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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 541 records · Page 30
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NASA NTRS1995

The dim inner accretion disk of the quiescent black hole A0620-00

We observed the X-ray nova A0620-00 with the Hubble Space Telescope (HST) Faint object Spectrograph 16 yr after its 1975 outburst. We present a single spectrum (1250-4750 A), which is approximately an average over a full 7.8 hr orbital cycle of the source. The continuum can be fitted approximately by a blackbody model with T = 9000 K and a small projected source area, which is approximately 1 % of the expected area of the accretion disk. AS0620-00 is faint in the far-UV band; its luminosity is comparable to the luminosity of the quiescent dwarf-nova accretion disk (i.e., excluding the white dwarf). By analogy with dwarf novae, the optical luminosity of the disk (M(sub nu) approximately = 7) and the orbital period of A0620-00 imply that the rate of mass transfer onto the outer disk in M(sub d) approximately 10(exp -10) solar mass/yr. We also observed A0620-00 with the ROSAT PSPC X-ray detector for 3 x 10(exp 4) s and detected a faint source (5 sigma) at the location of the X-ray nova. For an assumed blackbody spectrum the source temperature and luminosity are approximately 0.16 keV and 6 x 10(exp 30) ergs/s, respectively (d = 1 kpc). This luminosity implies that the rate of mass transfer into the black hole is extraordinarily small: M(sub BH) less than 5 x 10(exp -15) solar mass/yr. The much larger mass transfer rate onto the outer disk, and the UV/X-ray faintness of the inner disk confirm key predictions of the disk instability model for the nova outburst of A0620-00 published by Huang and Wheeler and by Mineshige and Wheeler.

Mcclintock, Jeffrey E.↗
NASA NTRS1995

RX J0045.4+4154: A recurrent supersoft x-ray transient in M31

Using data extracted from the ROSAT archive we have discovered a recurrent supersoft X-ray transient RX J0045.4+4154 in M31. The first outburst began on 1992 February 2 and continued for at least 4 days, until the end of the observation sequence. A second outburst that lasted more than 6 days was seen to begin on 1993 January 7. The X-ray spectrum on both occasions yields a characteristic blackbody temperature of approximately 90 eV. For a range of plausible continuum models, the hydrogen column density is (0.8-1.5) x 10(exp 21)/sq cm and is consistent with the source being located in M31. This implies an unabsorbed 0.1-2.0 keV peak luminosity of approximately 10(exp 38) ergs/sec. This is the first recurrent X-ray transient to be found in M31 and is particularly notable because it is much softer than the bright X-ray transients seen in our Galaxy. The spectrum is characteristic of the supersoft class of X-ray sources, which are thought to be accreting white dwarfs that have a hydrogen-burning surface layer. A fit to a white dwarf model atmosphere gives a temperature of 10(exp 6)K, the hottest found so far. This high temperature is consistent with a white dwarf mass of 1.3-1.4 solar mass, approaching the Chandrasekhar limit, and burning close to the nuclear stability limit.

White, N. E.↗
NASA NTRS1995

Evolution of the symbiotic binary system AG Dranconis

We present an analysis of new and archival photometric and spectroscopic observations of the symbiotic star AG Draconis. This binary has undergone several 1 - 3 mag optical and ultraviolet eruptions during the past 15 years. Our combination of optical and ultraviolet spectroscopic data allow a more complete analysis of this system than in previous papers. AG Dra is composed of a K-type bright giant M(sub g) approximately 1.5 solar mass) and a hot, compact star M(sub h approximatelly 0.4 - 0.6 solar mass) embedded in a dense, low metallicity nebula. The hot component undergoes occasional thermonuclear runaways that produce 2 - 3 mag optical/ultraviolet eruptions. During these eruptions, the hot component develops a low velocity wind that quenches x-ray emission from the underlying hot white dwarf. The photoionized nebula changes its volume by a factor of 5 throughout an eruptin cycle. The K bright giant occults low ionization emission lines during superior conjunctions at all outburst phases but does not occult high ionization lines in outburst (and perhaps quiescence). This geometry and the component masses suggest a system inclination of i approximately 30 deg - 45 deg.

