Engineering topics

Hughes, John P.

Publications and source records attributed to Hughes, John P..

At least 55 records · Page 3

NASA NTRS1999

ROSAT PSPC and HRI Observations of Supernova Remnant G292.0+1.8

The supernova remnant G292.0+1.8 was observed by the ROSAT PSPC for 18 ksec as part of this grant. Considerable effort was put into the analysis of the PSPC spectra. The major work went into nonequilibrium ionization joint spectral fits with the Einstein SSS and EXOSAT ME data which indicated that the two spatial regions of this remnant (a central bar and a plateau region covering a larger extent) had similar abundances, but different excitation conditions (temperature and ionization state), an important conclusion, if true. Unfortunately as this work was being finished, new ASCA data revealed the presence of a previously unknown, spectrally hard X-ray source near the center of the remnant which contaminated the SSS and ME data and as a consequence made our detailed spectral analysis done up until then un-publishable. We searched for evidence of this hard source in the PSPC data both spectrally and using timing searches (for a pulsar), but found nothing significant. ROSAT HRI data were also obtained on this remnant. These data were compared to the Einstein HRI data to search for evidence of spectral variations with position and possible expansion of the X-ray remnant. One feature in the remnant appears to have changed in brightness although it is not clear what is the cause of the change. No evidence for the hard ASCA source was apparent in the HRI data.

Hughes, John P.↗

NASA NTRS1998

A Very Hot, High Redshift Cluster of Galaxies: More Trouble for Omega(0) = 1

We have observed the most distant (= 0.829) cluster of galaxies in the Einstein Extended Medium Sensitivity Survey (EMSS), with the ASCA and ROSAT satellites. We find an X-ray temperature of 12.3 (sup +3.1) (sub -2.2)keV for this cluster, and the ROSAT map reveals significant substructure. The high temperature of MS1054-0321 is consistent with both its approximate velocity dispersion, based on the redshifts of 12 cluster members we have obtained at the Keck and the Canada-France-Hawaii telescopes, and with its weak lensing signature. The X-ray temperature of this cluster implies a virial mass approx. 7.4 x 10 (sup 14) h (sup -1) M (circle dot), if the mean matter density in the universe equals the critical value (OMEGA (sub 0) = 1), or larger if OMEGA (sub 0) is less than 1. Finding such a hot, massive cluster in the EMSS is extremely improbable if clusters grew from Gaussian perturbations in an OMEGA (sub 0) = 1 universe. Combining the assumptions that OMEGA (sub 0) = 1 and that the initial perturbations were Gaussian with the observed X-ray temperature function at low redshift, we show that this probability of this cluster occurring in the volume sampled by the EMSS is less than a few times 10 (sup -5). Nor is MS1054-0321 the only hot cluster at high redshift; the only two other z greater than 0.5 EMSS clusters already observed with ASCA also have temperatures exceeding 8 keV. Assuming again that the initial perturbations were Gaussian and OMEGA (sub 0) = 1, we find that each one is improbable at the less than 10 (sup -2) level. These observations, along with the fact that these luminosities and temperatures of the high-z clusters all agree with the low-z L (sub X) - T (sub X) relation, argue strongly that OMEGA (sub 0) less than 1. Otherwise, the initial perturbations must be non-Gaussian, if these clusters' temperatures do indeed reflect their gravitational potentials.

Donahue, Megan↗

NASA NTRS1996

ROSAT PSPC Observations of CL0016+16

This report is an update of progress on NASA grant NAG5-2156. The following papers which were published or submitted since April 1966 were supported by this grant. Preprints of each are attached: HST Observations of Oxygen-rich Supernova Remnants in the Magellanic Clouds, and SuperNova Remnants Associated with Molecular Clouds in the Large Magellanic Cloud.

Hughes, John P.↗

NASA NTRS1996

ROSAT PSPC Observations of CL0016+16

Several ROSAT observations concerning with complex spatial structures in Sunyaev-Zel'dovich decrement clusters Abell 665 and CL0016+16, discovery of Be/X-ray stars in two supernova remnants in the Small Magellanic Cloud, a new transient pulsar in the Small Magellanic Cloud with an unusual x-ray spectrum, a new x-ray-discovered cluster of galaxies associated with CL0016+16, and the distance to CL0016+16 vs. the Hubble constant, are presented.

