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NASA NTRS2015

Constraining the Physics of AM Canum Venaticorum Systems with the Accretion Disk Instability Model

Recent work by Levitan et al. has expanded the long-term photometric database for AM CVn stars. In particular, their outburst properties are well correlated with orbital period and allow constraints to be placed on the secular mass transfer rate between secondary and primary if one adopts the disk instability model for the outbursts. We use the observed range of outbursting behavior for AM CVn systems as a function of orbital period to place a constraint on mass transfer rate versus orbital period. We infer a rate approximately 5 x 10(exp -9) solar mass yr(exp -1) ((P(sub orb)/1000 s)(exp -5.2)). We show that the functional form so obtained is consistent with the recurrence time-orbital period relation found by Levitan et al. using a simple theory for the recurrence time. Also, we predict that their steep dependence of outburst duration on orbital period will flatten considerably once the longer orbital period systems have more complete observations.

accretion↗

NASA NTRSDate not supplied

A Model for Ice Accretion Roughness Evolution and Spatial Variations

Over the past decade, multiple investigations of ice accretion roughness and spatial variations have been performed in the Icing Research Tunnel (IRT) at the NASA Glenn Research Center. The early investigations used models of NACA 0012 airfoils with different chord sizes and focused on temporal scaling and primary cloud scaling parameters such as stagnation point collection efficiency. Subsequent investigations included the effects of model sweep, airfoil shape, airfoil lifting condition, and freestream static temperature. To develop a predictive model for roughness evolution in generalized icing situations, the maximum roughness values for the airfoils and conditions used in the angle of attack and freestream temperature investigations were scaled to eliminate the temporal variations. LEWICE simulations were employed to identify the local collection efficiency at the locations of maximum roughness, and a two-dimensional panel-method code was used to identify the local static pressure at the location of the maximum roughness. Because of the stochastic nature of ice accretion roughness, a physics-directed approach was employed to develop a multi-dimensional correlation based on the local pressure coefficient, the local total temperature, the cloud properties, and the cloud exposure time. The resulting correlation predictions are compared to ice shapes measured in the IRT for both a 21-in. NACA 0012 airfoil model and a 60-in. HAARP-II model. The resulting predictions indicate that the local freezing fraction must be included in the roughness predictive model. Implications regarding icing heat transfer predictions using the resulting roughness model are also discussed.

Icing↗

NASA NTRS2016

Nustar Reveals the Extreme Properties of the Super-Eddington Accreting Supermassive Black Hole in PG 1247+267

PG1247+267 is one of the most luminous known quasars at z approximately 2 and is a strongly super-Eddington accreting supermassive black hole (SMBH) candidate. We obtained NuSTAR data of this intriguing source in December 2014 with the aim of studying its high-energy emission, leveraging the broad band covered by the new NuSTAR and the archival XMM-Newton data. Several measurements are in agreement with the super-Eddington scenario for PG1247+267: the soft power law (gamma = 2.3 +/- 0.1); the weak ionized Fe emission line; and a hint of the presence of outflowing ionized gas surrounding the SMBH. The presence of an extreme reflection component is instead at odds with the high accretion rate proposed for this quasar. This can be explained with three different scenarios; all of them are in good agreement with the existing data, but imply very different conclusions: i) a variable primary power law observed in a low state, superimposed on a reflection component echoing a past, higher flux state; ii) a power law continuum obscured by an ionized, Compton thick, partial covering absorber; and iii) a relativistic disk reflector in a lamp-post geometry, with low coronal height and high BH spin. The first model is able to explain the high reflection component in terms of variability. The second does not require any reflection to reproduce the hard emission, while a rather low high-energy cutoff of approximately 100 keV is detected for the first time in such a high redshift source. The third model require a face-on geometry, which may affect the SMBH mass and Eddington ratio measurements. Deeper X-ray broad-band data are required in order to distinguish between these possibilities.

accretion disks↗

NASA NTRS2002

Regimes of Pulsar Pair Formation and Particle Energetics

We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.

