Search Publications
The Complex 0.4--12 keV X-Ray Spectrum of Cygnus X-1
van der Woerd, H.; Barr, P.
Simultaneous observations of the 0.4-2 keV and 2-12 low-state spectrum of Cygnus X-1, made with the low-energy transmission grating spectrometer and gas scintillation proportional counter on board EXOSAT, are presented. At least four spectral components are required to describe the data: a hard (energy spectral index alpha about 0.4) power law dom…
Analysis of the COS B Data for Evidence of Linear Polarization of VELA Pulsar Gamma Rays
Mattox, John R.; Mayer-Hasselwander, Hans A.; Strong, Andy W.
The COS B spark chamber telescope observations of the Vela pulsar were analyzed for gamma-ray polarization. No significant quadrupole moment is found in the azimuthal distribution of the electron-positron pair production planes. However, analysis of the sensitivity indicates that even 100-percent polarization would not be detected. Therefore, the …
The High-Luminosity BL Lacertae Object PKS 0823-22
Falomo, Renato
Simultaneous infrared, optical, and UV observations of the BL Lacertae object PKS 0823-22 are presented. The identification of the observed absorption doublet at λλ5341, 5355 with Mg II λλ2796, 2803 gives an absorption redshift z_abs_ = 0.910. At this redshift, the object is one of the most luminous of its class with M_V_ <~ -29.4. The spectral…
Detection of Trace Helium in G104-27, a 26,000 K DA White Dwarf
Wesemael, F.; Holberg, J. B.; Kidder, K. M.
The detection of the He I 4471 A feature in the moderately hot DA white dwarf G104 - 27 places this star within the rather sparse class of DAB white dwarfs. It does not appear possible, on the basis of the present data, to distinguish between a stratified and a homogeneously mixed atmosphere. While a stratified structure would be natural for a DA …
Small-Scale Structure in the Diffuse Interstellar Medium
Meyer, David M.
The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected …
Simultaneous X-Ray, Ultraviolet, and Optical Observations of LMC X-3
Maraschi, L.; Tanzi, E. G.; Belloni, T. +7 more
The black hole candidate LMC X-3 was observed simultaneously at X- ray (Ginga), UV (IUE), and optical frequencies in 1988 January. The X- ray energy distribution is the superposition of a thermal component and a hard tail. The former component can be described equally well by a Comptonization spectrum or by a disk blackbody. In the latter picture,…
Ultraviolet Observations of NGC 205
Bertola, Francesco; Wilcots, Eric M.; Hodge, Paul +2 more
Low-resolution IUE observations of the dwarf elliptical galaxy NGC 205 show that the UV spectral energy distribution of the galaxy is relatively flat. Spectra centered on the nucleus and on a region north of the nucleus show evidence of recent "bursts" of star formation which contribute strongly to the UV spectral energy distribution. We fit the U…
EXOSAT Observations of Cygnus X-2 Continuum and Line Spectrum
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +7 more
An analysis of five Exosat observations of Cyg X-2, taken around a full binary orbit is presented. The data were obtained using all instrumentation (1000 lines/mm Transmission Grating Spectrometer, Channel Multiplier Array + filters, Medium-Energy experiment, and Gas Scintillation Proportional Counter) simultaneously, and span the full energy rang…
X-Ray and Ultraviolet Observations of the Seyfert Galaxy MCG 8-11-11
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +4 more
MCG 8-11-11 was observed in the 0.5-8 keV band with the EXOSAT observatory at 9 epochs in 1983-1986. Quasi-simultaneous UV observations were obtained in all but one case. The X-ray spectra are well fitted by absorbed power laws (N_H_ ~ 1.5 x 10^21^ cm^-2^, α_ph_ ~ 1.7). Small variations of the spectral shape are found with softening of the source …
An Evolving Relativistic Jet Model for the BL Lacertae Object Markarian 421
Kondo, Y.; Urry, C. M.; Hutter, D. J. +2 more
Coordinated observations of the nearby BL Lacertae object Mrk 421 obtained during 1980 May, 1984 January, and 1984 March are described. These observations give a time-frozen picture of the continuous spectrum of Mrk 421 at X-ray, ultraviolet, optical and radio wavelengths. The observed spectra have been fitted to an inhomogeneous relativistic jet …