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NASA NTRS2012

Toward a Unified AGN Structure

We present a unified model for the structure and appearance of accretion powered sources across their entire luminosity range from galactic X-ray binaries (XRB) to luminous quasars, with emphasis on AG N and their phenomenology. Central to this model is the notion of MHD winds launched by the accretion disks that power these objects. These winds provide the matter that manifests as blueshifted absorption features in the UV and X-ray spectra of a large fraction of these sources; furthermore, their density distribution in the poloidal plane determines their "appearance" (i.e. the column and velocity structure of these absorption features and the obscuration of the continuum source) as a function of the observer inclination angle (a feature to which INTEGRAL has made significant contributions). This work focuses on just the broadest characteristics of these objects; nonetheless, it provides scaling laws that allow one to reproduce within this model the properties of objects extending in luminosity from luminous quasars to XRBs. Our general conclusion is that the AGN phenomenology can be accounted for in terms of three parameters: The wind maSS flux in units of the Eddington value, m(dot), the observers' inclination angle Theta and the logarithmic slope between the 0/UV and X-ray fluxes alpha(sub ox); however because of a correlation between alpha(sub ox) and UV luminosity the number of significant parameters is two. The AGN correlations implied by this model appear to extend to and consistent with the XRB phenomenology, suggesting the presence of a truly unified underlying structure for accretion powered sources.

Kazanas, Demosthenes↗
NASA NTRS2018

A NICER Spectrum of MAXI J1535-571: Near-Maximal Black Hole Spin and Potential Disk Warping

We report on a Neutron star Interior Composition Explorer (NICER) observation of the Galactic X-ray binary and stellar-mass black hole candidate, MAXI J1535−571. The source was likely observed in an "intermediate" or "very high" state, with important contributions from both an accretion disk and hard X-ray corona. The 2.3-10 keV spectrum shows clear hallmarks of relativistic disk reflection. Fits with a suitable model strongly indicate a nearmaximal spin parameter of a = cJ/GM(exp 2) = 0.994(2) and a disk that extends close to the innermost stable circular orbit, r/r(sub ISCO) = 1.08(8) (1σ statistical errors). In addition to the relativistic spectrum from the innermost disk, a relatively narrow Fe K emission line is also required. The resolution of NICER reveals that the narrow line may be asymmetric, indicating a specific range of emission radii. Fits with a relativistic line model suggest an inner radius of r = 144 +140/-60 GM/c(exp 2) for the putative second reflection geometry; full reflection models suggest that radii a few times larger are possible. The origin of the narrow line is uncertain, but a warp likely provides the most physically plausible explanation. We discuss our results in terms of the potential for NICER to reveal new features of the inner and intermediate accretion disk around black holes.

Miller, J. M.↗
NASA NTRS2018

The Zwicky Transient Facility: Data Processing, Products, and Archive

The Zwicky Transient Facility (ZTF) is a new robotic time-domain survey currently in progress using the Palomar 48-inch Schmidt Telescope. ZTF uses a 47 square degree field with a 600 megapixel camera to scan the entire northern visible sky at rates of ∼3760 square degrees/hour to median depths of g ~ 20.8 and r ~ 20.6 mag (AB, 5σ in 30 sec). We describe the Science Data System that is housed at IPAC, Caltech. This comprises the data-processing pipelines, alert production system, data archive, and user interfaces for accessing and analyzing the products. The real-time pipeline employs a novel image-differencing algorithm, optimized for the detection of point-source transient events. These events are vetted for reliability using a machine-learned classifier and combined with contextual information to generate data-rich alert packets. The packets become available for distribution typically within 13 minutes (95th percentile) of observation. Detected events are also linked to generate candidate moving-object tracks using a novel algorithm. Objects that move fast enough to streak in the individual exposures are also extracted and vetted. We present some preliminary results of the calibration performance delivered by the real-time pipeline. The reconstructed astrometric accuracy per science image with respect to Gaia DR1 is typically 45 to 85 milliarcsec. This is the RMS per-axis on the sky for sources extracted with photometric S/N ≥10 and hence corresponds to the typical astrometric uncertainty down to this limit. The derived photometric precision (repeatability) at bright unsaturated fluxes varies between 8 and 25 millimag. The high end of these ranges corresponds to an airmass approaching ∼2—the limit of the public survey. Photometric calibration accuracy with respect to Pan-STARRS1 is generally better than 2%. The products support a broad range of scientific applications: fast and young supernovae; rare flux transients; variable stars; eclipsing binaries; variability from active galactic nuclei; counterparts to gravitational wave sources; a more complete census of Type Ia supernovae; and solar-system objects.