Hughes, John P.↗

NASA NTRS1995

ASCA observations of the Large Magellanic Cloud supernova remnant sample: Typing supernovae from their remnants

We present our first results from a study of the supernova remnants (SNRs) in the Large Magellanic Cloud (LMC) using data from ASCA. The three remnants we have analyzed to date, 0509-67.5, 0519-69.0, and N103B, are among the smallest, and presumably also the youngest, in the Cloud. The X-ray spectra of these SNRs show strong K alpha emission lines of silicon, sulfur, argon, and calcium with no evidence for corresponding lines of oxygen, neon, or magnesium. The dominant feature in the spectra is a broad blend of emission lines around 1 keV which we attribute to L-shell emission lines of iron. Model calculations (Nomoto, Thielemann, & Yokoi 1984) show that the major products of nucleosynthesis in Type Ia supernovae (SNs) are the elements from silicon to iron, as observed here. The calculated nucleosynthetic yields from Type Ib and II SNs are shown to be qualitatively inconsistent with the data. We conclude that the SNs which produced these remnants were of Type Ia. This finding also confirms earlier suggestions that the class of Balmer-dominated remnants arise from Type Ia SN explosions. Based on these early results from the LMC SNR sample, we find that roughly one-half of the SNRs produced in the LMC within the last approximately 1500 yr came from Type Ia SNs.

Hughes, John P.↗

NASA NTRS1995

Evidence for elemental variation in the ejecta of the Tycho supernova remnant

We present an X-ray study of the Tycho supernova remnant utilizing archival data from the high-resolution imagers (HRIs) on Einstein and ROSAT, the low-energy imaging telescopes (LEITs) on EXOSAT, and spectral data from the Broad Band X-ray Telescope (BBXRT). We have made use of the differing HRI bandpasses to construct images of Tycho in two spectral bands, o.7-1.8 keV and 1.8-4.5 keV. We find that the two images differ, with the harder image showing enhanced emission along much of the south, west, and north periphery. There appears to be enhanced soft emission in the interior and in one particular knot of emission in the southeast. Besides continuum (which we model here as thermal bremsstrahlung emission), we believe the hard image shows primarily the distribution of high-ionization Si and S K-shell lines which lie in the 1.8-2.6 keV band, while the softer image has contributions from Si as well as Fe XVII to Fe XXIV L-shell lines in the 0.7-1.4 keV band. Guided by the results of nonequilibrium ionization modeling of the BBXRT spectral data, we interpret the observed contrast in hard and soft X-ray emission in terms of variations in abundance, ionization timescale, and temperature. The most likely explanation for the spectral differences are spatial variations of the relative abundances of Si, S, and Fe.

Vancura, O.↗

NASA NTRS1994

Abundance gradients in cooling flow clusters: Ginga Large Area Counters and Einstein Solid State Spectrometer spectra of A496, A1795, A2142, and A2199

We analyze the Ginga Large Area Counters (LAC) and Einstein Solid State Spectrometer (SSS) spectra of four cooling flow clusters, A496, A1795, A2142, and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high-energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four clusters, with varying degrees of model dependence and statistical significance: the evidence is statistically strongest for A496 and A2142, somewhat weaker for A2199 and weakest for A1795. We also explore the model dependence in the amount of cold, X-ray-absorbing matter discovered in these clusters by White et al.

White, Raymond E., III↗

NASA NTRS1994

Nonpolytropic model for the Coma Cluster

In this article we demonstrate, for the first time, how a physically motivated static model for both the gas and galaxies in the Coma Cluster of galaxies can jointly fit all available X-ray and optical imaging and spectroscopic data. The principal assumption of this nonpolytropic model (Cavaliere & Fusco-Femiano 1981, hereafter CFF), is that the intracluster gas temperature is proportional to the square of the galaxy velocity dispersion everywhere throughout the cluster; no other assumption about the gas temperature distribution is required. After demonstrating that the CFF nonpolytropic model is an adequate representation of the gas and galaxy distributions, the radial velocity dispersion profile, and the gas temperature distribution, we derive the following information about the Coma Cluster: 1. The central temperature is about 9 keV and the central density is 2.8 x 10(exp -3)/cm(exp 3) for the X-ray emitting plasma; 2. The binding mass of the cluster is approximately 2 x 10(exp 15) solar mass within 5 Mpc for (H(sub 0) = 50 km/sec/Mpc), with a mass-to-light ratio of approximately 160 solar mass/solar luminosity; 3. The contribution of the gas to the total virial mass increases with distance from the cluster center, and we estimate that this ratio is no greater than approximately 50% within 5 Mpc. The ability of the CFF nonpolytropic model to describe the current X-ray and optical data for the Coma Cluster suggests that a significant fraction of the thermal energy contained in the hot gas in this as well as other rich galaxy clusters may have come from the interaction between the galaxies and the ambient cluster medium. interaction between the galaxies and the ambient cluster medium.

