Engineering topics

Swank, J. H.

Publications and source records attributed to Swank, J. H..

At least 55 records · Page 3

NASA NTRS1988

The 1981 outburst of the old nova GK Persei

Old nova GK Per was observed in 1981 with the IUE, during its rise, maximum, and subsequent return to minimum. In outburst, GK Per is luminous but much redder than dwarf novae or standard model accretion disks. The observed spectrum can be explained qualitatively with the Ghosh and Lamb (1979) model for the interaction of an accretion disk with the magnetic field of the accreting white dwarf. The N V and He2 are enhanced relative to other emission lines during outburst. This can be understood with photoionization by very soft X-rays having a luminosity comparable to that of the hard X-rays.

Wu, C.-C.↗

NASA NTRS1988

X-ray spectral models of Galactic bulge sources - The emission-line factor

Current difficulties in finding unique and physically meaningful models for the X-ray spectra of Galactic bulge sources are exacerbated by the presence of strong, variable emission and absorption features that are not resolved by the instruments observing them. Nine Einstein solid state spectrometer (SSS) observations of five Galactic bulge sources are presented for which relatively high resolution objective grating spectrometer (OGS) data have been published. It is found that in every case the goodness of fit of simple models to SSS data is greatly improved by adding line features identified in the OGS that cannot be resolved by the SSS but nevertheless strongly influence the spectra observed by SSS.

Vrtilek, S. D.↗

NASA NTRS1986

EXOSAT observations of V471 Tauri - A 9.25 minute white dwarf pulsation and orbital phase dependent X-ray dips

New results obtained from a 28 hr continuous observation of V471 Tauri with the EXOSAT satellite are reported. The detection of soft X-ray fluxes from both the white dwarf and the K dwarf, the discovery of a 9.25 minute pulsation from the white dwarf, and the discovery of orbital phase-related soft X-ray dips are discussed. The dips may be correlated with the triangular Lagrangian points of the binary orbit. The X-ray flux from the white dwarf is consistent with thermal models for a white dwarf photosphere with T(eff) of about 35,000 K, log g = 8.0-8.5, and log N(H) = 18.65 + or - 0.2.

Jensen, K. A.↗

NASA NTRS1986

Fast transients - A search in X-rays for short flares, bursts, and related phenomena

The HEAO 1 A-2 database on fast high energy X-ray transients was examined for any discernible regularities. The data were taken over the interval 1977-79 with six collimated multiwire, multilayer, proportional counters that had a sensitivity sufficient for detecting events lasting 1-5 sec at energies as low as 8-120 keV. The entire sky was surveyed completely three times in the observational period. Best-fit position, error box corners, mean transient flux and quiescent flux data are provided for all six of the type 3 events that were found. All the sources were within the Galaxy. The duration of the events ranged from 60-2000 sec. The limited number of events observed leads to estimates of 10,000-200,000 events per year. It is suggested that all the events originate from hard flares occurring at a rate of 20,000/yr on dMe/dKe stars.

Connors, A.↗

NASA NTRS1985

Coronal Temperatures

The solid state spectrometer (SSS) on the Einstein Observatory (HEAO 2) was sensitive in the energy range 0.5 to 4.5 keV to fluxes as low as 4x10 to the 12th power ergs/cu cm/s. Good spectra were obtained for 19 stars, including Algol, 7 RS CVn systems, 2 dMe stars, 2 W UMa binaries, 1 GV single star, and 3 0B supergiants, 2 BV stars and 1 07 binary. This is a very incomplete survey of stellar coronae, but it does include coverage of several late and early types and usually more than 1 sample of the class. The results for these stars suggest two generalizations despite the small numbers: (1) there is a broad variety of X-ray spectra of stellar coronae; and (2) there probably are X-ray spectral types (X-ray coronae of stars of similar other properties have similar temperatures). Evidence indicating that some emission distributions are bimodal is discussed. Finally, some remarks are made concerning the spectra of the early type stars and constraints on the presence of very high temperatures.

Swank, J. H.↗

NASA NTRS1985

The mass transfer rate in X1916-053 - It is driven by gravitational radiation?

A 50-minute period for a binary system harboring an X-ray burster would allow several alternatives for the mass-giving secondary, including an H-shell burning-plus-He degenerate core composite model. The burst properties of X1916-053 are presently used to argue against the He degenerate as well as the He main sequence solutions and to estimate whether, for any of the other solutions, the mass transfer rate could be consistent with that expected from gravitational radiation (GR). Within an uncertainty of a factor of 2, the transfer rate for the composite model solution is consistent with gravitational radiation, but enhancement by other mechanisms should be investigated.