Frank J. Masci↗
NASA NTRS2022

Fermi Gamma-ray Space Telescope

The Fermi Gamma-ray Space Telescope, a key mission in multiwavelength and multimessenger studies, has been surveying the γ-ray sky from its low-Earth orbit since 2008. Its two scientific instruments, the Gamma-ray Burst Monitor (GBM) and the Large Area Telescope (LAT), cover 8 orders of magnitude in photon energy. The GBM consists of 12 Sodium Iodide detectors and 2 Bismuth Germinate detectors, covering the 10 keV - 40 MeV energy range, arrayed on two sides of the spacecraft so as to view the entire sky that is not occulted by the Earth. The LAT is a pair production telescope based on silicon strip trackers, a Cesium Iodide calorimeter, and a plastic scintillator anticoincidence system. It covers the energy range from about 20 MeV to more than 500 GeV, with a field of view of about 2.4 steradians. Thanks to their huge fields of view, the instruments can observe the entire sky with a cadence of about an hour for GBM and about three hours for LAT. All γ-ray data from Fermi become public immediately, enabling a broad range of multiwavelength and multimessenger research. Over 3000 γ-ray bursts (GRBs), including GRB 170817A associated with a neutron star merger detected in gravitational waves, and 5000 high-energy sources, including the blazar TXS 0506+056 associated with high-energy neutrinos, have been detected by the Fermi instruments. The Fermi Science Support Center provides a wide array of resources to enable scientific use of the data, including background models, source catalogs, analysis software, documentation, and a Help Desk.

gamma rays↗
NASA NTRSDate not supplied

High EneRgy Observatory for Imaging X-rays (HEROIX) Mission Concept

The High EneRgy Observatory for Imaging X-rays (HEROIX) is a next-generation broadband X-ray space telescope concept under development as a Medium-Class Explorer mission. Building on more than three decades of replicated NiCo shell technology at NASA’s Marshall Space Flight Center, HEROIX will deliver 5 arcsecond half-power-diameter imaging resolution in the hard X-ray band. The observatory will incorporate four co-aligned telescopes with advanced multilayer coatings, extending the bandpass into the hard X-ray regime and providing an integrated effective area of 380 cm² at 30 keV. A suite of focal plane detectors will enable imaging capability throughout its 1–80 keV bandpass. This combination of angular resolution and high-energy coverage will open new windows into non-thermal processes in extreme astrophysical environments. HEROIXwill deliver transformative science, advancing the astrophysics community’s understanding of supernova physics, the X-ray binary population of the Galactic Center, accretion-driven galaxy evolution, and the origin of the Cosmic X-ray Background.

Nick Thomas↗
NASA NTRS2007

Hubble 2006: Science Year in Review

The 10 science articles selected for this years annual science report exemplify the range of Hubble research from the Solar System, across our Milky Way, and on to distant galaxies. The objects of study include a new feature on Jupiter, binaries in the Kuiper Belt, Cepheid variable stars, the Orion Nebula, distant transiting planets, lensing galaxies, active galactic nuclei, red-and-dead galaxies, and galactic outflows and jets. Each narrative strives to construct the readers understanding of the topics and issues, and to place the latest research in historical, as well as scientific, context. These essays reveal trends in the practice of astronomy. More powerful computers are permitting astronomers to study ever larger data sets, enabling the discovery of subtle effects and rare objects. (Two investigations created mosaic images that are among the largest produced to date.) Multiwavelength data sets from ground-based telescopes, as well as other great observatories Spitzer and Chandraare increasingly important for holistic interpretations of Hubble results. This yearbook also presents profiles of 12 individuals who work with Hubble, or Hubble data, on a daily basis. They are representative of the many students, scientists, engineers, and other professions who are proudly associated with Hubble. Their stories collectively communicate the excitement and reward of careers related to space science and technology.