Mikolajewska, Joanna↗
NASA NTRS1996

Research activities in nuclear astrophysics and related areas

NASA/GRO grant NAG 5-2081, at the University of Chicago, has provided support for a broad program of theoretical research in nuclear astrophysics and related areas, with regard to gamma-ray and hard X-ray emission from classical nova explosions. This research emphasized the possible detection of 22Na gamma-ray line emission from nearby novae involving ONeMg white dwarfs, the detailed examination of 26Al production in novae, and the possible detection of the predicted early gamma ray emission from novae that arises from the decay of the short lived, positron emitting isotopes of CNO elements. Studies of nova related problems have consumed an increasing fraction of the Principal Investigator's research efforts over the past decade. Current research addresses problems associated with the standard model for the outbursts of the classical novae: the occurrence of thermonuclear runaways (TNR) in the accreted hydrogen rich envelopes on white dwarfs in close binary systems (see, e.g., the reviews by Truran 1982; and Shara 1989). Research in progress and planned for the next three years has three main objectives: (1) to gain an improved understanding of the early evolution of the light curves of, particularly, the fastest novae; (2) to gain an improved understanding of the relative importance of the various possible mechanisms of envelope hydrogen depletion (e.g. winds, common envelope driven mass loss, and nuclear burning) to the long term evolution of novae in outburst; and (3) to seek to provide a somewhat more definitive statement of the role of classical novae in nucleosynthesis. Our proposed 2-D studies of convection during the early phases of the TNR and our systematic attempt to incorporate an improved treatment of radiation hydrodynamics into the hydrodynamic code utilized in our calculations, are particularly relevant to the first of these objectives. Further 2-D studies of the effects of common envelope evolution are intended to provide more realistic constraints on the mass depletion mechanisms. Finally, detailed calculations of the thermonuclear history of the matter ejected in novae will be carried out for representative nova configurations involving both carbon-oxygen (CO) and oxygen-neon-magnesium (ONeMg) white dwarfs.

Source record↗
NASA NTRS1995

Nonlinear Waves in Magnetized Accretion Disks

Time-dependent accretion for a magnetized disk can exhibit short timescale outbursts of high-power jets associated with bursts of disk radiation. The burst of energy in jets can produce outward propagating disturbances in preexisting (+/- z) jet flows. the disturbances are strong and can be expected to steepen and form strong shock waves. The strong linear polarization (up to approximately 30%) and large polarization position angle changes (90 deg and more) seen in the optical outbursts of some quasars clearly indicate synchrotron radiation, and this component of the radiation is probably associated with the burst in jet energy in the present model.

Lovelace, R. V. E.↗
NASA NTRS1997

Gamma Rays from Classical Novae

NASA at the University of Chicago, provided support for a program of theoretical research into the nature of the thermonuclear outbursts of the classical novae and their implications for gamma ray astronomy. In particular, problems which have been addressed include the role of convection in the earliest stages of nova runaway, the influence of opacity on the characteristics of novae, and the nucleosynthesis expected to accompany nova outbursts on massive Oxygen-Neon-Magnesium (ONeMg) white dwarfs. In the following report, I will identify several critical projects on which considerable progress has been achieved and provide brief summaries of the results obtained:(1) two dimensional simulation of nova runaway; (2) nucleosynthesis of nova modeling; and (3) a quasi-analytic study of nucleosynthesis in ONeMg novae.

Source record↗
NASA NTRS1998

Identification of the Periodic Hard X-Ray Transient GRO J1849-03 with the X-Ray Pulsar GS 1843-02 = X1845-024: A New Be/X-Ray Binary

We identify the periodic transient hard X-ray source GRO J1849-03 with the transient x-ray pulsar GS 1843-02 = X1845-024 based on the detection of x-ray outbursts from X1845-024 coincident with hard x-ray outbursts of GRO J1849-03. Based on its spin period of 94.8 s and its orbital period of 241 days, we classify the system as a Be/X-ray binary.

Soffitta, P.↗
NASA NTRS1997

Discovery and Orbital Determination of the Transient X-Ray Pulsar GRO J1750-27

We report on the discovery and hard X-ray (20 - 70 keV) observations of the 4.45 s period transient X-ray pulsar GRO J1750-27 with the BATSE all-sky monitor on board CGRO. A relatively faint out- burst (less than 30 mcrab peak) lasting at least 60 days was observed during which the spin-up rate peaked at 38 pHz/s and was correlated with the pulsed intensity. An orbit with a period of 29.8 days was found. The large spin-up rate, spin period, and orbital period together suggest that accretion is occurring from a disk and that the outburst is a "giant" outburst typical of a Be/X-ray transient system. No optical counterpart has yet been reported.