Fusco-Femiano, R.↗

NASA NTRS1994

Various Roentgen satellite (ROSAT) related studies

The first six months was spent obtaining ROSAT Survey data for as many Slew Survey sources as possible. ROSAT Survey (RASS) counterparts for 605 of the 819 Slew sources (or 75 percent). were found at MPE, providing RASS positions, fluxes, and hardness ratios. The positions were used immediately to confirm or reject proposed catalog identifications from SIMBAD and NED, and to begin a program of identifying new BL Lac objects with high efficiency. In the final six months of the award, extensive analysis were preformed on the RASS counterpart data at Cambridge screening Slew sources with multiple RASS counterparts (up to 23); extended sources and sources with large discrepancies between the RASS and Slew positions. The possibly highly absorbed sources were also studied. Finally, the RASS data has helped to identify optical counterparts to Slew Survey sources - BL Lacs stars, and 'blank fields'.

Stauffer, John R.↗

NASA NTRS1994

A new transient pulsar in the Small Magellanic Cloud with an unusual x-ray spectrum

This article reports the discovery of a luminous (3.5 x 10(exp 37) ergs/sec over the 0.2 to 2 keV band) transient X-ray pulsar in the Small Magellanic Cloud (SMC) with an extremely soft component to its X-ray spectrum. This is the first time that a spectrum of this type has been seen in this class of X-ray source. The pulse period is 2.7632 s, and the pulse modulation appears to vary with energy from nearly unpulsed in the low-energy band of the ROSAT Position Sensitive Proportional Counter (PSPC) (0.07 to 0.4 keV) to about 50% in the high-energy band (1.0 to 2.4 keV). The object, RX J0059.2-7138, also shows flickering variability in its X-ray emission on timescales of 50 to 100s. The pulse-phase-averaged PSPC X-ray spectrum can be well described by a two-component source model seen through an absorbing column density of approximately 10(exp 21) atoms cm(exp -2). One spectral component is a power law with photon index 2.4. The other component is significantly softer and can be described by either a steeply falling power law or a blackbody with a temperature KT(sub BB) approximately 35 eV. Ths component is transient, but evidently upulsed, and, for the blackbody model fits, requires a large bolometric luminosity: near, or even several times greater than, the Eddington luminosity for a 1.4 solar mass object. When these characteristics of its soft emission are considered, RX J0059.2-7138 appears quite similar to other X-ray sources in the magellanic Clouds, such as CAL 83, CAL 87, and RX J0527.8-6954, which show only extreme ultrasoft (EUS) X-ray spectra. The discovery of RX J0059.2-7138, a probably high-mass X-ray binary, clearly indicates that EUS spectra may arise from accretion-powered neutron-star X-ray sources. This result lends support to the idea that some of the 'pure' EUS sources may be shrouded low-mass X-ray binaries rather than accreting white dwarfs.

Hughes, John P.↗

NASA NTRS1994

Discovery of Be/x-ray stars in two supernova remnants in the Small Magellanic Cloud

