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NASA NTRS2000

Initial OSSE Sky Survey Observation: Deep Survey in the Virgo Region

The OSSE Virgo survey covered about 1% of the sky, using eight weeks of observing time on the Compton Gamma Ray Observatory, and was performed in conjunction with the EGRET and COMPTEL instruments on CGRO. A fundamental aspect of the survey was the development of data reduction techniques for the scanning data from the OSSE detectors. A direct algebraic approach for spatially deconvolving the data was developed. For the survey work, no background observations isolated from the survey region were acquired, unlike normal discrete source observations. The survey, reduction method covers the mapped region with a grid of pixels, and estimates the flux from each pixel by least-squares agreement with the data, assuming positivity constraints. This technique has led to the detection of compact sources at hard X-ray energies within the Virgo region, and the OSSE survey studies have been extended to the south galactic pole and north Ecliptic pole, with similar analysis techniques.

Cameron, Robert↗

NASA NTRS2012

Pulsar Emission Geometry and Accelerating Field Strength

The high-quality Fermi LAT observations of gamma-ray pulsars have opened a new window to understanding the generation mechanisms of high-energy emission from these systems, The high statistics allow for careful modeling of the light curve features as well as for phase resolved spectral modeling. We modeled the LAT light curves of the Vela and CTA I pulsars with simulated high-energy light curves generated from geometrical representations of the outer gap and slot gap emission models. within the vacuum retarded dipole and force-free fields. A Markov Chain Monte Carlo maximum likelihood method was used to explore the phase space of the magnetic inclination angle, viewing angle. maximum emission radius, and gap width. We also used the measured spectral cutoff energies to estimate the accelerating parallel electric field dependence on radius. under the assumptions that the high-energy emission is dominated by curvature radiation and the geometry (radius of emission and minimum radius of curvature of the magnetic field lines) is determined by the best fitting light curves for each model. We find that light curves from the vacuum field more closely match the observed light curves and multiwavelength constraints, and that the calculated parallel electric field can place additional constraints on the emission geometry

DeCesar, Megan E.↗

NASA NTRSDate not supplied

Brief Overview of Subsonic Single Aft Engine (SUSAN) Transport Aircraft Concept and Trade Space Exploration

The SUSAN concept uses a 20-megawatt Electrified Aircraft Propulsion system to enable advance Propulsion Airframe Integration in transport category aircraft. Alternative fuels will be used to reduce the amount of emissions per energy used. By combining these features there is the potential to reduce aircraft emissions by 50 percent per passenger/mile while retaining the size, speed, and range of large regional jets. The SUSAN is has a 750-mile economic mission, a 2500-mile design range and a maximum capacity of 180 passengers. The SUSAN configuration utilizes a single aft mounted engine and distributed electric wing-mounted thrusters on a tube and wing arrangement with a T-tail empennage. The SUSAN Electrofan employs a hybrid powertrain to enable: single turbofan operation on a large transport category aircraft; increased aerodynamic and propulsive efficiency through placement of electric engines; optimized turbofan sizing and efficiency through control and electric boosting, reduced control surface sizing through thrust augmentation. A single use battery is employed as the power source in case of turbofan failure. The design study also considers the constraints of operating within the current airport, airspace, and economic constraints. Forward work includes optimizing the overall aircraft configuration and including certain hard to model features like boundary layer ingestion or natural laminar flow across all appliable subsystems. Additional work forward work is a more extensive analysis of the configuration using alternative fuels.

Ralph Jansen↗

NASA NTRS2021

Potential origin of the state-dependent hard tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL

Context.0.1–10 MeV observations of the black hole microquasar Cygnus X-1 have shown the presence of a spectral feature in the form of a power law in addition to the standard black body (0.1–10 keV) and Comptontonization (10–200 keV) components usually seen in all black hole X-ray binaries. This so-called “high-energy tail” has recently been shown to be strong in the hard spectral state and has been interpreted as high-energy part of the emission from a compact jet. Aims. This result was, however, obtained from a data set largely dominated by hard state observations. In the soft state, only upper limits on the presence and hence the potential parameters of a hard tail could be derived. Using an extended data set we aim at obtaining better constraints on the properties of this spectral component in both states. Methods. We make use of data obtained from about 15 years of observations with the INTEGRAL satellite. The data set is separated into the different states and we analyse stacked state-resolved spectra obtained from both the gamma-ray Imager and the Spectrometer onboard. Results. A high-energy component is detected in both states, confirming its earlier detection in the hard state and its suspected presence in the soft state as seen in a much smaller SPI data set. We first characterize the hard tail components in the two states through a model-independent, phenomenological analysis. We then apply physical models based on hybrid Comptonization (eqpair and belm). The spectra are well modeled in all cases, with a similar goodness of the fit. The spectral properties of the tails in the two states are, however, quite different. This might indicate that the emission originates from different media in the two cases. Our results are compatible with a compact jet origin in the hard state and hybrid Comptonization in the soft state.