Hubble space telescope↗
NASA NTRS1992

Detection and period measurements of GX1+4 at hard x ray energies with the SIGMA telescope

The galactic Low Mass X ray Binary GX1+4 was detected by the coded aperture hard X ray gamma ray SIGMA telescope during the Feb. to April 1991 observations of the galactic center regions. The source, whose emission varied during the survey of a factor greater than 40 pct., reached a maximum luminosity in the 40 to 140 energy range of 1.03 x 10(exp 37) erg/s (D = 8.5 kpc), thus approaching the emission level of the 1970 to 1980 high state. Two minute flux pulsations were detected on Mar. 22 and on Mar. 31 and Apr. 1. Comparison with the last period measurements shows that the current spin-down phase of GX1+4 is ending. Concerning the proposed association of this source with the galactic center 511 keV annihilation emission, upper limits were derived.

Laurent, PH.↗
NASA NTRS2018

The NANOGrav 11 Year Data Set: Pulsar-Timing Constraints on the Stochastic Gravitational-Wave Background

We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released 11 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no evidence for a GWB, we place constraints on a population of inspiraling supermassive black hole (SMBH) binaries, a network of decaying cosmic strings, and a primordial GWB. For the first time, we find that the GWB constraints are sensitive to the solar system ephemeris (SSE) model used and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first pulsar-timing array (PTA) constraints that are robust against SSE errors. We thus place a 95% upper limit on the GW-strain amplitude of A (sub GWB) < 1.45 × 10 (exp -15) at a frequency of f=1 yr(exp -1) for a fiducial f (exp -2/3) power-law spectrum and with interpulsar correlations modeled. This is a factor of approximately 2 improvement over the NANOGrav nine-year limit calculated using the same procedure. Previous PTA upper limits on the GWB (as well as their astrophysical and cosmological interpretations) will need revision in light of SSE systematic errors. We use our constraints to characterize the combined influence on the GWB of the stellar mass density in galactic cores, the eccentricity of SMBH binaries, and SMBH-galactic-bulge scaling relationships. We constrain the cosmic-string tension using recent simulations, yielding an SSE-marginalized 95% upper limit of G (sub mu) < 5.3 × 10(exp -11) - a factor of approximately 2 better than the published NANOGrav nine-year constraints. Our SSE-marginalized 95% upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation universe) is omega (sub GWB)(f) h (exp 2) < 3.4 × 10 (exp -10).

Supermassive Black Holes↗
NASA NTRS1972

Binary stars as X-ray sources.

The idea that many if not most of the powerful galactic X-ray sources are generated in binary star systems containing at least one exotic object with gas is examined. Past studies lending support to this hypothesis are reviewed, and major features of galactic X-ray sources that require explanations are delineated. Attention is given to conclusions gained from optical studies of close binaries and to promising areas of further investigation stemming from the concept of binary stars as X-ray sources.

Burbidge, G.↗
NASA NTRS1991

A post-core-collapse model for the nucleus of M33

A model for the post-collapse core of M33 is proposed. By analogy with globular clusters, the formation of tight binary systems powers the reexpansion of the core, and it is expected that low-mass X-ray binaries form at a rate about equal to that of all galactic globular clusters combined. About a dozen such binaries should be present, and their combined emission may explain the large and enigmatic unresolved X-ray emission from the nucleus of M33. In addition, tidal formation of cataclysmic binaries may lead to a nova rate of more than about one per century. Numerous blue stragglers have probably formed through mergers caused by stellar collisions, but their density is probably too low to explain the blue color of the nucleus. Young stars are the likely cause for the color, and their presence may complicate the simple dynamical picture presented here.

Hernquist, Lars↗
NASA NTRS1982

X-ray illumination of globular cluster puzzles

Globular clusters are thought to be among the oldest objects in the Galaxy, and provide, in this connection, important clues for determining the age and process of formation of the Galaxy. The present investigation is concerned with puzzles relating to the X-ray emission of globular clusters, taking into account questions regarding the location of X-ray emitting clusters (XEGC) unusually near the galactic plane and/or galactic center. An adopted model is discussed for the nature, formation, and lifetime of X-ray sources in globular clusters. An analysis of the available data is conducted in connection with a search for correlations between binary formation time scales, central relaxation times, galactic locations, and X-ray emission. The positive correlation found between distance from galactic center and two-body binary formation time for globular clusters, explanations for this correlation, and the hypothesis that X-ray sources in globular clusters require binary star systems provide a possible explanation of the considered puzzles.