Harding, Alice K.↗

NASA NTRS2019

Ice-Crystal Icing Accretion Studies at the NASA Propulsion Systems Laboratory

This paper describes an ice-crystal icing experiment conducted at the NASA Propulsion System Laboratory during June 2018. This test produced ice shape data on an airfoil for different test conditions similar to those inside the compressor region of a turbo-fan jet engine. Mixed-phase icing conditions were generated by partially freezing out a water spray using the relative humidity of flow as the primary parameter to control freeze-out. The paper presents the ice shape data and associated conditions which include pressure, velocity, temperature, humidity, total water content, melt ratio, and particle size distribution. The test featured a new instrument traversing system which allowed surveys of the flow and cloud. The purpose of this work was to provide experimental ice shape data and associated conditions to help develop and validate ice-crystal icing accretion models. The results support previous experimental observations of a minimum melt-ratio threshold for accretion to occur as well as the existence of a plateau region where the icing severity is high for a range of melt ratios. However, a maximum limit for melt ratio, which is suggested in the ice crystal icing literature, was not observed perhaps complicated by the potential for some supercooling of the water at these conditions.

Engine Icing↗

DOE OSTI2024

Galaxies with biconical ionized structure in MaNGA – I. Sample selection and driven mechanisms

ABSTRACT Based on the integral field unit (IFU) data from Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we develop a new method to select galaxies with biconical ionized structures, building a sample of 142 edge-on biconical ionized galaxies. We classify these 142 galaxies into 81 star-forming galaxies, 31 composite galaxies, and 30 AGNs (consisting of 23 Seyferts and 7 LI(N)ERs) according to the [N ii]-BPT diagram. The star-forming bicones have bar-like structures while AGN bicones display hourglass structures, and composite bicones exhibit transitional morphologies between them due to both black hole and star formation activities. Star-forming bicones have intense star formation activities in their central regions, and the primary driver of biconical structures is the central star formation rate surface density. The lack of difference in the strength of central black hole activities (traced by dust attenuation corrected [O iii]λ5007 luminosity and Eddington ratio) between Seyfert bicones and their control samples can be naturally explained as that the accretion disc and the galactic disc are not necessarily coplanar. Additionally, the biconical galaxies with central LI(N)ER-like line ratios are edge-on disc galaxies that show strong central dust attenuation. The radial gradients of H α surface brightness follow the r−2.35 relation, roughly consistent with r−2 profile, which is expected in the case of photoionization by a central point-like source. These observations indicate obscured AGNs or AGN echoes as the primary drivers of biconical structures in LI(N)ERs.

Zhou, Zhi-Jie (ORCID:0000000317096005)↗

NASA NTRS1988

'Tertiary' nuclear burning - Neutron star deflagration?

A motivation is presented for the idea that dense nuclear matter can burn to a new class of stable particles. One of several possibilities is an 'octet' particle which is the 16 baryon extension of alpha particle, but now composed of a pair of each of the two nucleons, (3Sigma, Delta, and 2Xi). Such 'tertiary' nuclear burning (here 'primary' is H-He and 'secondary' is He-Fe) may lead to neutron star explosions rather than collapse to a black hole, analogous to some Type I supernovae models wherein accreting white dwarfs are pushed over the Chandrasekhar mass limit but explode rather than collapse to form neutron stars. Such explosions could possibly give gamma-ray bursts and power quasars, with efficient particle acceleration in the resultant relativistic shocks. The new stable particles themselves could possibly be the sought-after weakly interacting, massive particles (WIMPs) or 'dark' matter.

Michel, F. Curtis↗

NASA NTRS1991

Regular variability of the shape of the primary minimum of the orbital light curve of SS 433 with the phase of the precessional period

The regular variations of the shape of the primary minimum of the orbital 13.082-day light curve of SS 433 with the phase of the 162.5-day processional period were discovered by analysis of the photometrical databank. The regular variability of the shape of the primary minimum of the discovered light curve of SS 433 reflects displacement with the 26-day double orbital period of at least two hot bright spots on the surface of the processional accretional disk and their eclipse by a normal star. Other aspects of the investigation are further discussed.

Cherepashchuk, A. M.↗

NASA NTRS2001

A Study of Ice Accretion Physics to Improve the Ice Accretion on Airfoils

This three-year grant began on November 7, 1996 and was no-cost extended to end on October 30, 2000. The objectives of the grant were: (1) To examine the effect of wind tunnel turbulence on ice accretion; (2) To determine the relationship between ice accretion geometry and airfoil performance; and (3) To determine if the wake-survey method was an appropriate experimental technique for iced-airfoil drag measurement. As specified in the grant the primary deliverables for this research were annual reports in the form of AIAA papers presented at national meetings each year. Masters theses and annual oral reports to be given at NASA Lewis (now Glenn) were also deliverables. Six AIAA papers documented the research findings from this study, Mr. Chad Henze's Masters thesis describes the wind tunnel turbulence work in detail, and a summary of the icing wind tunnel turbulence work was published in the archival AIAA Journal of Aircraft. A brief summary of the findings is given. Please refer to the reports for the details of the studies and findings.