We present ROSAT high resolution x-ray images of two previously cataloged supernova remnants in the Small Magellanic Cloud (SMC): 0101-72.4 and 0104-72.3. These remnants were known to show optical, x-ray, and radio emission based on earlier observations: the present data show the first evidence for arcsecond-scale x-ray structure. There is no diffuse x-ray emission associated with the optically emitting shell in 0101-72.4; we set a 3 sigma upper limit of 7 x 10(exp 34) erg s(exp -1) on the 0.02-2 keV luminosity from the region. The x-ray emission comes instead from a weak pointlike object near the limb of the remnant. Optical observations of this source reveal a m(sub v) = 14.8 blue star with H alpha and H beta in emission; we identify this as a Be star in the SMC. No evidence for variability down to time scales of about 1 s was found in the ROSAT data; however, a comparison of the ROSAT and Einstein fluxes indicates possible long term variability by a factor of approximately 2 over several years. The other SNR, 0104-72.3, also contains a pointlike x-ray source with a blue optical counterpart (m(sub v) = 16.7) and H alpha emission. We tentatively identify this as a Be star as well. In addition to the point source there is weak diffuse x-ray emission from 0104-72.3 (L(sub x) approximately 1.4 x 10(exp 35) erg s(exp -1)), but the remnant's appearance in the x-ray band is considerably different from that in either the radio or optical band. We argue for a physical association between the supernova remnants (SNRs) and Be/x-ray stars. A large space velocity (greater than or approximately 100 km s(exp -1)) for the Be/x-ray binaries is required if the explosions that produced the remnants also formed the neutron stars in the binaries. Alternatively, the associations could be the result of common membership in OB associations in the SMC.

Hughes, John P.↗

NASA NTRS1994

Elemental abundances of the supernova remnant G292.0+1.8: Evidence for a massive progenitor

We present a comprehensive nonequilibrium ionization (NEI) analysis of X-ray spectral data from the Einstein Observatory and EXOSAT for the supernova remnant G292.0+1.8. The spectra are well described by a single-temperature, single-timescale NEI model with kT = 1.64(sub -0.19)(sup +0.29) keV and n(sub e)t = (5.55(sub -1.12)(sup +1.2) x 10(exp 10)s/cu cm, which establishes that this remnant is indeed young and in the ionizing phase of evolution of its X-ray spectrum. We determine the abundances of the elements O, Ne, Mg, Si, S, Ar, and Fe and examine their variation over the allowed range of column density, kT, and n(sub e)t. Numerical calculations of the nucleosynthesis expected for a 25 solar mass progenitor agree best with the fitted abundances; in fact the minimum rms percent difference between this model and the derived abundances is only 15%. From the fitted emission measure and a simple geometric model of the remnant we estimate the mass of X-ray-emitting plasma to be 9.3(sub -6.2)(sup +1.19) solar mass, for an assumed distance of 4.8 +/- 1.6 kpc. Additional errors on this mass estimate, from clumping of the ejecta, for example, may be substantial. No evidence was found for a difference in the thermodynamic state of the plasma as a function of elemental composition based on analysis of the individual ionization timescales of the various species. In this sense then, G292.0+1.8 resembles the remnant Cas A (another product of a massive star supernova), while it is different from the remnants of SN 1572 (Tycho) and SN 1006, both of which are believed to be from Type Ia supernovae.

Hughes, John P.↗

NASA NTRS1994

X-ray spectroscopy of SNR E0102-72 with the ASCA satellite

The Advanced Satellite for Cosmology and Astrophysics (ASCA) satellite has obtained a moderate-resolution energy spectrum of E0102-72, the brightest Supernova Remnant (SNR) in the Small Magellanic Cloud (SMC). This paper reports on the first results of the analysis of the high quality spectrum of E0102-72. The spectrum shows resolved emission lines of He-like K alpha, H-like K alpha and K beta from oxygen, neon, and magnesium. The intensity ratios of these lines cannot be explained by a multi-component plasma model with uniform abundances, but requires abundance inhomogeneity in the plasma. We demonstrate how the spectral capabilities of the ASCA SIS make available new diagnostics of X-ray plasmas in a state of non-equilibrium ionization. Some interpretation based on the spectral analysis is also given.

Hayashi, Ichizo↗

NASA NTRS1994

Detection of X-rays from SN 1987A with ROSAT

Soft X-rays (0.5-2 keV) were detected with the ROSAT Position-Sensitive Proportional Counter (PSPC) from the direction of SN 1987A, which falls within an association in the Large Magellanic Cloud (LMC) that is rich in B stars. The emission is consistent with two point sources in the LMC with total luminosity of approximately 10(exp 34) ergs/s. The brighter source is identified with SN 1987A on the basis of its positional agreement. We interpret the emission as arising from the interaction of supernova ejecta with the pre-existing blue giant wind. The second source may be an unidentified Be/X-ray binary. Another possibility is that the second source is an X-ray echo from the supernova outburst. The X-ray echo interpretation reqires that the supernova emitted approximately 10(exp 47) ergs in a burst of soft X-rays.

