Engineering topics

Serlemitsos, P. J.

Publications and source records attributed to Serlemitsos, P. J..

At least 55 records · Page 3

NASA NTRS1980

Is the remnant of SN1006 crab-like?

The solid state spectrometer on the Einstein Observatory and the GSFC cosmic X-ray spectrometer on OSO-8 observed the X-ray spectrum of SN1006. The data can be well-represented by a power-law model with alpha = 1.2, similar to the spectrum of the Crab nebula. This is in contrast to the radio and X-ray maps of SN1006 which show a shell structure more typical of SNR with thermal X-ray emission. The X-ray spectrum is suggestive of nonthermal synchrotron emission, raising the possibility that the remnant of SN1006 contains a source of relativistic electrons.

Becker, R. H.↗

NASA NTRS1980

Variable X-ray spectra of BL Lac objects: HEAO-1 observations of PKS 0548-322 and 2A 1219+305

X-ray spectra for the BL Lac objects PKS 0548-322 and 2A 1219+305 measured with the HEAO-1 A2 detectors during pointing maneuvers on September 30, 1978 and May 31, 1978 respectively are presented. Both fit single power law components with low energy absorption. For 2A 1219+305, a thermal bremsstrahlung form gives an unacceptable fit. From a comparison with other statistically poorer observations taken at 6 month intervals while the satellite was in its normal scanning mode, it is found that the sources exhibit spectral variability. A summary of measurements of the 5 BL Lac objects detected with the A2 experiment is presented and it is concluded that X-ray spectral changes in this class of source are common. Their general X-ray spectral characteristics distinguish BL Lac objects from other classes of X-ray emitting active galactic nuclei. Analysis of their total spectra indicates that most of the energy is emitted in the 5 to 100 eV band.

Worrall, D. M.↗

NASA NTRS1980

X-ray and ultraviolet spectroscopy of Cygnus X-1 = HDE 226868

Observations of Cygnus X-1 with the solid-state spectrometer on the Einstein Observatory are presented. The X-ray spectra of two intensity dips viewed near superior conjunction did not exhibit increased photoelectric absorption. Rather, the data support a model in which an increase in the electron-scattering optical depth modifies both the observed spectrum and the intensity. The characteristic temperature of the intervening material is greater than about 50 million K. These measurements were in part simultaneous with observations by IUE. The ultraviolet spectrum and intensity remained relatively constant during an X-ray intensity dip.

Pravdo, S. H.↗

NASA NTRS1980

X-ray spectrum of Kepler's supernova remnant

Observations made with the Solid State Spectrometer (SSS) aboard the Einstein Observatory confirm Kepler's SNR as an X-ray source with an intensity between 1 and 3 keV of 7.2 x 10 to the -11th ergs/sq cm s. The X-ray spectrum is similar to those of Cas A and Tycho, with strong line emission from the helium-like species of Si, S, and Ar. Direct comparisons to Tycho's SNR suggest a distance to Kepler's SNR of not less than 5 kpc.

Becker, R. H.↗

NASA NTRS1980

The HEAO A-2 survey of Abell clusters and the X-ray luminosity function

The HEAO A-2 all sky data base was surveyed for 2-10KeV X-rau emission from the 225 Abell clusters og galaxies listed in Abell's (1958) catalog which are of distance class four or less, and are within the fraction of the sky surveyed completely by Abell. Thirty-two identifications of clusters with X-ray sources were made, for which 2-10 KeV fluxes and 90% error boxes are presented. Twelve of these identification are new. The X-ray luminosity function was derived for this statistically complete sample and the best exponential fit was found to be f(L) = 20.2 x 10 to the minus 8 power exp (-l(44)/1.9) per cu Mpc 2-10KeV. The relationship between X-ray luminosity and richness was examined and a correlation was found for richness classes 0, 1, and 2. The relationship of X-rau luminosity, Bautz-Morgan type, and Rood-Sastry type was examined. It was found that BM type I's and RS type cD and B have the greatest average luminosity. The contribution of clusters to the X-ray background was calculated from the luminosity function and was found to be 5%, and with 90% certainty, less than 8% in the 2-10 KeV band pass.