Scott, D. M.↗
NASA NTRS1996

Io's Volcanism: Thermo-Physical Models of Silicate Lava Compared with Observations of Thermal Emission

Analyses of thermal infrared outbursts from the jovian satellite Io indicate that at least some of these volcanic events are due to silicate lava. Analysis of the January 9, 1990 outburst indicates that this was an active eruption consisting of a large lava flow (with mass eruption rate of order 10(exp 5) cubic m/sec) and a sustained area at silicate liquidus temperatures. This is interpreted as a series of fire fountains along a rift zone. A possible alternative scenario is that of an overflowing lava lake with extensive fire fountaining. The January 9, 1990 event is unique as multispectral observations with respect to time were obtained. In this paper, a model is presented for the thermal energy lost by active and cooling silicate lava flows and lakes on Io. The model thermal emission is compared with Earth-based observations and Voyager IRIS data. The model (a) provides an explanation of the thermal anomalies on Io's surface; (b) provides constraints on flow behavior and extent and infers some flow parameters; and (c) determines flow geometry and change in flow size with time, and the temperature of each part of the flow or lava lake surface as a function of its age. Models of heat output from active lava flows or inactive but recently emplaced lava flows or overturning lava lakes alone are unable to reproduce the observations. If the January 9, 1990 event is the emplacement of a lava flow, the equivalent of 27 such events per year would yield a volume of material sufficient, if uniformly distributed, to resurface all of Io at a rate of 1 cm/year.

Davies, Ashely G.↗
NASA NTRS2000

X-Ray Dips In Black Hole Candidates

A total of 52 Rossi Timing Explorer (RXTE) observations of the black hole candidate 4UI630-47 were carried out during the source's bright outburst during 1998. After the data tapes arrived in August 1998, we began analyzing these data to characterize the spectral and timing behavior of the source. A preliminary report on our analysis of the data was at the Second Workshop on Relativistic Jet Sources in the Galaxy. held in Paris presented in December 1998. The most interesting result from this analysis is the discovery of quasi- periodic oscillations (QPOs) at frequencies varying from 3 Hz to 0.1 Hz during the latter part of the outburst. The QPOs turn on abruptly and simultaneously with a sharp change in the x-ray spectrum. The results have been published in the Astrophysical Journal. This work formed a major part of the Ph.D. thesis of John Tomsick, who received his Ph.D. in Physics at Columbia University in the summer of 1999 and subsequently received a postdoctoral fellowship at the University of California, San Diego.

Kaaret, P.↗
NASA NTRS2001

Multiwavelength Modeling of Nove Atmospheres

LMC 1988 #1 was a slow, CO type, dust forming classical nova. It was the first extragalactic nova to be observed with the IUE satellite. We have successfully fitted observed ultraviolet and optical spectra of LMC 1988 #1 taken within the first two months of its outburst (when the atmosphere was still optically thick) with synthetic spectra computed using PHOENIX nova model atmospheres. The synthetic spectra reproduce most of the features seen in the spectra and provide V band magnitudes consistent with the observed light curve. The fits are improved by increasing the CNO abundances to 10 times the solar values. The bolometric luminosity of LMC 1988 #1 was approximately constant at 2 x 10(exp 38) ergs per second at a distance of 47.3 kpc for the first 2 months of the outburst until the formation of the dust shell.