F. Cangemi↗

NASA NTRS1984

Fast variations in high-energy X-rays from solar flares and their constraints on nonthermal models

The results of a quantitatve analysis of quantitative the temporal properties of over 7000 hard X-ray solar flares are presented. The data were obtained with the Hard X-ray Burst Spectrometer of the SMM satellite. The data reveal examples of hundreds of fast spikes with durations of less than 1 s. The spectra of a well-observed fast spike were compared with the predicted spectra of a detailed nonthermal electron beam model, in order to determine upper limits for electron beam parameters and path lengths. The theoretical spectra were found to be consistent with the observed spectra when the separation of between the accretion site and the thick target was greater than 10 to the 8th cm. It is shown that if the separation is much greater than 3 x 10 to the 9th cm, the electrons with high pitch angles (greater than 60 deg) are either not emitted or are mirrored before they reach the footpoints.

Kiplinger, A. L.↗

NASA NTRS1992

Experiments with a decision-theoretic scheduler

This paper describes DTS, a decision-theoretic scheduler designed to employ state-of-the-art probabilistic inference technology to speed the search for efficient solutions to constraint-satisfaction problems. Our approach involves assessing the performance of heuristic control strategies that are normally hard-coded into scheduling systems, and using probabilistic inference to aggregate this information in light of features of a given problem. BPS, the Bayesian Problem-Solver, introduced a similar approach to solving single-agent and adversarial graph search problems, yielding orders-of-magnitude improvement over traditional techniques. Initial efforts suggest that similar improvements will be realizable when applied to typical constraint-satisfaction scheduling problems.

Hansson, Othar↗

NASA NTRS1993

Decision-theoretic control of EUVE telescope scheduling

This paper describes a decision theoretic scheduler (DTS) designed to employ state-of-the-art probabilistic inference technology to speed the search for efficient solutions to constraint-satisfaction problems. Our approach involves assessing the performance of heuristic control strategies that are normally hard-coded into scheduling systems and using probabilistic inference to aggregate this information in light of the features of a given problem. The Bayesian Problem-Solver (BPS) introduced a similar approach to solving single agent and adversarial graph search patterns yielding orders-of-magnitude improvement over traditional techniques. Initial efforts suggest that similar improvements will be realizable when applied to typical constraint-satisfaction scheduling problems.

Hansson, Othar↗

NASA NTRS1975

Power spectrum analysis of staggered quadriphase-shift-keyed signals

Mathematical analysis of power spectrum of outputs from high-reliability communication system is used to determine system bandwidth. Analysis provides mathematical relationships of signal power spectrum at output of hard limiter for any type of baseband pulse input subjected only to output parameter constraints.

Mcwhorter, F. L.↗

NASA NTRS1980

Cold dense photoionized universes

This investigation employs a computer code, initially constructed for modeling the evolution of a hot dense intergalactic medium (IGM), to study some properties of a cold dense IGM photoionized by QSOs. Within the observational constraints set by flux measurements in the far-ultraviolet, night sky brightness, and hard X-ray region, and the optical depth limits on various QSO spectra, it determines some allowable scenarios for a range of QSO spectral indices (alpha) and cutoff energies. With H(0) = 50 km/s-Mpc, closure density of an IGM (composed of H and He in their cosmic ratio) is possible only if alpha is greater than or equal to 0.1, a circumstance not likely to prevail; the most probable value, alpha = -0.7, implies an upper limit density about 0.35 of closure, which is somewhat larger than previous estimates. These estimates are substantially independent of whether or not QSOs produce the observed diffuse extragalactic X-ray background; such QSO spectral details are critical, however, in determining the ionization of heavy elements that are expected to contaminate a pure primeval plasma.

