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  • 11
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    EGRET detection of high energy gamma rays from the gamma-ray burst of 3 May 1991 (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: On May 3, 1991, the Energetic Gamma Ray Experiment Telescope on the Compton Gamma Ray Observatory detected a gamma-ray burst both in the energy measurement subsystem and independently in the spark chamber assembly. Six individual photons were detected in the spark chamber, allowing a determination of the burst arrival direction which was l(II) = 171.9 deg +/- 1.3 deg, b(II) = 5.3 deg +/- 1.1 deg. Three energy spectra were measured from 1 to 200 MeV; they were measured during the first second after the Burst and Transient Sources Experiment trigger, the next two seconds, and the subsequent four seconds. The first two spectra exhibit a similar differential spectra index of about -2.2 with no apparent high-energy cut-off. By the time of the third spectrum, an additional soft component is evident.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 255; 1-2; p. L13-L16.
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  • 12
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    The Galactic halo and local intergalactic medium toward PKS 2155-304 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Low-resolution UV observations of the bright, low-redshift BL Lac object PKS 2155-304 have been obtained by the HST's high-resolution spectrograph. Attention is here given to results on the number of intergalactic H I Ly-alpha components in the line-of-sight toward this object. The highest-redshift of the observed Ly-alpha systems furnishes a lower limit on the distance of the BL Lac object; this distance is consistent with the approximate redshift deduced from CCD imagery of the probable host galaxy for PKS 2155-304.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 409; 1; p. 199-204.
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  • 13
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    Constraints on the cosmic rays in the Small Magellanic Cloud (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Observations of the SMC using the Energetic Gamma Ray Experimental Telescope (EGRET) on the Compton Observatory are reported. The findings yield an upper limit for gamma-ray emission above 100 MeV of 0.5 x 10 exp -7 photon/sq cm s. The expected flux if the cosmic rays (CR) are universal rather than Galactic in origin is (2.4 +/- 0.5) x 10 exp -7 photon/sq cm s, only a third of which arises from cosmic ray electron interactions. Thus, the bulk of the CR energy density is almost certainly neither metagalactic nor universal, but Galactic in origin. The results add to the evidence that the SMC is in a nonequilibrium state and indicate that the LMC is most likely in quasi-stable equilibrium, with a CR energy density near the maximum that can be contained.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 70; 2; p. 127-129.
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  • 14
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    Evidence for evolution of the luminosity function of clusters of galaxies (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: From an all sky, X-ray flux limited sample of clusters of galaxies evidence for a significant deficit in the number of high luminosity clusters is found in the redshift range z approximately 0.1 to 0.2 compared with numbers of nearby clusters. This indicates that the X-ray luminous clusters are undergoing strong evolution. The strength of the effect is consistent with hierarchical merging models. The implications of such strong evolution for clusters are discussed.
    Keywords: ASTROPHYSICS
    Type: In: After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990 (A93-23605 07-90); p. 343-346.
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  • 15
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    Egret detection of the blazar PKS 0420-014 (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: During its full-sky survey, the Energetic Gamma Ray Experiment Telescope (EGRET) high-energy instrument aboard the Compton Gamma-Ray Observatory detected gamma-ray emission in the energy range above 30 MeV from a source identified as the blazar PKS 0420-014. This object was observed during two separate viewing periods in 1992 February/March and May/June. An intensity decrease above 100 MeV of a factor of at least 1.5 from a maximum of (5.0 +/- 1.4) x 10(exp -7) photons 1 sq cm/s was observed during that time interval indicating extensive variability. The photon spectrum in the range between 30 and 10,000 MeV at the time of the maximum intensity is well represented by a power law with an exponent of -1.9 +/- 0.3. Some similarities with other EGRET detected blazars are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 2; p. 659-662
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  • 16
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    Correlated hard X-ray and ultraviolet variability in NGC 5548 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Contemporaneous X-ray (from the Ginga satellite) and ultraviolet (IUE) observations of NGC 5548 in 1989-1990 show that the 1350 A and 2-10 keV flux both varied by a factor of 2.6 in a highly correlated fashion. Adding an additional simultaneous IUE-Exosat observation from 1984 significantly weakens the correlation, since the UV flux was 3.5 times larger then than its average 1990 value, while the X-ray flux was only 70 percent higher. In 1990 the UV and X-ray flux variations appear to be simultaneous to within no more than six days. These results, together with the simultaneity of the variations at 5000 and 1350 A, are incompatible with the standard geometrically thin accretion model. They may be explained, however, if part of the UV and optical radiation originates from reprocessing of X-rays emitted above the disk. Thus essentially all the UV flux in 1990 would be due to reprocessing. But the large UV outburst in 1984 probably represents a genuine increase in the disk throughput due to instability in the disk itself. The similar relationship between UV and X-ray emission in NGC 4151 suggests that this scheme may be applicable to Seyfert galaxies as a class.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 393; 1, Ju