Lightman, A. P.↗
NASA NTRS2017

An XMM-Newton and NuSTAR Study of IGR J18214-1318: A Non-Pulsating High-Mass X-Ray Binary with a Neutron Star

IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to determine the nature of the compact object in this system. This source exhibits high levels of aperiodic variability, but no periodic pulsations are detected with a 90% confidence upper limit of 2% fractional rms between 0.00003-88 Hz, a frequency range that includes the typical pulse periods of neutron stars (NSs) in HMXBs (0.1-103 s). Although the lack of pulsations prevents us from definitively identifying the compact object in IGR J18214-1318, the presence of an exponential cutoff with e-folding energy < 30 keV in its 0.3-79 keV spectrum strongly suggests that the compact object is an NS. The X-ray spectrum also shows a Fe Kα emission line and a soft excess, which can be accounted for by either a partial-covering absorber with NH approximately equals 10(exp23)cm(exp−2), which could be due to the inhomogeneous supergiant wind, or a blackbody component with = - kT 1.74+0.05 0.04 keV and R >> 0.3 BB km, which may originate from NS hot spots. Although neither explanation for the soft excess can be excluded, the former is more consistent with the properties observed in other supergiant HMXBs. We compare IGR J18214-1318 to other HMXBs that lack pulsations or have long pulsation periods beyond the range covered by our observations.

Fornasini, Francesca M.↗
NASA NTRS2013

Energy Feedback from X-ray Binaries in the Early Universe

X-ray photons, because of their long mean-free paths, can easily escape the galactic environments where they are produced, and interact at long distances with the intergalactic medium, potentially having a significant contribution to the heating and reionization of the early universe. The two most important sources of X-ray photons in the universe are active galactic nuclei (AGNs) and X-ray binaries (XRBs). In this Letter we use results from detailed, large scale population synthesis simulations to study the energy feedback of XRBs, from the first galaxies (z (redshift) approximately equal to 20) until today.We estimate that X-ray emission from XRBs dominates over AGN at z (redshift) greater than or approximately equal to 6-8. The shape of the spectral energy distribution of the emission from XRBs shows little change with redshift, in contrast to its normalization which evolves by approximately 4 orders of magnitude, primarily due to the evolution of the cosmic star-formation rate. However, the metallicity and the mean stellar age of a given XRB population affect significantly its X-ray output. Specifically, the X-ray luminosity from high-mass XRBs per unit of star-formation rate varies an order of magnitude going from solar metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs per unit of stellar mass peaks at an age of approximately 300 Myr (million years) and then decreases gradually at later times, showing little variation for mean stellar ages 3 Gyr (Giga years, or billion years). Finally, we provide analytical and tabulated prescriptions for the energy output of XRBs, that can be directly incorporated in cosmological simulations.

galaxies↗
NASA NTRS2016

Exploring X-Ray Binary Populations in Compact Group Galaxies With Chandra

We obtain total galaxy X-ray luminosities, LX, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the +/-1σ scatter of the Mineo et al. LX-star formation rate (SFR) correlation or have higher LX than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. LX-stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme LX values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high LX values can be observed due to strong XRB variability.

X-rays: binaries↗
NASA NTRS1976

Binary X-ray stars and supernovae of type I

Most of the strong galactic X-ray sources must be low-mass close binary systems, such as Her X-1 and Sco X-1. Two evolutionary scenarios are discussed, both involving type I supernovae that occur when mass-accreting white dwarfs are driven over their mass limit. In one, accepting the correctness of the idea that a neutron star or black hole is the seat of the X-ray emission, the SN occurs before the system is an X-ray source. Another possibility is that the white dwarf is the X-ray source, just prior to its collapse and the ensuing SN.

