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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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NASA NTRS1979

Soft X-ray emission from the Lupus Loop and Sn 1006 supernova remnants

X-ray maps of the Lupus region have been obtained in a raster scan observation from SAS 3. These show the Lupus Loop to be a faint extended source of soft X-rays with a temperature about 2.5 million K. The most prominent feature of the region is the A.D. 1006 supernova remnant, which is unexpectedly bright at 0.2-1.0 keV. One speculative interpretation of the low-energy flux from SN 1006 is as blackbody radiation from a hot neutron star.

Winkler, P. F., Jr.↗
NASA NTRS1978

Comparison of high energy gamma rays from absolute value of b greater than 30 deg with the galactic neutral hydrogen distribution

High-energy gamma-ray (energy above 35 MeV) data from the SAS 2 satellite have been used to compare the intensity distribution of gamma rays with that of neutral hydrogen (H I) density along the line of sight, at high galactic latitudes (absolute values greater than 30 deg). A model has been constructed for the case where the observed gamma-ray intensity has been assumed to be the sum of a galactic component proportional to the H I distribution plus an isotropic extragalactic emission. A chi-squared test of the model parameters indicates that about 30% of the total high-latitude emission may originate within the Galaxy.

Ozel, M. E.↗
NASA NTRS1979

Galactic plane gamma-radiation

Analysis of the SAS 2 data together with the COS B results shows that the distribution of galactic gamma-radiation has several similarities to that of other large-scale tracers of galactic structure. The radiation is primarily confined to a thin disc which exhibits offsets from b = 0 degrees similar to warping at radio frequencies. The principal distinction of the gamma-radiation is a stronger contrast in intensity between the region from 310 to 45 degrees in longitude and the regions away from the center that can be attributed to a variation in cosmic-ray density as a function of position in Galaxy. The diffuse galactic gamma-ray energy spectrum shows no significant variation in direction, and the spectrum seen along the plane is the same as that for the galactic component of the gamma-radiation at high altitudes. The uniformity of the galactic gamma-ray spectrum, the smooth decrease in intensity as a function of altitude, and the absence of any galactic gamma-ray sources at high altitudes indicate a diffuse origin for bulk of the galactic gamma-radiation rather than a collection of localized sources.

Hartman, R. C.↗
NASA NTRS1977

X-ray burst sources

Current knowledge of sources of X-ray bursts, defined as having rise times of less than a few seconds, durations of a few seconds to a few minutes and a generally regular recurrence pattern, is reviewed. An examination of the galactic distribution of X-ray burst sources, which has been confirmed by SAS-3 rotating modulation collimator observations, reveals that the burst sources are spread along the galactic equator and clustered near low galactic longitudes, unlike the distribution of globular clusters. At least four X-ray burst sources have been associated with steady X-ray sources based on positional coincidence, and it has been found that the X-ray bursts are less intense but harder than steady X-ray emission from these sources. Individual burst sources, including MXB1659-29, which has not been identified with a steady X-ray source, the source in NGC6624 which has been identified with 3U1820-30, MXB1837+05, associated with Ser X-1, three burst sources near the galactic center and the rapid burster MXB1730-335 are briefly discussed.

Lewin, W. H. G.↗
NASA NTRS1979

Persistent emission from X-ray burst sources and the nature of galactic bulge X-ray sources

Intrinsic persistent emission from galactic bulge X-ray sources and the ratio of the average persistent X-ray luminosity to the time-averaged burst luminosity associated with Type I burst sources are discussed in the light of the thermonuclear flash model of X-ray burst emission. Values of the ratio between average persistent luminosity and time-averaged burst luminosity for a large collection of SAS 3 sources are presented to confirm the predictions of the burst model of thermonuclear flashes in freshly accreted matter on a neutron star. The model also predicts a critical value of the persistent accretion rate, below which bursts can occur. It is suggested that the galactic bulge X-ray sources represent neutron stars undergoing accretion, with burst sources accounting for a subset in which the accretion rate is below the critical value.

Van Paradijs, J.↗
NASA NTRS1979

The locations of X-ray sources in globular clusters

The SAS 3 X-ray observatory has been used to measure the positions of the X-ray sources in the globular clusters NGC 1851, 6441, 6624, 6712, and 7078. The derived positions have error circles with 90% confidence radii of 10 or 30 arcsec, which, in each case, include the optical center of the cluster. The results of a statistical analysis demonstrate that the X-ray sources are more concentrated toward the cluster centers than the visible stars and are therefore more massive than those stars.