Huschildt, P. H.↗
NASA NTRS2002

Studying X-Ray Binaries with High Energy Frequency Quasi-Periodic Oscillations

The goal of this investigation is to further our understanding of the dynamics of secreting neutron stars and black holes in the hope of using these systems as probes of the physics of strong gravitational fetus. The main focus of this work has been a multi-year program of simultaneous millisecond X-ray timing and spectral observations carried out with the Rossi X-Ray Timing Explorer (RXTE) to perform the X-ray timing and one of the satellites Asca, BeppoSAX, or Chandra to perform X-ray spectral measurements. With the advent of Chandra, we have extended our work to incLude extragalactic X-ray binaries. We conducted a comprehensive study of the X-ray and radio behavior of the Black Hole Candidate (BHC) X-ray transient XTE J1550-564 using RXTE, Chandra, and the Australian Telescope Compact Array (ATCA). We showed that strong radio emission is associated with major X-ray outbursts involving an X-ray state transition, while a compact radio jet is seen in the low/hard X-ray state found in the outburst decay. Interesting, the total energy required to produce the compact jet may be a substantial fraction of the total accretion energy of the system in that state. We also performed a detailed study of the spectral and timing properties of the decay. In joint RXTE/BeppoSAX observations of the neutron-star X-ray binary Cyg X-2, we discovered a correlation between the timing properties (the frequency of the horizontal branch oscillations) and the properties of a soft, thermal component of the X-ray spectrum. d e showed that more det<iiled measurements of this source may lead to constraints on models of the accretion flow and the emission of X- ray from accreting neutron stars. We have completed analysis of RXTE observations of the X-ray transient SAX J1750.8-2900 made after detection of X-ray bursts from the source with the BeppoSAX Wide-Field Camera. We discovered millisecond oscillations in both the persistent emission and in the X-ray bursts.

Kaaret, P.↗
NASA NTRS2002

Studies of Transient Meteor Activity

Meteoroids bombard Earth's atmosphere daily, but occasionally meteor rates increase to unusual high levels when Earth crosses the relatively fresh ejecta of comets. These transient events in meteor activity provide clues about the whereabouts of Earth-threatening long-period comets, the mechanisms of large-grain dust ejection from comets, and the particle composition and size distribution of the cometary ejecta. Observations of these transient events provide important insight in natural processes that determine the large grain dust environment of comets, in natural phenomena that were prevalent during the time of the origin of life, and in processes that determine the hazard of civilizations to large impacts and of man-made satellites to the periodic blizzard of small meteoroids. In this proposal, three tasks form a coherent program aimed at elucidating various aspects of meteor outbursts, with special reference to planetary astronomy and astrobiology. Task 1 was a ground-based effort to observe periods of transient meteor activity. This includes: (1) stereoscopic imaging of meteors during transient meteor events for measurements of particle size distribution, meteoroid orbital dispersions and fluxes; and (2) technical support for Global-MS-Net, a network of amateur-operated automatic counting stations for meteor reflections from commercial VHF radio and TV broadcasting stations, keeping a 24h vigil on the level of meteor activity for the detection of new meteor streams. Task 2 consisted of ground-based and satellite born spectroscopic observations of meteors and meteor trains during transient meteor events for measurements of elemental composition, the presence of organic matter in the meteoroids, and products generated by the interaction of the meteoroid with the atmosphere. Task 3 was an airborne effort to explore the 2000 Leonid meteor outbursts, which are anticipated to be the most significant of transient meteor activity events in the remainder of the agreement period. This includes technical support for a multi-instrument aircraft campaign, Leonid MAC.

Jenniskens, Peter M. M.↗
NASA NTRS2002

XTE J1946+274: An Enigmatic X-Ray Pulsar

XTE J1946+274 = GRO J1944+26 is a 15.8-s X-ray pulsar discovered simultaneously by the Rossi X-ray Timing Explorer (RXTE) and the Burst and Transient Source Experiment (BATSE) in September 1998. Follow-up optical/IR observations resulted in the discovery of a Be star companion. Our pulse timing analysis of BATSE and RXTE data indicates that the orbital period is approximately 169 days. Since its discovery in 1998, XTE J1946+274 has undergone 13 outbursts. These outbursts axe not regularly spaced. They occur approximately twice per orbit and are not locked in orbital phase, unlike most Be/X-ray transient systems. A possible explanation for this is a global-one armed oscillation or density perturbation propagating rapidly in the Be star's disk. We will investigate radial velocity variations in the central peak of the H-alpha line to look for evidence of such a perturbation. From 2001 March-September, we regularly monitored XTE J1946+274 with the RXTE PCA. We will demonstrate that the spectrum appears to be varying with orbital phase, based on the 2001 and 1998 RXTE PCA observations. We will also present histories of pulsed frequency and flux.

