle↗

NASA NTRS2011

Herschel Detects a Massive Dust Reservoir in Supernova 1987A

We report far-infrared and submillimeter observations of Supernova 1987A, the star that exploded on February 23, 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of approx.17-23 K at a rate of about 220 stellar luminosity. The intensity and spectral energy distribution of the emission suggests a dust mass of approx.0.4-0.7 stellar mass. The radiation must originate from the SN ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high red shifts.

Matsuura, M.↗

NASA NTRS1995

ROSAT observations of the supernova remnant 3C 400.2

We have used the ROSAT point source proportional counter (PSPC) to examine the X-ray emission from 3C 400.2, a supernova remnant (SNR) which is a member of a class of remnants with limb-brightened radio and centrally condensed X-ray morphologies. The X-ray emission fills the radio shell and is characterized by an interior peak in the northwest region of the remnant. Otherwise, the surface brightness has a relatively smooth distribution. The X-ray peak is not correlated with any radio features or with the observed optical filaments. The PSPC X-ray spectrum is not well fitted by a power-law model but can be described in terms of thermal emission from a hot plasma with solar abundances. The only point source along the line of sight to the SNR is associated with a bright foreground F8 star. Thus the X-ray emission from 3C 400.2 is unlikely to be due to synchrotron radiation from an active pulsar. If the emission arises from a thermal plasma and the absorbing column along the line of sight to 3C 400.2 is 7.8 x 10(exp 21)sq cm, then the temperature of the plasma is 0.27 keV, and the 0.4-2.4 keV X-ray luminosity is 1.3 x 10(exp 36) ergs/s for an assumed distance of 6 kpc. An X-ray hardness ratio map shows a slight increase in the hardness of the emission in the regions of the remnant with a higher X-ray surface brightness. Assuming uniform absorption across the remnant, this increase implies the temperature is approximately 1.5 times greater in the high surface brightness regions of SNR. The relatively uniform spectrum and the anticorrelation between X-ray and radio features seems to rule out the possibility that 3C 400.2 is actually two overlapping or interacting SNRs. The morphology of 3C 400.2 can be explained in terms of a multiphase interstellar medium (ISM) in which the primary shock is expanding into an ISM studded with dense cloudlets, if the clouds are evaporated or disrupted on a timescale which is long compared to the age of the SNR. It may also be possible to explain the emission in terms of the interaction of the SNR with a massive wind-driven shell, although the existing models for the evolution of A SNR in this environment suggest that the H-alpha luminosity should be much larger than the X-ray luminosity, which is not observed. We cannot completely rule out the possibility that 3C 400.2's appearance as a centrally peaked X-ray SNR is the result of an interaction between the remnant and a cloud along the line of sight, although this seems unlikely.

Saken, Jon M.↗

NASA NTRS1993

Sub-Lyman-alpha observations of supernova remnants

The first map of O VI lambda 1035 emission of the Cygnus Loop has now been obtained with Voyager. The first good spectra of the sub-Lyman-alpha region in the Cygnus Loop and in the Large Magellanic Cloud (LMC) remnant N49 have been obtained with the Hopkins Ultraviolet Telescope. The lines detected below 1200 A include S VI lambda lambda 933,945, C III lambda 977, N III lambda 991, and O VI lambda lambda 1032,1038. The O VI luminosities of the Cygnus Loop and of N49 exceed their soft X-ray luminosities. There is O VI emission at the primary shock front in the Cygnus Loop and from the bright optical filaments. The HUT spectra of the Cygnus Loop can be interpreted in terms of shocks with velocities of 170-190 km/s; the differences between the two spectra are due to the time since the beginning of the shock-cloud encounter.

Long, K. S.↗

NASA NTRS1992

The spectrum of the tropical oxygen nightglow observed at 3 A resolution with the Hopkins Ultraviolet Telescope

Ultraviolet spectra of the tropical oxygen nightglow in the range of 830 to 1850 A (in first order) at 3 A resolution were obtained with the Hopkins Ultraviolet Telescope in December 1990. The data are presented which were obtained on a setting celestial target as the zenith angle of the line-of-sight varied from 77 to 95 deg. The dominant features in the spectrum (other than geocoronal hydrogen) are O I 1304 and 1356 and the radiative recombination continuum near 911 A. The continuum is resolved and found to be consistent with an electron temperature in the range 1000-1250 K. The observed ratio of the brightness of O I 1356 to the continuum suggests that O(+)-O(-) mutual neutralization contributes about 40 percent to the 1356 A emission. The dependence of the optically thin emissions on zenith angle is consistent with a simple ionospheric model. Weak O I 989 emission is also detected, but there is no evidence for any similarly produced atomic nitrogen emissions.