Bragg, Michael B.↗

NASA NTRS2001

The Spectral Energy Distribution of the Seyfert Galaxy Ton S180

We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the source, combining simultaneous Chandra, ASCA and EUVE data with contemporaneous FUSE, HST, and ground-based optical and infrared data. The resulting SED shows that most of the, energy is emitted in the 10 - 100 eV regime, which must be dominated by the primary energy source. No spectral turnover is evident in the UV regime. This, the strong soft X-ray emission, and the overall shape of the SED indicate that emission from the accretion disk peaks between 15 and 100 eV. High resolution FUSE spectra showing UV absorption due to OVI and the lack of detectable X-ray absorption in the Candra spectrum demonstrate the presence of a low column density of highly ionized gas along our line of sight.

Turner, T. J.↗

NASA NTRS1984

The 1982 eclipse of 31 Cygni

UBV photometry and optical-UV spectroscopy of the primary eclipse of the long period Zeta Aurigae-like system 31 Cygni are reported. The precise timings made possible by the photometry imply that the spectral features could be due to an accretion shock associated with a hot star embedded in an extended chromosphere surrounding the red supergiant. The data also suggest an extended clumpy structure to the atmosphere of the late-type supergiant in the binary.

Hopkins, J. L.↗

NASA NTRS1996

X-Ray spectroscopy of cooling flows

Cooling flows in clusters of galaxies occur when the cooling time of the gas is shorter than the age of the cluster; material cools and falls to the center of the cluster potential. Evidence for short X-ray cooling times comes from imaging studies of clusters and X-ray spectroscopy of a few bright clusters. Because the mass accretion rate can be high (a few 100 solar mass units/year) the mass of material accumulated over the lifetime of a cluster can be as high as 10(exp 12) solar mass units. However, there is little evidence for this material at other wavelengths, and the final fate of the accretion material is unknown. X-ray spectra obtained with the Einstein SSS show evidence for absorption; if confirmed this result would imply that the accretion material is in the form of cool dense clouds. However ice on the SSS make these data difficult to interpret. We obtained ASCA spectra of the cooling flow cluster Abell 85. Our primary goals were to search for multi-temperature components that may be indicative of cool gas; search for temperature gradients across the cluster; and look for excess absorption in the cooling region.

Prestwich, Andrea↗

NASA NTRS1998

Variability Analysis and the Structure of Active Galactic Nuclei

This five-year Long-Term Space Astrophysics grant provided the support for several major steps in advancing our knowledge of the internal structure of active galactic nuclei. The single largest portion of this program had to do with the development and application of techniques for "reverberation mapping", the use of spectral monitoring of several different bands related by radiation reprocessing to infer the internal geometry of sources. Major steps were taken in this regard, particularly in establishing the distribution in radius of emission line material, and in relating the apparent reprocessing of continuum bands to the underlying structure of the accretion disk. Another major effort built directly upon these results. Once the case for continuum reprocessing was made by the monitoring, it next behooved us to understand the spectral output of AGN as a result of this reprocessing. As a result, our view of continuum production in AGN is now much better focussed on the key problems. A third focus of effort had to do with the nature of X-ray variability in AGN, and what it can tell us about the dynamics of extremely hot material in the immediate outskirts of the supermassive black holes that form the central engines of active galactic nuclei. In addition to these primary efforts, this grant also supported many other, smaller projects. Several of these were demonstrations of how the material spewed out of AGN in relativistic.ets generate the radiation by which we observe them. J Finally, the portion of this study that had to do with continuum production by accretion disks in AGN led naturally to several papers in which new developments were presented having to do with "advection-dominated accretion disks", those disks in which accretion appears to proceed at a substantial rate, but in which radiation processes are weak.