Sherman, R. D.↗

NASA NTRS1993

Learning Search Control Knowledge for Deep Space Network Scheduling

While the general class of most scheduling problems is NP-hard in worst-case complexity, in practice, for specific distributions of problems and constraints, domain-specific solutions have been shown to perform in much better than exponential time.

Deep Space Network Search Control↗

NASA NTRS2019

Guidance and Navigation Design for a Martian Sample Return Ascent Vehicle

This paper focuses on the work being performed at the NASA Marshall Space Flight Center (MSFC) in support of Mars Ascent Vehicles (MAVs). Specifically, the analysis presented is in support of Martian sample return architectures. In or-der to assess vehicle sensitivities, a detailed simulation tool, (MAV Analysis Tool in Simscape) MANTIS, was implemented using the MATLAB/Simulink Sim-scape architecture. High fidelity navigation sensor models and guidance algorithms were included in order to facilitate sensor requirement development and flight algorithm selection. This work focuses on the performance of the integrated system and the coupling of navigation and guidance capabilities. The architecture trades are heavily dependent on the ascent flight profile chosen. This work assesses both open- and closed-loop guidance algorithms to capture their relative performance and the resulting requirements on sensor capability to support preliminary vehicle design. The analysis builds on previous work that focused on navigation performance for initialization and ascent flight of crewed vehicle. The results provide insight into the coupling between sensor requirements and ascent guidance approach. The analysis provides data to support requirements for hard-ware selection and testing. Additional discussion is also included focusing on other system constraints that affect hardware selection and operational constraints.

Anzalone, Evan↗

NASA NTRS1979

Atmospheric entry systems for advanced Mars missions

A study of estimates of the mass and performance characteristics of entry system designs for advanced Mars missions is presented. The missions were: (1) a Mars Surface Sample Return Mission (MSSR), (2) a Mars Hard Lander, and (3) a Mars Aircraft Mission, and Viking technology or its extensions were used for these entry system conceptual designs. For the MSSR mission, various mission combinations were evaluated including different Mars Ascent Vehicle masses and the use of 2 through 4 stages of the IUS launch vehicle. The constraints for this Mars mission were the Shuttle payload bay geometry limitation and its massive requirements. Requirements for the simple Hard Lander Mission including entry and deceleration, using a parachute and a solid rocket are discussed. A design requirement for the Mars Aircraft Mission to minimize the total entry capsule/aircraft mass by combining entry functions and hardware into the aircraft system was described, and various approaches for supporting the folded aircraft within the aeroshell were examined.

Butts, A. J.↗

NASA NTRS2017

The Atmospheric Response to High Nonthermal Electron Beam Fluxes in Solar Flares. I. Modeling the Brightest NUV Footpoints in the X1 Solar Flare of 2014 March 29

The 2014 March 29 X1 solar flare (SOL20140329T17:48) produced bright continuum emission in the far- and near-ultraviolet (NUV) and highly asymmetric chromospheric emission lines, providing long-sought constraints on the heating mechanisms of the lower atmosphere in solar flares. We analyze the continuum and emission line data from the Interface Region Imaging Spectrograph (IRIS) of the brightest flaring magnetic footpoints in this flare. We compare the NUV spectra of the brightest pixels to new radiative-hydrodynamic predictions calculated with the RADYN code using constraints on a nonthermal electron beam inferred from the collisional thick-target modeling of hard X-ray data from Reuven Ramaty High Energy Solar Spectroscopic Imager. We show that the atmospheric response to a high beam flux density satisfactorily achieves the observed continuum brightness in the NUV. The NUV continuum emission in this flare is consistent with hydrogen (Balmer) recombination radiation that originates from low optical depth in a dense chromospheric condensation and from the stationary beam-heated layers just below the condensation. A model producing two flaring regions (a condensation and stationary layers) in the lower atmosphere is also consistent with the asymmetric Fe II chromospheric emission line profiles observed in the impulsive phase.