Feldman, P. D.↗

NASA NTRS1985

Complex structure of the supernova remnant HB 3

HB 3 is an old, large (84 pc diameter) supernova remnant associated with the W3 H II region/molecular cloud complex. Observations of the imaging proportional counter (IPC) onboard the Einstein X-ray astronomy satellite have been reprocessed to yield a contour map of X-ray brightness and spectra of various regions of this remnant. The measured IPC flux is 2.4 x 10 to the -11th ergs per sq cm per s, giving a 0.2-4 keV luminosity of 1.6 x 10 to the 35th ergs/s for a column densityof 6 x 10 to the 21st per sq cm. The measured X-ray temperatures reveal a decrease from center to limb of the remnant of 1-0.3 keV. HB 3 is in the late adiabatic blast-wave phase of evolution, 30,000 to 50,000 yr old and with an initial blast energy of 3 x 10 to the 50th ergs. The X-ray map is compared with available radio and optical images. In X-rays, HB 3 has two components - a diffuse emission inside the 84 pc radio remnant and a ring of emission at the center of 30 pc in diameter. The diffuse emission is similar to that from other supernova remnants which are moderately obscured (column density, nH approximately 10 to the 22nd per sq cm). Three possibilities for the origin of the ring are explored: (1) a second supernova remnant, (2) a shocked shell in the interstellar medium surrounding HB 3, and (3) reverse-shock heated ejecta. There is no hot neutron star within the remnant.

Leahy, D. A.↗

NASA NTRS1985

Extragalactic supernova remnants

Because the supernova remnants (SNRs) in other galaxies are at well-defined distances and because in many cases the reddening within extragalactic samples is more uniform than is the case for the Galactic SNR sample, extragalactic SNRs are fundamental to improving the understanding of SNR evolution. Here methods for identifying SNRs are reviewed and the current status of observational research is explored. The data do not unambiguously support the simple Sedov picture of SNR expansion, although it may be that the data can be reconciled with this picture if sufficient variation in initial conditions is allowed.

Long, K. S.↗

NASA NTRS1985

An intensified photodiode array detector for space applications

The Hopkins Ultraviolet Telescope (HUT) is a general purpose moderate resolution spectrograph which is now being constructed for launch on the Space Shuttle. The instrument contains a Rowland spectrograph, which is located at the prime focus of a 0.9-m f/2 parabola. A description is given of the progress which has been made in the development of a flight detector for HUT. The detector developed is an intensified photodiode array. The image intensifier part of the detector contains two 25-mm 80:1, 12-micron pore microchannel plates (PCPs). A thin layer of CsI deposited on the front surface of the first microchannel plate has the objective to increase the quantum efficiency of the detector below 1850 A. The detector system utilizes a spectrometer processor (SP) which is based upon a bit-sliced microprocessor. The current status of the HUT detector system is discussed, and aspects of performance are evaluated. It is felt that the developed system will meet or exceed the design requirements.

Long, K. S.↗

NASA NTRS1985

X-ray images of W28 and 3C400.2 - Two radio-shell supernova remnants with centrally-peaked X-ray emission

X-ray images of the supernova remnants (SNRs) W28 and 3C400.2 were obtained using the Imaging Proportional Counter (IPC) on the Einstein Observatory. Despite the shell-like radio morphology of these remnants, their X-ray emission is centrally peaked. Two possible X-ray emission mechanisms are explored: synchrotron emission due to an active central pulsar, and thermal emission from a thin hot plasma filling the interior of the remnant. Comparisons of X-ray and radio properties of W28 and 3C400.2 with known Crab-like remnants suggest that synchrotron emission is not a very plausible X-ray emission mechanism. Optical and radio observations suggest that both SNRs exploded in a dense cloud and have evolved rapidly to the radiative stage. The X-ray morphology observed is similar to that predicted for SNRs in such an environment.

Matsui, Y.↗

NASA NTRS1984

A detailed X-ray and radio comparison of Kepler's supernova remnant

High-resolution radio images of Kepler's SNR (SNR (SN 1604) at 6 and 21 cm have been obtained using the VLA. The orientation of linear polarization in the SNR implies a substantial nonrandom radial component for the magnetic field of the remnant. Based on a new X-ray picture of the SNR, obtained using the Einstein Observatory, a detailed comparison of the X-ray and radio morphology is carried out. There is a good correlation between rotation measure, obtained from the radio maps, and emission measure, an X-ray-derived quantity in the SNR shell. From the mean electron density value infered from an analysis of X-ray fluxes, a mean radial magnetic field of 14 micro G and a total magnetic field of 70 microG are estimated. The energy density of relativistic electrons in Kepler's SNR in the shell comparable to the energy density in the magnetic field; the relativistic electron-pressure is 2 percent of the thermal gas pressure. The strong correlation between radio emissivity and X-ray emissivity found over the SNR in somewhat large scale can be ascribed to acceleration of thermal electrons at the shock wave and insignificant diffusion of resultant relativistic electrons.

Matsui, Y.↗

NASA NTRS1984

A search for X-ray polarization in cosmic X-ray sources

Fifteen strong X-ray sources were observed by the X-ray polarimeters on board the OSO 8 satellite from 1975 to 1978. The final results of this search for X-ray polarization in cosmic sources are presented in the form of upper limits for the 10 sources which have not been discussed elsewhere. These limits in all cases are consistent with a thermal origin for the X-ray emission.

