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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 55 records · Page 3
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NASA NTRS1992

X-ray variability of Scorpius X-1 during a multiwavelength campaign

Consideration is given to the X-ray variability of Scorpius X-1, which was observed with Ginga on March 9-11, 1989 as part of a multiwavelength campaign. The temporal characteristics observed, including quasi-periodic oscillations, HF noise, and VLF noise, are consistent with previous observations of Sco X-1. Quasi-periodic oscillations are observed on both the normal branch and the lower flaring branch, but not on the upper flaring branch. Limits are placed on the fractional rms variation of quasi-period oscillations on the upper flaring branch of less than or approximately equal to 2 percent of the total intensity. The characteristics of the observed red noise components are found to vary along the flaring branch. The fractional rms variation of VLF noise increases from less than 2 to greater than 6 percent as Sco X-1 moves from the flaring branch-normal branch vertex to the upper end of the flaring branch.

Hertz, P.↗
NASA NTRS1993

Multiwavelength Pyrometry To Correct For Reflections

Computerized curve fitting yields more and better information on thermal radiation. Multiwavelength pyrometry involves measurement of spectrum of thermal radiation emitted by and reflected from specimen. Auxiliary source enables determination of spectral reflectance of specimen. Spectral reflectance and temperature of specimen obtained from spectral measurements by nonlinear least-squares curve-fitting routine.

Ng, Daniel↗
NASA NTRS1992

The high-energy transient experiment (HETE) - An international multiwavelength mission

The High Energy Transient Experiment (HETE), an international mission scheduled by NASA for launch on a Pegasus rocket in July 1994, is described. The prime objective of HETE is to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft. A unique feature of the HETE mission is its capability to localize GRBs with about 10 arc second accuracy, in near real time aboard the spacecraft, and to transmit these positions directly to a network of receivers at existing ground-based observatories, enabling rapid, sensitive follow-up studies in the radio, IR, and optical bands.

Ricker, George R.↗
NASA NTRS1993

Multi Wave Link: An interactive database for co-ordination of multiwavelength programs

Multi Wave Link is an operational database used by the international astronomical community to plan and coordinate multiwavelength observational campaigns on various celestial objects. This facility has been and continues to be an essential tool for the organization of numerous simultaneous ground-based and satellite observations. The Multi Wave Link system has both an interactive component and an electronic mail alert notice component. The interactive portion contains a database of schedules from several of the world's larger observatories and orbiting satellites. Lists of observers, observatories, and their available instrumentation are additionally contained in the system. Another feature added to the software allows the user to search the Royal Greenwich Observatory e-mail listing of international astronomers. This capability is often used by astronomers to find the electronic address of colleagues for improved communication. However, the most productive aspect of the Multi Wave Link system appears to be one of the simplest parts of the system: the electronic mail alert notices for observing campaigns. Information useful in planning the structure of future astronomical databases can be obtained by studying patterns of use of the Multi Wave Link system. This paper analyzes 22 months of Multi Wave Link usage from Sep. 1991 - Jul. 1993.

Cordova, France↗
NASA NTRS1992

Full-spectrum multiwavelength pyrometry for nongray surfaces

A full-spectrum (encompassing radiation on both sides of the Wien displacement peak) multiwavelength pyrometer was developed. It measures the surface temperature of arbitrary nongray ceramics by curve fitting a spectrum in this spectral region to a Planck function of temperature T. This function of T is modified by the surface spectral emissivity. The emissivity function was derived experimentally from additional spectra that were obtained by using an auxiliary radiation source and from application of Kirchhoff's law. This emissivity was verified by results that were obtained independently by using electromagnetic and solid-state theories. In the presence of interfering reflected radiation this general pyrometry improves the accuracy of the measured temperature by measuring an additional spectrum that characterizes the interfering radiation source.