Gursky, H.↗
NASA NTRS2003

Chandra Observations of the Faintest Low-Mass X-ray Binaries

There exists a group of persistently faint galactic X-ray sources that, based on their location in the galaxy, high L(sub X)/L(sub opt), association with X-ray bursts, and absence of low frequency X-ray pulsations, are thought to be low-mass X-ray binaries (LMXBs). We present results from Chandra observations for 8 of these systems: 4U 1708-408, 2S 1711-339, KS 1739-304, SLX 1735-269, GRS 1736-297, SLX 1746-331, 1E 1746.7-3224, and 4U 1812-12. Locations for all sources, excluding GRS 1736-297, SLX 1746-331, and KS 1739-304 (which were not detected) were improved to 0.6 sec error circles (90% confidence). Our observations support earlier findings of transient behavior of GRS 1736-297, KS 1739-304, SLX 1746-331, and 2S 1711-339 (which we detect in one of two observations). Energy spectra for 4U 1708-408,2S 1711-339, SLX 1735-269, 1E 1746.7-3224, and 4U 1812-12 are hard, with power law indices typically 1.4-2.1, which are consistent with typical faint LMXB spectra.

Wilson, Colleen A.↗
NASA NTRS2008

LISA: Astrophysics Out to z Approximately 10 with Low-Frequency Gravitational Waves

This viewgraph presentation reviews the Laser Interferometer Space Antenna (LISA). LISA os a joint ESA-NASA project to design, build and operate a space-based gravitational wave detector. The 5 million Kilometer long detector will consist of three spacecraft orbiting the Sun in a triangular formation. Space-Time strains induced by gravitational waves are detected by measuring changes in the separation of fiducial masses with laser interferometry. LISA is expected to detect signals from merging massive black holes, compact stellar objects spiraling into super massive black holes in galactic nuclei, thousands of close binaries of compact objects in the Milky way and possible backgrounds of cosmological origin.

Stebbins, Robin T.↗
NASA NTRS1975

Interim Report of the Astronomy Spacelab Payloads Study: Ultraviolet and Optical Astronomy - Volume 2

The Space Shuttle will comprise NASA's primary transportation system into near-earth orbit during the 1980s. The Shuttle will provide the astronomical community with a major new capability to send a wide variety of instrumentation into orbit, to utilize it there under manned or automatic control for periods from seven to thirty days, and to return it to the ground. To this end the European Space Research Organization (ESRO) is developing Spacelab, an array of interchangeable components -pressurized manned modules, unpressurized pallets and related support systems - to be mounted in the Shuttle payload bay. Spacelab will offer important opportunities to carry out astronomical research with instruments optimized for specific objectives. With a high flight frequency and with the ability to modify or interchange telescopes and instruments between flights, one will not need to make rigid long-term commitments to specific and compromised telescope/instrument/ detector combinations as is the case for automated satellites. Observational techniques demanding the physical return of data and equipment - in particular the use of photographic film, instruments requiring tight calibration controls, cryogens, high-risk detectors and degradeable optical coatings -will open research areas not readily addressed by automated satellites. Although Shuttle flight duration will be limited to periods from seven to thirty days, substantial data can be obtained with a single instrument on short missions, if targets are carefully selected and prioritized, and a large number of instruments can be accommodated on a single flight. Important astronomical data are regularly obtained on sounding rocket flights of five minutes duration. Spacelab will provide far longer observing periods for large and small telescopes, with resources greatly exceeding those of sounding rockets, while retaining much of the sounding rocket philosophy in terms of instrument flexibility, simplicity, reliability assurance and development costs. The Ultraviolet and Optical Astronomy Program on Spacelab is being planned to provide optical astronomers with relatively simple and regular access to the extended wavelength coverage, the superior image quality and the darkness of the night sky available above the earth's atmosphere. In a rapidly evolving science one cannot predict what problems will be timely in the 1980s. Extrapolating from the current epoch, however, one can envision a continuing interest in such areas as the structure, composition and phenomenology of planetary surfaces and atmospheres; the composition and physical nature of the interstellar medium; the composition, structure and life history of stars, especially those in advanced stages of evolution; the stellar population of other galaxies; such enigmatic phenomena as X-ray binary black holes, pulsars, active galactic nuclei and quasars; large scale interactions between galaxies and the nature of the intergalactic medium; precise calibration of the Hubble law for the expansion of the universe; the average density of the universe; and the existence of extraterrestrial life.

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