Swank, J. H.↗

NASA NTRS1984

The 41.5 day binary X-ray pulsar 4U 1223 - 62 (GX 301 - 2)

Ariel 5 and SAS 3 X-ray pulse timing data for the 700 s X-ray pulsar 4U 1223 - 62 (GX 301 - 2) are reexamined in order to deduce the orbital elements of this system. The Ariel 5/SAS 3 arrival times are first reanalyzed to obtain the best solution for an orbital period close to 41.5 days and to estimate the uncertainties in it caused by unknown variations in the underlying pulse period. Spectral measurements by OSO 8 and HEAO 1 at a variety of orbital phases are presented and the origin of an unabsorbed, unpulsed soft component is discussed. OSO 8 observations of occasions when the amplitude and shape of the pulse profile changed dramatically are discussed. The global X-ray properties of the system are explained in terms of a simple stellar wind accretion model, and the interaction of the inflowing material with the neutron star magnetosphere is considered.

White, N. E.↗

NASA NTRS1984

Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

Phenomenological fits to the hard X-ray spectrum of AM Hercules have failed to explain the high equivalent width (0.8 + or - 0.1 keV) of Fe K-alpha emission. The scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base are investigated using the Monte Carlo method. It is shown that the Fe emission equivalent width observed in the spectrum of AM Her can be explained without resorting to an overabundance of Fe in the accreting material. For sufficient optical depth across the accretion column, equivalent widths of K-alpha emission even larger than the observed values can be obtained. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values.

Swank, J. H.↗

NASA NTRS1984

IUE observations of Centaurus X-4 during the 1979 May outburst

Ultraviolet spectrophotometry of the X-ray transient/burst source Centaurus X-4 at several intervals during the peak and decay of the May 1979 X-ray transient event was obtained. The spectrum was characterized by a blue continuum with alpha = 0.0 + or - 0.3 (F/nu/ varies as nu to the alpha power) and strong emission lines of N V lambda 1240, C IV lambda 1550, and Si IV lambda 1398. The relative intensities of the emission lines and the ratio of line to continuum strengths remained nearly constant during the decline. The emission lines may have arisen from a 'disk chromosphere', from X-ray heating of the K4 V companion star, or both. The ultraviolet data are combined with previously published optical and X-ray data to determine some of the physical characteristics of the system and to show that X-ray reprocessing plays an important role in producing the optical and ultraviolet continua.

Blair, W. P.↗

NASA NTRS1984

MXB 1916-053/4U 1915-05 - Burst properties and constraints on a 50 minute binary secondary

Results are presented from OSO-8 and HEAO-1 A2 observations of 34 bursts from the X-ray burster MXB 1916-053/4U 1915-05 recently discovered to show a 50 minute binary period. While 11 burst previously reported all had similar light curves, 22 observed two years later show a factor of 3 range of peak fluxes and decay times between 3 and 20 s. Recurrence times betweeen successive bursts vary between 3 and 6 hours. A ratio of steady flux to average burst flux of equiv 120 is developed. A burst observed with the HEAO-1 A2 experiment showed an initial temperature rise to a peak black body temperature of equiv 3 keV followed by the cooling typical of type I bursts. The burst was unusual in that the apparent projected size of a blackbody source increased by a factor of 3 during the cooling phase. Previously announced in STAR as N83-34872

Swank, J. H.↗

NASA NTRS1983

Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

Phenomenological fits to the hard X-ray spectrum of AM Herculis left unexplained the high equivalent width (0.8 + or - 0.1 keV) of Fe K alpha emission. A purely thermal origin implies a much steeper spectrum than was observed. With Monte Carlo calculations, scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base were investigated. The strength of the iron emission and the flat spectral continuum can be explained by the effects of fluorescence and absorption within the accretion column and the surface of the white dwarf on a thermal X-ray spectrum. Thomson optical depths across the column in the range 0.2 to 0.7 are acceptable. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values. Estimates of the column size differ by a factor of 40. Small spot sizes and low luminosities would be consistent with the soft component being the expected reprocessed bremsstrahlung and cyclotron radiation, although the constraint of matching the spectrum confines one to solutions with fluxes exceeding 20% the Eddington limits.

Swank, J. H.↗

NASA NTRS1983

X-ray spectra of Orion OB supergiants

The spectra are at a higher energy resolution than earlier X-ray observations of OB supergiants, and this allows stronger constraints to be placed on the location of the emission source in the outer atmosphere. The spectra of all three stars are found to be consistent with thermal sources which are only slightly attenuated by stellar wind opacity and have temperatures of approximately 10 to the (6.5 + or - 0.2) power K. A number of explanations of the soft X-ray flux distributions of early-type stars are tested. A model with the X rays coming only from a corona in a slab at the base of the wind does not seem a possibility unless the ionization or density structure of the overlying material is significantly different from that usually assumed for a cool wind. A model where the X rays are produced by radiatively driven shocks, some of which must be strong, can explain the X-ray luminosity and satisfy upper limits on the absorption by oxygen derived from the data. A high-energy (greater than 1 keV) contribution from a base coronal zone is considered possible. The spectrum of Zeta Ori shows emission near 2 keV, wich can be interpreted as line emission of Si XIII and S XV from a very hot source component with T = 1.5 x 10 to the 7th K.