Ng, Daniel↗
NASA NTRS1994

Multiwavelength observations of Hercules X-1/HZ Herculis

We present first results from a multiwavelength campaign to observe the binary pulsar system Her X-1/ HZ Her. The campaign spanned 4 days during 1993 August: observations were taken with five satellites (IUE, EUVE, ROSAT, ASCA, and CGRO/BATSE) and several ground-based facilities. A substantial, unexpected drop in flux at X-ray energies, with no change in absorbing column density, was observed. The pulse period has increased from the previous measurement, contrary to the usual spin-up, and no pulsed emission is detected above 0.9 keV in the low state. The optical and UV fluxes continued to show 1.7 day modulation attributed to X-ray heating of the companion star. However, the significant reduction in UV flux observed around eclipse implies an absence of the normally observed excess attributed to X-ray heating of the disk. We conclude that we have observed an anomalous low state, seen only once before (Parmar et al. 1985), in which the X-ray flux is not redistributed but obscured. We suggest explanations for the behavior of the flux at different wavelengths.

Vrtilek, S. D.↗
NASA NTRS1994

The 1993 multiwavelength campaign on 3C 279: The radio to gamma-ray energy distribution inlow state

Simultaneous observations of 3C 279 at radio, millimeter, near-infrared, optical, ultraviolet (with IUE) and X-ray (with ROSAT) wavelengths were obtained in 1992 December-1993 January, during a three week pointing at the source by the Compton Gamma Ray Observatory. The blazar was in a quiescent or 'low' state during this period. Comparing the multiwavelength energy distribution to that from 1991 June, when 3C 279 was in its brightest recorded gamma-ray state, we find the following: (1) 3C 279 faded dramatically at all frequencies above 10(exp 14) Hz, while the flux variations at low frequencies (radio to millimeter wavelengths) were minor. (2) The near-infrared-optical-ultraviolet spectral shape was softer (steeper) in the quiescent state, and the X-ray spectra also appear softer, although the spectral indix measured by ROSAT refer to a lower energy band than that measured earlier with Ginga. (3) The ratio of the gamma-ray luminosity to that across all other frequencies decreased from a value of approximately equal to 10 in the flaring state to a value approximately equal to 1 in the quiescent state. These findings imply that the production of gamma-rays is closely related to the optical-ultraviolet continuum, in agreement with models where gamma-rays are produced through inverse Compton (IC) scattering by relativistic electrons emitting the synchrotron continuum. The observed nonlinear relation between the synchrotron and IC requires both a change in the electron spectrum and an associated change in the seed photons.

Maraschi, L.↗
NASA NTRS1994

The international AGN watch: A multiwavelength monitoring consortium

The International AGN Watch, an informal consortium of over 100 astronomers, was established to coordinate multiwavelength monitoring of a limited number of active galactic nuclei and thus obtain comprehensive continuum and emission-line variability data with unprecedented temporal and wavelength coverage. We summarize the principal scientific results from two completed space-based and ground-based campaigns on the Seyfert galaxies NGC 5548 and NGC 3783. We describe a project in progress and outline our future plans.

Alloin, D.↗
NASA NTRS1995

Multiwavelength Observations of Markarian 421 During a TeV/X-Ray Flare

A TeV flare from the BL Lac object Mrk 421 was detected in May of 1994 by the Whipple Observatory air Cherenkov experiment during which the flux above 250 GeV increased by nearly an order of magnitude over a 2-day period. Contemporaneous observations by ASCA showed the X-ray flux to be in a very high state. We present these results, combined with the first ever simultaneous or nearly simultaneous observations at GeV gamma-ray, UV, IR, mm, and radio energies for this nearest BL Lac object. While the GeV gamma-ray flux increased slightly, there is little evidence for variability comparable to that seen at TeV and X-ray energies. Other wavelengths show even less variability. This provides important constraints on the emission mechanisms at work. We present the multiwavelength spectrum of this gamma-ray blazar for both quiescent and flaring states and discuss the data in terms of current models of blazar emission.