Hughes, J. P.↗

NASA NTRS1984

Einstein Observations of the Cygnus Loop

The imaging instruments on the Einstein Observatory were used to study the detailed X-ray structure of the Cygnus Loop. An arc minute resolution map of the 0.1-4.0 keV emission from the entire remnant was obtained with the imaging proportional counter (IPC). The bright northeastern and western limbs were mapped with the high resolution imager (HRI). The large-scale structure of the Loop is well modeled as a limb-brightened shell of hot gas at 2 x 10 to the 6th K created by the expansion of a blast wave into an inhomogeneous interstellar medium. The pulse-height data from the IPC indicate that the center of the remnant is generally hotter than the limb with temperatures as high as 4 x 10 to the 6th K. The X-ray maps show good general correlation with large-scale radio and optical structure, and in some cases good detailed correlation with faint optical filaments dominated by hydrogen line emission.

Ku, W. H.-M.↗

NASA NTRS1983

Supernova remnants in the Magellanic Clouds

The present updated catalog of SNRs in the Large and Small Magellanic Clouds (LMC and SMC) incorporates remnants recently discovered as a result of coordinated X-ray, optical, and radio surveys, and contains 25 confirmed SNRs in the LMC and six in the SMC. Optical images are included for all of the new SNRs, together with X-ray isophotes for 24 of the SNRs in the LMC which have been obtained with the high resolution imager and imaging proportional counter of the Einstein Observatory. The cumulative number-diameter relation for Type II SNRs with D smaller than 50 pc in the LMC is N(D)= 0.36 D exp 1.0 + or 0.2, suggesting that the SNRs have evolved much faster than expected from Sedov theory and that the free expansion phase dominates their evolution up to diameters of 30-40 pc. SNR production frequencies in the LMC and SMC are calculated to be 1/275 and 1/800 years, respectively, or nearly equal to the galaxies' luminosity ratios.

Mathewson, D. S.↗

NASA NTRS1983

A search for X-ray polarization in cosmic X-ray sources

Fifteen strong X-ray sources were observed by the X-ray polarimeters on board the OSO-8 satellite from 1975 to 1978. The final results of this search for X-ray polarization in cosmic sources are presented in the form of upper limits for the ten sources which are discussed elsewhere. These limits in all cases are consistent with a thermal origin for the X-ray emission.

Hughes, J. P.↗

NASA NTRS1983

The X-ray surface brightness of Kepler's supernova remnant

The first X-ray images of Kepler's supernova remnant (SN Ophiuchi 1604) are presented, and consequences for SNR models are discussed. Observations made with the Einstein Observatory Imaging Proportional Counter and High Resolution Imager show the remnant to be circular, with a strong shell brighter in the north than in the south. A flux of 1.2 x 10 to the -10th ergs/sq cm per sec was measured in the 0.15-4.5 keV region, which corresponds to an X-ray luminosity of 1.0 x 10 to the 36th ergs/sec at a distance of 5 kpc and an interstellar medium density of 2.8 x 10 to the 21st/sq cm. The X-ray observations do not allow the determination of whether the SNR is in the adiabatic or free expansion phase, but in either case it is shown that the mean ISM density must be greater than about 0.1/cu cm. In addition, the density of the X-ray emitting gas must be high, and its electron temperature must be fairly low. The high ISM densities derived for Kepler's SNR and other SNRs thus suggest an atypical ISM, possibly influenced by mass lost from the pre-supernova star.

White, R. L.↗

NASA NTRS1983

X-ray emission from normal galaxies

The results of Einstein Observatory studies of X-ray emission from normal galaxies, including the LMC and SMC, M31, M33, M101, NGC 247, M81 and M100, and N253 are surveyed. The X-ray luminosity of normal galaxies is proportional to their optical luminosity, revealing no strong dependence on galaxy type. The number of individual sources detected are comparable to the number of sources expected on mass considerations. There are substantial numbers of X-ray sources in the Magellanic Clouds with luminosities in the range 10 to the 35th-36th ergs/s, lower than most X-ray binaries but higher than known uncollapsed stellar systems. About seven X-ray sources with luminosities of at least 10 to the 39th ergs/s in the 0.5-3.0 keV band have been found in the arms of nearby spiral galaxies.

Long, K. S.↗

NASA NTRS1983

The X-ray properties of supernova remnants in the Large Magellanic Cloud

Einstein Observatory instruments were used to survey the generic properties of LMC supernova remnants (SNR). The study covered the diffuse optical bar, the 30 Dor nebula, the surrounding H I cloud, and a high fraction of the spiral arms. Twelve SNRs were identified as X-ray sources and two SNR, N157B and 0540 - 69.3, were located from radio emissions. Filamentary H-alpha emissions also revealed five other objects. X-ray intensity data indicated that density levels of the matter surrounding SNR decrease with SNR diameter. The data suggest that Sedov models for SN may not be accurate for LMC SN, which exhibit too great a luminosity scatter in the surrounding interstellar material. The emissions may be accounted for by ejecta from the SN or by multiphase interstellar material.

Long, K. S.↗