Gorenstein, Paul↗

NASA NTRS1994

ROSAT HRI observations of Magellanic Cloud supernova remnants

Analysis of deep ROSAT high resolution imager (HRI) observations of two oxygen-rich supernova remnants (SNR's) in the Magellanic Clouds is described. For N132D, I exploit the limited spectral information provided by the HRI to investigate arcsecond scale spectral variations. I find that there is a region of harder X-ray emission near the southern limb and regions of softer emission near the center and northwestern limb. The remnant is believed to be interacting with a molecular cloud and the harder emission to the south is explained as a result of increased absorption along the line-of-sight there. I argue that the softer emission comes from X-ray emitting material with an enhanced abundance of oxygen. For the second SNR, E0102.2 72.2, the spatial structure is investigated in detail using two-dimensional image fitting techniques. Evidence is found for a ring-like and a spherically symmetric shell-like component both of which were modeled as homogeneous regions. In addition, a significant fraction of the observed flux (approximately 11 percent) must come from a resolved clumped component. A comparison with optical and radio imagery is made to provide a physical basis for the components identified in the X-ray analysis. The mass of X-ray emitting gas in the remnant is estimated and a value of approximately 75 M(solar mass) was determined. The dominant uncertainty on this quantity is the extent of unresolved clumping in the X-ray gas. Such clumping would tend to reduce the mass estimate by f(exp 1/2), where f is the mean volume filling factor of the gas.

Hughes, John P.↗

NASA NTRS1993

High-resolution X-ray spectroscopy of the supernova remnant N132D

A joint nonequilibrium ionization analysis of spectral data from the Einstein Observatory of the SNR N132D in the LMC is presented on the basis of data from the Focal Plane Crystal Spectrometer (FPCS) and the Solid State Spectrometer (SSS), and lower spectral resolution data from the IPC and the Monitor Proportional Counter (MPC). The FPCS detected individual emission lines of O VII, O VIII, Ne IX, Ne X, Fe XVII, and possibly Fe XX. Measured line widths for the oxygen lines suggest Doppler broadening that is roughly consistent with optically measured expansion velocities of 2250 km/s. At the SSS/IPC temperature, FPCS flux ratios constrain the O/Fe abundance to be at least 1.9 times its solar value and the O/Ne abundance to be 0.2-1.0 times its solar value. Models for remnants with progenitor masses of 20 and 25 solar masses are completely consistent with the data, while remnants with progenitor masses of 13 and 15 solar masses can be made consistent if the progenitors are required to eject a large fraction of their iron cores.

Hwang, Una↗

NASA NTRS1993

Ginga observations of the Coma cluster and studies of the spatial distribution of iron

The large area counters on the Japanese satellite Ginga have been used to determine the X-ray spectrum from the central region of the Coma cluster of galaxies over the energy range from 1.5 to 20 keV. The spectrum is well represented by an isothermal model of temperature 8.21 +/- 0.16 keV and a heavy element (iron) abundance of 0.212 +/- 0.027, relative to the cosmic value. The Ginga spectrum was found to be consistent with the X-ray spectra from the Tenma and EXOSAT satellites for a large class of nonisothermal temperature distributions. The measured iron elemental abundances were used to set a lower limit on the total mass of iron in Coma under the assumption that the iron is not distributed uniformly throughout the cluster. The mass ratio of iron relative to hydrogen (within 2 Mpc) is not less than 18 percent of the cosmic iron to hydrogen mass ratio. This compares to an average abundance of 24 percent if the iron is distributed uniformly. We discuss these results in terms of models for the production of iron in galaxy clusters.

Hughes, John P.↗

NASA NTRS1993

An astrophysics data program investigation of spatial structure of supernova remnants

The final report on astrophysics data program investigation of spatial structure of supernova remnants for the period 1 Aug. 1989 to 31 Jul. 1991 is presented. The goal of the project was the study of the spatial structure of supernova remnants (SNR's) as observed in the x-ray band. A number of software tools were developed for the analysis: (1) a program to fit various geometric models to high resolution x-ray data, and (2) programs for Fourier Transform analysis of clumping in SNR's. These programs were applied to high resolution imager (HRI) data on the young galactic SNR's Tycho and Kepler with some success.

Hughes, John P.↗