Bertsch, D. L.↗
NASA NTRS1997

Temperature Measurement of a Glass Material Using a Multiwavelength Pyrometer

Temperature measurement of a substance that is transparent using the traditional 1-color, 2-color and other pyrometers has been difficult. The radiation detected by pyrometers do not come from a well defined location in the transparent body. The multiwavelength pyrometer developed at the NASA Lewis Research Center can measure the surface temperature of many materials. We show in this paper that it also measures the surface and a bulk subsurface temperature of transparent materials like glass.

Ng, Daniel↗
NASA NTRS1997

Multiwavelength and Statistical Research in Space Astrophysics

The accomplishments in the following three research areas are summarized: multiwavelength study of active galactic nuclei; magnetic activity of young stellar objects; and statistical methodology for astronomical data analysis. The research is largely based on observations of the ROSAT and ASCA X-ray observatories, complemented by ground-based optical and radio studies. Major findings include: discovery of inverse Compton X-ray emission from radio galaxy lobes; creation of the largest and least biased available sample of BL Lac objects; characterization of X-ray and nonthermal radio emission from T Tauri stars; obtaining an improved census of young stars in a star forming region and modeling the star formation history and kinematics; discovery of X-ray emission from protostars; development of linear regression methods and codes for interpreting astronomical data; and organization of the first cross-disciplinary conferences for astronomers and statisticians.

Feigelson, Eric D.↗
NASA NTRS1997

A Multiwavelength Study of the Starburst Galaxy NGC 7771

We present a multiwavelength study of the interacting starburst galaxy NGC 7771, including new optical and ultra-violet spectra and a previously unpublished soft X-ray ROSAT image and spectrum. The far-infrared, radio, and X-ray fluxes suggest that a massive burst of star-formation is currently in progress but the small equivalent width of the Balmer emission lines (equivalent width H(alpha approximately equals 100 A), the weak UV flux, the low abundance of ionised oxygen, and the shape of the optical spectrum lead us to conclude that there are few 0 stars. This might normally suggest that star-formation has ceased but the galaxy's barred gravitational potential and large gas reserves imply that this should not be so, and we therefore consider other explanations. We argue that the observations cannot be due to effects of geometry, density bounded nebulae, or dust within the nebulae, and conclude that a truncated IMF is required. The dwarf galaxy NGC 7770 appears to be in the initial stages of a merger with NGC 7771, and the resulting tidal perturbations may have induced the apparent two-armed spiral pattern, and driven a substantial fraction of the disk gas inwards. The presence of a bulge in NGC 7771 may be moderating the starburst so that, while still occuring on a large scale with a supernova rate of 0.8-1/yr, it is less violent and the IMF has a relatively low upper mass limit. We find that there is a cluster of stars obscuring part of the starburst region, and we offer an explanation of its origin.

Davies, Richard I.↗
NASA NTRS1997

Multiwavelength Blazar Studies

The present report concerns the following projects 'High energy emission from hot accretion disks from active galactic nuclei'; 'OSSE spectral timing and monitoring observations of Cygnus X- 1'; 'OSSE observations of blazars'; and 'Search for correlated time variations of bright EGRET blazars'. The most favored model for the central engine inAGNs is the supermassive black hole hypothesis (Rees 1978). The observed luminosities range from approx. 10 logical and 44-45 erg /s for objects such as Mk 421 and Seyferts to as much as approx. 10logical and 47 for powerful QSOs such as 3C 273 and 3C 279, a large fraction of the observed bolometric luminosity being, in all likelihood, beamed. As such, these objects are strong X-ray emitters (cf. Makino et al. 1987) and often undergo gamma-ray flaring detected at the EGRET range (Hartman et al. 1992) and in the case of one of two known nearby BL Lacs, Mk 421, at TeV energies as well (Punch et al. 1992, Macomb et al. 1995). Previous campaigns emphasizing radio through X-ray and even gamma-ray observations have generally found that the multiwavelength spectrum is adequately fit by a standard synchrotron self-Compton (SSC-cf. Jones et al. 1974) model of a relativistic jet (e.g. Makino et al. 1987 and Macomb et al. 1995 for the BL Lac object Mk 421) or inhomogeneous relativistic jet (Mufson et al 1990). It also was examined the gamma-gamma transperency constraints inblazars.