Mckee, J. D.↗

NASA NTRS1980

X-ray observations of Algol

Observations of Algol using a solid state spectrometer onboard the Einstein Observatory are discussed. Two observations six months apart were made, both during a primary optical eclipse. No corresponding X-ray eclipses were seen. During the second observation the source was flaring and was on average a factor three brighter. The spectrum on both occasions was consistent with a two-component thermal equilibrium model with temperatures of approximately 7.5 and 40 million degrees. Attempts to insert a third component indicate the temperature distribution to be bimodal. Models for the X-ray emission are discussed and it is suggested that the emission most likely originates from an active corona surrounding the K star.

White, N. E.↗

NASA NTRS1980

X-ray and UV spectroscopy of Cygnus X-1 = HDE226868

Observations are presented of Cygnus X-1 with the solid-state spectrometer on the Einstein Observatory. The X-ray spectra of two intensity dips viewed near superior conjunction did not exhibit increased photoelectric absorption. Rather the data support a model in which an increase in the electron scattering optical depth modifies both the observed spectrum and the intensity. The characteristic temperature of the intervening material is greater than 5 x 10 to the 7th power K. These measurements were in part simultaneous with observations by IUE. The ultra violet spectrum and intensity remained relatively constant during an X-ray intensity dip.

Pravdo, S. H.↗

NASA NTRS1980

The X-ray spectrum of QSO 0241+622

Proportional counters on the OsO-8 spacecraft measured the X-ray spectrum of QSR 0241+622 in the range 2-50 keV. The best power law fit has a proton spectral index and 90 percent errors gamma = 1.93 (+0.5, -0.3) and low energy absorption consistent with reported gas column densities, but a thermal bremsstrahlung form with temperature 13.1 keV cannot be excluded. No indication of spectral variability is found in three observations of the source with HEAO-A2, although a possible 15-30 percent intensity change over a period of 6 months was observed. The quasar is similar to 3C 273 in the proportion of energy emitted in various bands, excluding the radio, if reported radiation above 50 keV from its direction is indeed associated with QSO 0241+622. The two quasars are compared and possible energy generation scenarios are discussed. Implications concerning quasar contributions to the diffuse background are discussed.

Worrall, D. M.↗

NASA NTRS1980

HEAO 1 spectra of X-ray emitting Seyfert 1 galaxies

The paper presents the 2-50-keV X-ray spectra and time variability information on seven Seyfert 1 galaxies NGC 3783, NGC 4151, NGC 5548, NGC 6814, MK 509, MCG 8-11-11, and ESO 141-G55, obtained with the A2(2) experiment on HEAO 1. It is concluded that the spectra of Seyfert 1 galaxies can be well represented by flat power laws of high-temperature thermal breamsstrahlung models with relatively low column densities.

Mushotzky, R. F.↗

NASA NTRS1980

The X-ray pulsars 4U1145-61 and 1E1145.1-6141

Observations of the X-ray sources near 4U1145-61 are presented. The presence of two periodicities at 291 and 297 seconds is confirmed. The location of the shorter period is isolated to within 3 arc minutes of 4U1145-61. The spectrum of 4U1145-61 is a power law out to at least 60 keV with a 500 eV EW iron line at 6.7 keV. The inferred spectrum of the other is absorbed. No evidence is found for a monotonic variation in either pulse period.

White, N. E.↗

NASA NTRS1980

X-ray spectrum of Kepler's SNR

Observations made with the solid state spectrometer aboard the Einstein Observatory confirm Kepler's SNR as an X-ray source with an intensity between 1-3 KeV of 7.2 x 10 to the-11th power ergs/sq cm-s. The X-ray spectrum is similar to those of Cas A and Tycho, with strong line emission from the helium-like species of Si, S, and Ar. Direct comparisons to Tycho's SNR suggest a distance of Kepler's SNR of greater than or equal to 5 kpc.