Wilson, Colleen A.↗
NASA NTRS1998

Comparison of the X-Ray and Radio Light Curves of Quasar PKS 1510--089

We present results for the X-ray-bright superluminal AGN PKS 1510-089 (z=0.36) monitored weekly with the Rossi X-Ray Timing Explorer for the past four years in order to study the origin of X-ray emission from this extremely variable blazer. These RXTE data are compared with weekly cm-band flux and polarization observations from the Michigan Diameter telescope, to identify correlated activity and associated frequency-dependent time delays for constraining X-ray emission models; and bimonthly 7mm VLBA total and linearly polarized intensity imaging to identify temporal associations between X-ray events and the ejection of superluminal components and disturbances in the magnetic field, to test if the X-ray energy release is related to changes in the inner jet flow. Both the X-ray (2-20 keV) and radio flux are highly variable on timescales of weeks. The VLBA mas structure is dominated by a bright core with a weak jet; both the ejection of very fast superluminal knots and changes in the fractional polarization and EVPA of the core on timescales of one to four months are identified. Two outbursts in 1997 are well-resolved in both the centimeter and X-ray bands. Both the strong temporal association and the similar outburst shape support a causal relation, and a discrete cross-correlation analysis identifies that the X-ray lags the radio by 16 days during the bursts. Starting in 1998 the behavior changes: the correlation is weaker with the X-ray possibly leading the radio by six days. During the full time window there is a correlation between bands as expected if the radio photons are upscattered to X-ray energies. The time correlations and difference between the flat X-ray spectral index (0.0 <= alpha <= 0.5 where F(sub v) is proportional to v(exp -alpha)), and the mm-wave synchrotron spectrum (alpha = 0.8) are discussed within the framework of viable SSC models.

Aller, M. F.↗
NASA NTRS2002

Characteristics of Transients in the Galactic Bulge

Biweekly X-ray observations of the Galactic Bulge with the Rossi X-Ray Timing Explorer Proportional Counter Array for 5 years have built up statistics for different kinds of source behavior for low-mass binaries with neutron stars. The relation between the characteristic behaviors is not known. A typical transient may rise fast and decay exponentially in brightness and repeat this cycle after short (1/2 yr) or long intervals (20 yr). But an X-ray source also may be steady for an extended period (years) before the disk can become quiescent. It fades in the same way as do the transients which immediately decay. These sources have been reported to be very cool in quiescence; either not substantially heated by outbursts, or cooled very quickly. There are 3 sources active during the last 5 years which were long lasting transients which turned off and 1 which turned on. We will compare their X-ray characteristics in outburst, and in so far as available with Chandra, in quiescence.

Swank, Jean H.↗
NASA NTRS2004

Low-mass X-ray Binaries with RXTE

Below are the publications which directly and indirectly evolved from this very successful program: 1) 'Search for millisecond periodicities in type I X-ray bursts of the Rapid Burster'; 2) 'High-Frequency QPOs in the 2000 Outburst of the Galactic Microquasar XTE J1550-564'; 3) 'Chandra and RXTE Spectroscopy of Galactic Microquasar XTE 51550-564 in Outburst'; 4) 'GX 339-4: back to life'; 5) 'Evidence for black hole spin in GX 339-4: XMM-Newton EPIC-PN and RXTE spectroscopy of the very high state'.

Source record↗
NASA NTRS2000

Evidence for Doppler-Shifted Iron Emission Lines in Black Hole Candidate 4U 1630-47

We report the first detection of a pair of correlated the X-ray spectrum of black hole candidate 4U 1630-47 outburst, based on Rossi X-Ray Timing Explorer (RXTE) emission lines in during its 1996 observations of the source. At the peak plateau of the outburst, the emission lines are detected, centered mostly at approx. 5.7 and approx. 7.7 keV, respectively, while the line energies exhibit random variability approx. 5%. Interestingly, the lines move in a concerted manner to keep their separation roughly constant. The lines also vary greatly in strength, but with the lower energy line always much stronger than the higher energy one. The measured equivalent width ranges from approx. 50 to approx. 270 eV for the former, and from insignificant detection to approx. 140 eV for the latter; the two are reasonably correlated. The correlation between the lines implies a causal connection; perhaps they share a common origin. Both lines may arise from a single K & alpha; line of highly ionized iron that is Doppler shifted either in a Keplerian accretion disk or in a bipolar outflow or even both. In both scenarios, a change in the line energy might simply reflect a change in the ionization state of line-emitting matter. We discuss the implication of the results and also raise some questions about such interpretations.

Cui, Wei↗