Krolik, Julian H.↗

NASA NTRS1998

Variability Analysis and the Structure of Active Galactic Nuclei

This five-year Long-Term Space Astrophysics grant provided the support for several major steps in advancing our knowledge of the internal structure of active galactic nuclei. The single largest portion of this program had to do with the development and application of techniques for 'reverberation mapping, the use of spectral monitoring of several different bands related by radiation reprocessing to infer the internal geometry of sources. Major steps were taken in d-ds regard, particularly in establishing the distribution in radius of emission line material, and in relating the apparent reprocessing of continuum bands to the underlying structure of the accretion disk. Another major effort built directly upon these results. Once the case for continuum reprocessing was made by the monitoring, it next behooved us to understand the spectral output of AGN as a result of this reprocessing. As a result, our view of continuum production in AGN is now much better focussed on the key problems. A third focus of effort had to do with the nature of X-ray variability in AGN, and what it can tell us about the dynamics of extremely hot material in the immediate outskirts of the supermassive black holes that form the central engines of active galactic nuclei. In addition to these primary efforts, this grant also supported many other, smaller projects. Several of these were demonstrations of how the material spewed out of AGN in relativistic jets generate the radiation by which we observe them. Finally, the portion of this study that had to do with continuum production by accretion disks in AGN led naturally to several papers in which new developments were presented having to do with 'advection-dominated accretion disks', those disks in which accretion appears to proceed at a substantial rate, but in which radiation processes are weak.

Krolik, Julian H.↗

NASA NTRS1991

X-ray echoes from gamma-ray bursts

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed.

Dermer, Charles D.↗

NASA NTRS1991

High energy neutrinos from primary cosmic rays accelerated in the cores of active galaxies

The spectra and high-energy neutrino fluxes are calculated from photomeson production in active galactic nuclei (AGN) such as quasars and Seyfert galaxies using recent UV and X-ray observations to define the photon fields and an accretion-disk shock-acceleration model for producing ultrahigh-energy cosmic rays in the AGN. Collectively AGN should produce the dominant isotropic neutrino background between 10 exp 4 and 10 exp 10 GeV. Measurement of this background could be critical in determining the energy-generation mechanism, evolution, and distribution of AGN. High-energy background spectra and spectra from bright AGN such as NGC4151 and 3C273 are predicted which should be observable with present detectors. High energy AGN nus should produce a sphere of stellar disruption around their cores which could explain their observed broad-line emission regions.

Stecker, F. W.↗

NASA NTRS2013

On the Nature of the mHz X-ray Quasi-Periodic Oscillations from Ultraluminous X-ray source M82 X−1: Search for Timing-Spectral Correlations

Using all the archival XMM-Newton X-ray (3-10 keV) observations of the ultraluminous X-ray source (ULX) M82 X−1, we searched for a correlation between its variable mHz quasi-periodic oscillation (QPO) frequency and its hardness ratio (5-10 keV/3-5 keV), an indicator of the energy spectral power-law index. When stellar-mass black holes (StMBHs) exhibit type-C low-frequency QPOs (∼0.2-15 Hz), the centroid frequency of the QPO is known to correlate with the energy spectral index. The detection of such a correlation would strengthen the identification of M82 X−1's mHz QPOs as type-C and enable a more reliable mass estimate by scaling its QPO frequencies to those of type-C QPOs in StMBHs of known mass.We resolved the count rates and the hardness ratios of M82 X−1 and a nearby bright ULX (source 5/X42.3+59) through surface brightness modeling.We detected QPOs in the frequency range of 36-210 mHz during which M82 X−1's hardness ratio varied from 0.42 to 0.47. Our primary results are (1) that we do not detect any correlation between the mHz QPO frequency and the hardness ratio (a substitute for the energy spectral power-law index) and (2) similar to some accreting X-ray binaries, we find that M82 X−1's mHz QPO frequency increases with its X-ray count rate (Pearson's correlation coefficient = +0.97). The apparent lack of a correlation between the QPO centroid frequency and the hardness ratio poses a challenge to the earlier claims that the mHz QPOs of M82 X−1 are the analogs of the type-C low-frequency QPOs of StMBHs. On the other hand, it is possible that the observed relation between the hardness ratio and the QPO frequency represents the saturated portion of the correlation seen in type-C QPOs of StMBHs-in which case M82 X−1's mHz QPOs can still be analogous to type-C QPOs.

Nature↗

NASA NTRS1985

On the evolution of accretion disc flow in cataclysmic variables. III - Outburst properties of constant and uniform-alpha model discs

Attention is given to the stability and evolution of some simple accretion disk models in which the viscosity is prescribed by an ad hoc, uniform-alpha model. Emphasis is placed on systems in which the mass input rate from the secondary to the disk around the primary is assumed to be constant, although initial calculations with variable mass input rates are also performed. Time-dependent visual magnitude light curves constructed for cataclysmic binaries with a range of disk size, primary mass and mass input rate, and viscosity magnitude, are compared with the observed properties of various cataclysmic variable subclasses. The results obtained indicate that the observational differences between novae and dwarf novae may be due to mass input rate differences. The present models can reproduce the gross observational features of U-Gem-type dwarf nova outbursts.

Lin, D. N. C.↗