Kafatos, Menas↗
NASA NTRS1997

Multiwavelength Blazar Studies

The discovery of a multitude of strongly gamma-ray emitting AGNs by EGRET and the detection of at least two AGNs at even higher energies by the Whipple Collaboration generated much interest in the study of those objects and extensive observations were conducted in the following years. The Michigan group concentrated its effort on continued observations of the two TeV gamma-ray sources, Markarian 421 and Markarian 501, to monitor variability in the high energy emission as well as to provide simultaneous measurements during multiwavelength observations of these objects.

Source record↗
NASA NTRS1998

Remote Heat Flux Using a Self Calibration Multiwavelength Pyrometer and a Transparent Material

A self calibrating multiwavelength pyrometer was used to conduct remote heat flux measurements using a transparent sapphire disk by determining the sapphire disk's front and back surface temperatures. Front surface temperature (Tfs) was obtained from detection of surface emitted radiation at long wavelengths (k = 6 gm). Back surface temperature (Tbs) was obtained from short wavelength (1 to 5 gm) radiation transmitted through the sapphire disk. The thermal conductivity of the sapphire disk and the heat transfer coefficients h, and h2 of its surfaces are determined experimentally. An analysis of the heat flux measurement is presented.

Ng, Daniel↗
NASA NTRS1998

Remote Heat Flux Measurement Using a Self Calibration Multiwavelength Pyrometer and a Transparent Material

A self calibrating multiwavelength pyrometer was used to conduct remote heat flux measurements using a transparent sapphire disk by determining the sapphire disk's front and back surface temperatures. Front surface temperature (Tfs) was obtained from detection of surface emitted radiation at long wavelengths (lambda > 6 micrometers). Back surface temperature (Tbs) was obtained from short wavelength (1 to 5 micrometers) radiation transmitted through the sapphire disk. The thermal conductivity k of the sapphire disk and the heat transfer coefficients h(sub 1) and h(sub 2) of its surfaces are determined experimentally. An analysis of the heat flux measurement is presented.

Ng, Daniel↗
NASA NTRS1999

Temperature Measurement of a Miniature Ceramic Heater in the Presence of an Extended Interfering Background Radiation Source Using a Multiwavelength Pyrometer

Temperature measurement of small (millimeter size) objects is generally difficult and demanding. Measurement involving ceramic materials using the traditional one- and two-color pyrometer is difficult because of their complex optical properties, such as low emissivity which may vary with both temperature and wavelength. Pyrometry applications in an environment with an interfering radiation source of extended dimension adds extra complexity to the process. We show that the multiwavelength pyrometer successfully measured the temperatures of a millimeter (mm) size ceramic heater under these demanding conditions.

Ng, Daniel↗
NASA NTRS1999

Multiwavelength Observations of Mkn 501 During the 1997 High State

During the observation period 1977, the close Blazar Mkn 501 showed extremely strong emission and high variability. We examine multiwavelength aspects of this event using Radio optical, soft and hard X-ray and TeV data. We concentrate on the medium-timescale variability of the broadband spectra averaged over 1-week intervals. We confirm the previously found correlation between soft and hard X-ray emission and the at TeV energies while the source shows only minor variability at radio and optical wavelengths. The non-linear correlation between hard X-ray and TeV fluxes is consistent with a simple analytic estimate based on an SSC model in which Klein-Nishina effects are important for the highest-energy electrons in the jet and flux; variations are caused by variations of the electron density and/or the spectral index of the electron injection spectrum. The time-averaged spectra are fitted with an SSC dominated leptonic jet model using the full Klein-Nishina cross section and following the self-consistent evolution of relativistic particles along the jet accounting for gamma gamma absorption and pair production within the source as well as due to the intergalactic infrared red background radiation. The contribution from external inverse-Compton scattering is tightly constrained by the low maximum EGRET flux and found co be negligible.

Petry, D.↗