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  • 17
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    Pulsed high-energy gamma-radiation from Geminga (1E0630 + 178) (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The detection of pulsed gamma rays with energy above 50 MeV from the soft X-ray source 1E0630 + 178 is reported, confirming the identification of Geminga with this X-ray source. The period derivative (11.4 +/- 1.7) x 10 exp -15 s/s suggests that Geminga is a nearby isolated rotating neutron star with a magnetic field of 1.6 x 10 exp 12 gauss, a characteristic age of 300,000 yr, and a spin-down energy loss rate of 3.5 x 10 exp 34 erg/s.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 357; 6376,; 306
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  • 18
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    First detection of line emission from the hot interstellar medium with solid state detectors (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Previously reported enhanced soft X-ray emission from the North-Galactic Polar region supports the theory of a hot interstellar component. This paper reports the first detection of line emission from the hot interstellar component in the North-Galactic-Polar region. Measurements were made with solid state Si(Li) detectors aboard a spin-stabilized rocket launched from the White Sands Missile Range on March 22, 1980. Two features are clearly present in the low energy portion of the spectrum derived from the data. They correspond to emission lines from C V (300 eV) and C VI (360 eV), and from O VII (560 eV) and O VIII (650 eV). The detection of emission lines coming from these highly stripped ions is direct evidence for the thermal origin of the emission and confirms the presence of a hot (1-million K) component in the interstellar medium.
    Keywords: ASTROPHYSICS
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  • 19
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    The dust coma of Comet Austin (1989c1) (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Thermal-infrared (10 and 20 micron) images of Comet Austin were obtained on UT 30.6 Apr., 1.8, 2.8, and 3.6 May 1990. The NASA-Marshall Space Flight Center 20 pixel bolometer array at the NASA 3 meter Infrared Telescope Facility in Hawaii was used. The 10.8 micron (FWHM = 5.3 microns) maps were obtained with maximum dimensions of 113 arcsec (57,500 km) in RA and 45 arcsec (23,000 km) in declination, with a pixel size of 4.2 x 4.2 arcsec. A smaller, 45 x 18 arcsec, map was obtained in the 19.2 micron (FWHM = 5.2 microns) bandpass. At the time of these observations Comet Austin's heliocentric and geocentric distances were 0.7 and 0.5 AU respectively. The peak flux density (within the brightest pixel) was 23 + or - 2 Janskys for the first three dates and only marginally lower the last day; i.e., within the observational uncertainties no evidence was found for day-to-day variability like that observed in Comet Halley. A dynamical analysis of the morphology of the extended dust emission is used to constrain the size distribution and production rate of the dust particles. The results of this analysis are compared with similar studies carried out on comets P/Giacobini-Zinner, P/Brorsen-Metcalf, P/Halley, P/Tempel 2, and Wilson (1987).
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Abstracts for the International Conference on Asteroids, Comets, Meteors 1991; p 35
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  • 20
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    Stripping of gas and dust from the elliptical galaxy M86 (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Past observations of the x ray morphology of M86 have revealed that the galaxy is experiencing ram-pressure stripping due to its large velocity (1500 km s(-1)) relative to the intracluster medium of Virgo (Forman et al. 1979, Fabian, Schwartz, and Forman 1980). Observations indicate that the x ray emitting gas in the plume of M86 is still being produced from the continual heating of gas and dust stripped from nearer the galaxy's center. Researchers obtained two-dimensional Infrared Astronomy Satellite (IRAS) images of M86 which have revealed that there are two spatially separated regions of emission, one at 60 microns and the other at 100 microns of the IRAS wavebands. The 100 microns emission, presumably from cool dust (at approximately 20 K), appears to be located near the center of the galaxy together with HI (detected by Bregman, Roberts and Giovanelli 1988), while the 60 microns emission appears to lie more than 3 arcminutes away from the optical center in a direction slightly south of the center of the plume. Optical images produced by scanning U.K. Schmidt plates, reveal asymmetric isophotal contours along the major axis of the galaxy (first reported by Nulsen and Carter in 1987, which they propose as excess emission due to star formation). This excess optical emission is co-incident with the direction of the 60 micron infra-red emission.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers; p 201-202
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