Becker, R. H.↗

NASA NTRS1980

The diffuse X-ray background spectrum from 3 to 50 keV

The spectrum of the extragalactic diffuse X-ray background has been measured with the GSFC Cosmic X-ray Experiment on HEAO 1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane. A total exposure of 80 sq m-s-sr is available at present. Free-free emission from an optically thin plasma of 40 plus or minus 5 keV provides an excellent description of the observed spectrum from 3 to 50 keV. This spectral shape is confirmed by measurements from five separate layers of three independent detectors. With an estimated absolute precision of about 10%, the intensity of the emission at 10keV is 3.2 keV/keV/sq cm/s/sr, a value consistent with the average of previously reported spectra. A uniform hot intergalactic medium of approximately 36% of the closure density of the universe would produce such a flux, although nonuniform models indicating less total matter are probably more realistic.

Marshall, F. E.↗

NASA NTRS1980

Elemental abundances in a Type I supernova remnant

The solid-state spectrometer (SSS) on the HEAO 2 (Einstein) X-ray observatory observed the X-ray spectrum of Tycho's SNR. The observations show a relative excess of line emission from Si, S, and Ar by not less than 6 compared to that expected from a plasma of solar composition in collisional equilibrium and by a factor of not less than 3 compared to Cas A. Similar excesses are not found for line emission from Mg and Fe. The data suggest that the SN observed by Tycho in 1572 produced significant amounts of Si group elements but did not eject large amounts of Fe as predicted by some models of Type I SN events.

Becker, R. H.↗

NASA NTRS1979

X-ray line emission from Capella

X-ray emission-line components from Mg, Si, S, and Fe are unambiguously detected from Capella with the solid-state spectrometer onboard the Einstein Observatory. The X-ray spectrum is inconsistent with an isothermal corona, and requires components between 6-million K and at least 24-million K for an adequate fit. An inhomogeneous corona in which the X-ray emitting plasma is confined to magnetically contained loops appears to be reconcilable with all of the experimental evidence.

Holt, S. S.↗

NASA NTRS1979

X-ray spectrum of Cassiopeia A measured with the Einstein SSS

The solid state spectrometer (SSS) on the Einstein Observatory observed the X-ray spectrum of Cas A between 0.8 and 4.5 keV with a FWHM energy resolution of 160 eV. Line emission consistent with transitions of helium-like ions of Si, S, and Ar was well defined. Comparison between the data and the emission expected from a gas containing two distinct thermal components requires additional line emission from Mg, Al, Ca, and Fe. These results are discussed in the context of both equilibrium and nonequilibrium situations.

Becker, R. H.↗

NASA NTRS1979

HEAO 1 observation of a type I burst from MXB 1728-34

Results are presented for an analysis of data on a type I X-ray burst from MXB 1728-34 observed by three large-area instruments on HEAO 1. The measurements cover the energy range from 2 to 150 keV and provide the capability of resolving significant intensity variations on a time scale of milliseconds and spectral changes on a scale of tenths of seconds. The initial rise of the burst is discussed, millisecond intensity variations are examined, and the spectral evolution of the burst is described. Physical parameters are estimated for various source models, and the total X-ray flux at energies of 85 to 180 keV during the burst is shown to have been no more than about 6% of the total observed X-ray flux at energies below 25 keV.

Hoffman, J. A.↗

NASA NTRS1979

Large-scale structure of X-ray clusters of galaxies

Observations from the A-2 experiment on HEAO-1 are used to search for very large-scale structure (exceeding a degree) in 40 X-ray sources in clusters of galaxies. Significant evidence for extension is found only in the relatively nearby Perseus and Virgo clusters. For the remainder of the sources the results place stringent limits on the flux in any very large component.

Nulsen, P. E. J.↗

NASA NTRS1979

Long-term studies with the Ariel 5 ASM. II - The strong Cygnus sources

The three bright 3-6 keV X-ray sources in Cygnus are examined for regular temporal variability with a 1300 day record from the Ariel 5 All-Sky Monitor. The only periods consistently observed are 5.6 days for Cyg X-1, 11.23 days for Cyg X-2, and 4.8 hours for Cyg X-3. The 78.4 day period of Kemp, Herman, and Barbour for Cyg X-1, the 9.843 day period of Cowley, Crampton, and Hutchings for Cyg X-2, and the 16.75 day period of Holt et al. for Cyg X-3 are not confirmed.

Holt, S. S.↗