Kowalski, Adam F.↗

NASA NTRS2014

High-Energy X-Ray Imaging of the Pulsar Wind Nebula MSH 15-52: Constraints on Particle Acceleration and Transport

We present the first images of the pulsar wind nebula (PWN) MSH 15−52 in the hard X-ray band (8 keV), as measured with the Nuclear Spectroscopic Telescope Array (NuSTAR). Overall, the morphology of the PWN as measured by NuSTAR in the 3-7 keV band is similar to that seen in Chandra high-resolution imaging. However, the spatial extent decreases with energy, which we attribute to synchrotron energy losses as the particles move away from the shock. The hard-band maps show a relative deficit of counts in the northern region toward the RCW 89 thermal remnant, with significant asymmetry. We find that the integrated PWN spectra measured with NuSTAR and Chandra suggest that there is a spectral break at 6 keV, which may be explained by a break in the synchrotron emitting electron distribution at approximately 200 TeV and/or imperfect cross calibration. We also measure spatially resolved spectra, showing that the spectrum of the PWN softens away from the central pulsar B1509−58, and that there exists a roughly sinusoidal variation of spectral hardness in the azimuthal direction. We discuss the results using particle flow models. We find non-monotonic structure in the variation with distance of spectral hardness within 50 of the pulsar moving in the jet direction, which may imply particle and magnetic-field compression by magnetic hoop stress as previously suggested for this source. We also present two-dimensional maps of spectral parameters and find an interesting shell-like structure in the N(sub H) map. We discuss possible origins of the shell-like structure and their implications.

individual objects: G320.4-1.2↗

NASA NTRS1983

Millisecond time variations in hard X-ray solar flares

The results of a search for fast spikes in 2830 hard X-ray solar flares as observed with the hard X-ray burst spectrometer on the Solar Maximum Mission (SMM) are presented. Hundreds of fast spikes with durations of less than 1 sec have been detected at time resolutions of 128 msec and 10 msec. Fast spikes have been detected with rise and decay times as short as 20 msec and with widths as short as 45 msec. They are the fastest hard X-ray variations yet seen from the sun. The observations of such fast variations place new constraints on the physical nature of the source, and these observations and constraints are discussed in terms of nonthermal and thermal models of flares.

Kiplinger, A. L.↗

NASA NTRS1994

The X-ray emission of 3C 273 observed with ASCA

We report preliminary results of an Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of 3C 273. There is no spectral variability within the ASCA observation, in contrast to the longer term behavior found with European X-ray Observatory Satellite (EXOSAT) and Ginga which established significant changes in the spectral index of the power-law continuum on timescales of a week or more, uncorrelated with luminosity. Comparison of the ASCA data with a simultaneous Roentgen Satellite (ROSAT) Ginga observation in 1990 December shows that while the shape of the spectrum above approximately 1 keV is essentially the same, the flux in the soft component, below approximately 1 keV, considerably weaker relative to the hard component in the ASCA observation. The 2-10 keV luminosity is at least a factor of approximately 1.5 greater in the ASCA observation than in the ROSAT/Ginga observation while the ratio of 2-10 keV luminosity to 0.4-1.0 keV luminosity increases by a factor of approximately 1.2. Thus the spectral shape of the hard component appears to be independent of the relative magnitude of the soft component and is an important constraint on emission and reprocessing models. We find no significant Fe K line-emission in this observation. The data also highlight very well some of the outstanding problems in the instrumental responses.

Yaqoob, Tahir↗

NASA NTRS1976

Design criteria for noncoherent Gaussian channels with MFSK signaling and coding

This paper presents data and criteria to assess and guide the design of modems for coded noncoherent communication systems subject to practical system constraints of power, bandwidth, noise spectral density, coherence time, and number of orthogonal signals M. Three basic receiver types are analyzed for the noncoherent multifrequency-shift keying (MFSK) additive white Gaussian noise channel: hard decision, unquantized (optimum), and quantized (soft decision). Channel capacity and computational cutoff rate are computed for each type and presented as functions of the predetection signal-to-noise ratio and the number of orthogonal signals. This relates the channel constraints of power, bandwidth, coherence time, and noise power to the optimum choice of signal duration and signal number.

Butman, S. A.↗

NASA NTRS1992

Nonthermal electron-positron pairs and the break in the hard X-ray spectrum of NGC 4151

The recent observation by the detectors on board Granat of a spectral steepening above about 50 keV imposes a constraint on possible emission models for NGC 4151. This steepening, for example, is not well fitted by an exponential rollover characteristic of a purely thermal model, or by a Compton-downscattered power law. We find that this spectral behavior is consistent with that produced by a photon-starved nonthermal pair plasma with high compactness. This is the first quantitative test of the nonthermal pair plasma model against broad-band X-ray/gamma-ray observations. Above 200 keV or so, the nonthermal pair plasma model predicts an upturn in the spectrum, and a thermal annihilation feature around 511 keV. Such spectral behavior should be looked for with GRO.

Coppi, Paolo S.↗