Jernigan, J. G.↗
NASA NTRS1979

Discovery of a soft X-ray flux from AN Ursae Majoris

During November 1975, the soft X-ray detectors on the SAS 3 satellite scanned across AN Ursae Majoris, a star very similar to AM Herculis in its unusual optical properties. A soft (0.1-0.4 keV) X-ray flux averaging 2.8 x 10 to the -11th erg/sq cm-sec was detected from AN UMa, as had been anticipated by analogy with AM Her. Folding the X-ray flux measurement with the known binary period reveals an X-ray light curve with approximately 100% modulation, and thereby secures the identification of the X-ray source as AN UMa. Unlike the case in AM Her, the X-ray minimum in AN UMa occurs midway between optical linear-polarization peaks.

Hearn, D. R.↗
NASA NTRS1979

Steady X-ray emission from MXB 1730-335 /the Rapid Burster/

SAS 3 observations of the Rapid Burster, MXB 1730-335, in three energy channels between 1.3 and 12 keV are used to examine temporary enhancements of the steady X-ray flux from that source following very energetic (long) Type II X-ray bursts. It is found that the average steady X-ray enhancement apparently reaches a maximum value corresponding to about 40% of the time-averaged burst flux, that no significant change in the shape of the X-ray spectrum of the enhancement is evident from the data, and that a certain minimum time interval is needed to obtain enhanced steady emission. The enhanced steady X-ray emission is shown to amount to an average steady contribution of about 5% of the time-averaged burst flux. It is concluded that the observed correlation of the onset and termination of the enhancement with the occurrence of Type II bursts strongly supports the earlier suggestion that the Type II bursts from the Rapid Burster are caused by instabilities in the accretion of matter onto a compact object.

Van Paradijs, J.↗
NASA NTRS1979

Soft X-ray observation of the Rho Ophiuchus dark cloud region

Soft X-rays (0.1-0.8 keV) from the region including the Rho Oph dark cloud were observed with the SAS-3 low-energy X-ray telescope. No X-ray absorption by the cloud was observed. This indicates that the diffuse component of soft X-rays in this region is mostly from the foreground of the Rho Oph cloud which is located at a distance of 160-200 pc.

Apparao, K. M. V.↗
NASA NTRS1980

The apsidal motion test in 4U 0900-40

Recent SAS 3 observations of 4U 0900-40 have confirmed the apparent eccentricity of the orbit. Arguments are presented to show that the measured eccentricity is not a spurious effect resulting from systematic reflection of the X-ray beam within the binary system. The longitude of periastron is not observed to have advanced in the 3.5 years since its original determination. The limit on apsidal motion is omega not greater than 3.8 deg/yr which, in turn, restricts the apsidal motion constant to log k not greater than -2.5. These limits are used to constrain the physical parameters of the companion star HD 77581.

Rappaport, S.↗
NASA NTRS1980

X-ray maps of the Vela supernova remnant

X-ray maps of the Vela supernova remnant in two energy channels, 0.1-0.4 keV and 0.4-0.8 keV, are presented. The data were obtained in 1975 from a SAS 3 satellite observation. We describe the Wiener filter technique used to deconvolve the angular response of the instrument from the data. The X-ray structure is compared with the optical and radio features of the region.

Hearn, D. R.↗
NASA NTRS1980

Simultaneous X-ray and optical observations of rapid variability in Scorpius X-1

Copernicus and SAS-3 observations of Sco X-1 during very active states show strong and rapid X-ray flickering with time scales as short as 20 sec. Simultaneous optical photometry reveals similar and remarkably well correlated flickering of lower amplitude. The level of correlation decreases when the X-ray source becomes fainter, but optical and X-ray fluxes, averaged over 1 min, are usually well correlated for B magnitudes less than 12.9. Cross-correlation analysis of the data during periods of high activity shows no really significant time delay between X-ray and optical features, although the cross-correlation function peaks systematically for positive lag values (optical following X-rays). The amplitude of the X-ray flickering exhibits a strong energy-dependence consistent with the well-known intensity versus spectral-hardness relation derived from previous observations. The highly correlated optical activity is interpreted as due to reprocessing of X-ray photons in the binary system.

Ilovaisky, S. A.↗
NASA NTRS1979

Galaxies and gamma-ray astronomy

The nature of the high-energy spectra of several types of active galaxies and their contribution to the measured diffuse gamma-ray emission between 1 and 150 MeV are considered, using X-ray spectra of active galaxies and SAS 2 data regarding the intensity upper limits to the gamma-ray emission above 35 MeV. It is found that a substantial increase in slope of the photon energy spectrum must occur in the low energy gamma-ray region for Seyfert galaxies, BL Lac objects, and emission line galaxies; the power-law spectra observed in the X-ray range must steepen substantially between 50 keV and 50 MeV. In addition, a cosmological integration shows that Seyfert galaxies, BL Lac objects, and quasars may account for most of the 1-150 MeV diffuse background, even without significant evolution.

Bignami, G. F.↗
NASA NTRS1979

Deep X-ray survey of the Small Magellanic Cloud

An extended survey of the Small Magellanic Cloud with the SAS 3 X-ray observatory detected SMC X-1 but no other source with a luminosity greater than 1.0 x 10 to the 37th ergs/sec. In particular, SMC X-2 and SMC X-3, observed one month earlier at luminosities of 7 x 10 to the 37th and 10 x 10 to the 37th ergs/sec, respectively, were not detected, which proves that they are both highly variable. The results indicate that the maximum luminosities of early-type X-ray stars in the SMC congregate near 10 to the 38th ergs/sec, which is about five times the maximum luminosity of similar sources in the Galaxy.

Clark, G.↗
NASA NTRS1980

Observations of Cygnus X-3 with the Einstein /HEAO 2/ X-ray Observatory The period derivative and the asymmetric X-ray light curve

Cygnus X-3 was observed by the Monitor Proportional Counter on the Einstein (HEAO 2) X-ray Observatory for 2.4 days in 1978 December. The analysis of the data from these observations is used in conjunction with a self-consistent re-examination of previous results from the Uhuru, ANS, COS B, and SAS 3 satellites to investigate earlier reports that the 4.8 hour period of Cygnus X-3 is increasing. It is found that there is indeed a period derivative, P = (1.78 plus or minus 0.40) x 10 to the -9th s/s, which confirms the principal conclusion of previous authors. The possibility that the X-ray source is in an elliptical orbit and that some, or all, of the observed period derivative may be due to apsidal motion is discussed. The elliptic orbit hypothesis explains the observed asymmetry in the average X-ray light curve and leads to the conclusion that the most likely companion to the X-ray source is a helium star, possibly with a light hydrogen envelope

Elsner, R. F.↗
NASA NTRS1980

Observations of diffuse galactic gamma rays

Observations of 35 MeV to several GeV diffuse gamma radiation from the galaxy are available from the SAS-2 and COS-B instruments. This paper gives a brief review of the experimental problem, a discussion of the high-latitude (local) galactic component, and a study of the more distant low-latitude emission from the galactic plane. Finally, the emerging observations in other energy ranges are mentioned.

Simpson, G. A.↗
NASA NTRS1980

X-ray observations of 4U/MXB 1735-44

The paper discusses the SAS-3 X-ray observations of MXB 1735-44 during 1977-78. Fifty-three bursts were observed in 20 days, in irregular intervals from 2 to more than 50 hr. The irregular burst behavior of MXB 1735-44 may be caused by its high intrinsic X-ray luminosity. No correlations were found between burst frequency and properties of the associated persistent source, such as flux and hardness of the persistent spectrum. There may be a correlation between the size of the bursts and burst intervals: the bursts tend to be smaller when they occur more frequently. The distributions of the burst sizes in terms of their integrated burst flux and maximum burst flux have standard deviations of about 37%.

Lewin, W. H. G.↗
NASA NTRS1980

Observations of the Crab Nebula, NGC 4151, Cyg X1 and Cyg X3 at medium gamma ray energies

The paper analyzes observations of the Crab Nebula, NGC 4151, Cyg X1, and Cyg X3 taken with the UCR gamma ray telescope at a residual atmospheric depth of about 3.5 g/sq cm on a balloon launched from Palestine, Texas, 4.5 GV, 2000 local time LT (0100 UT), on September 29, 1978. The data consists of continuous observations from 0430 LT (0930 UT) on September 30 to 1800 LT (2300 UT) on October 1, 1979. A flux increase is observed at the right ascension of the Crab Nebula within about a 10 min uncertainty of telescope source position determination, eliminating the SAS-2, CG 195+4, and the two COS-B sources in the antigalactic center direction as the origin of the gamma rays. The total flux of gamma rays for the Crab Nebula from 1.2 to 10 MeV is (6.1 + or - 1.5) x 10 to the -3rd photons/sq cm-s, with an upper limit at 10-20 MeV of 7 x 10 to the -5th photons/sq cm-s. Results for the NGC 4151, Cyg X1, and Cyg X3 are also discussed and flux upper limits are given.

Zanrosso, E. M.↗