Cassinelli, J. P.↗

NASA NTRS1983

The MXB1916-053/4U1915-05: Burst properties and constraints on a 50 minute binary secondary

Results are presented from OSO-8 and HEAO-1 A2 observations of 34 bursts from the X-ray burster MXB1916-053/4U1915-05 recently discovered to show a 50 minute binary period. While 11 burst previously reported all had similar light curves, 22 observed two years later show a factor of 3 range of peak fluxes and decay times between 3 and 20 s. Recurrence times between successive bursts vary between 3 and 6 hours. A ratio of steady flux to average burst flux of equiv 120 is developed. A burst observed with the HEAO-1 A2 experiment showed an initial temperature rise to a peak black body temperature of equiv 3 keV followed by the cooling typical of type I bursts. The burst was unusual in that the apparent projected size of a blackbody source increased by a factor of 3 during the cooling phase.

Swank, J. H.↗

NASA NTRS1983

Accretion powered X-ray pulsars

The current theoretical understanding of the properties of X-ray pulsars is assessed through a comparison with unified descriptions of 14 such systems, extending over six orders of magnitude in luminosity, in whose phase averaged spectra the only notable trend is a less abrupt high energy cutoff in the lower luminosity systems. Detailed pulse phase spectroscopy is given for five of the systems. A reexamination of the pulse phase spectra of 4U 0115 + 63 has uncovered electron cyclotron lines at 11.5 and 23 keV that appear to be in absorption at pulse peak and in emission during an interpulse. Spectral hardening regions such as those from Her X-1 are a common feature in the low energy pulse of many pulsars, and may represent the passage of the magnetic axis through the observer's line of sight. Attention is given to the nature of the beaming from Her X-1, and it is concluded that a pencil beam configuration represents the simplest explanation of the overall properties of the pulse.

White, N. E.↗

NASA NTRS1983

The X-ray absorption spectrum of 4U 1700-37 and its implications for the stellar wind of the companion HD 153919

The first high resolution non-dispersive 2-60 keV X-ray spectra at 4U1700-37 is presented. The continuum is typical of that found from X-ray pulsars; that is a flat powr law between 2 and 10 keV and, beyond 10 keV, an exponential decay of characteristic energy varying between 10 and 20 keV. No X-ray pulsations were detected between 160 ms and 6 min with an amplitude greater than approximately 2 percent. The absorption measured at binary phases approximately 0.72 is comparable to that expected from the stellar wind of the primary. The gravitational capture of material in the wind is found to be more than enough to power the X-ray source. The increase in the average absorption after phi of approximately 0.5 is confirmed. The minimum level of adsorption is a factor of 2 or 3 lower than that reported by previous observers, which may be related to a factor of approximately 10 decline in the average X-ray luminosity over the same interval. Short term approximately 50 percent variations in adsorption are seen for the first time which appear to be loosely correlated with approximately 10 min flickering activity in the X-ray flux. These most likely originate from inhomogeneities in the stellar wind of the primary. Previously announced in STAR as N83-14034

White, N. E.↗

NASA NTRS1983

Ultraviolet observations of the transient X-ray sources A0535 + 26 and A0620-00

Observations of A0535+26 (HDE 245770) by the ANS in September 1975 and March 1976 when it was at the X-ray low state are discussed. Also observed were 58 early-type stars lying within 10 deg of HDE 245770; these stars are used to derive a localized extinction curve. On the basis of the depth of the 2200 A interstellar absorption feature observed in the ANS flux distribution of HDE 245770 and the shape of the localized extinction curve, an E(B-V) = 0.72 is derived for HDE 245770. Observations were made of this system during its X-ray flare-up (October 1980) and quiescent (November 1981) states by the IUE. It is noted that the fine error sensor on board the IUE detected an increase in the optical brightness of HDE 245770 during the X-ray outburst. This greatly corroborates the identification of HDE 245770 as the optical counterpart of A0535+26. No significant change in the absorption-line profiles during the X-ray high and low periods is found, indicating that there was no significant increase in the stellar wind density when the X-ray flare-up occurred. The UV continuum level increased by less than 6 percent when it was near peak X-ray luminosity. The UV spectrum of HDE 245770 suggests that it is a B0 V or a B0 III star with its dereddened continuum slope slightly in favor of being a giant.

Wu, C.-C.↗

NASA NTRS1983

X-ray properties of the Be/X-ray system 28 0114+650 = LSI +65deg 010

Results are presented from experiments on the Einstein Observatory, HEAO 1, and OSO 8 on the temporal and spectral properties of 2S 0114+650. In a 12 hr Einstein monitor proportional counter and solid state spectrometer observation, two episodes of flaring occurred by an order of magnitude over about 1 hr. Variability on shorter time scales showed a preferred period of 14.9 minutes, but periodic pulsations were not seen in the HEAO 1 and OSO 8 data. The spectra above 1 keV were typical of accreting X-ray pulsars; the power law was E exp -alpha with alpha of about 1.2 for the number spectrum up to a cutoff at 14 keV. There is some evidence that the spectrum is steeper when the source is quiescent at low luminosity, but no large spectral changes attended the flares. Absorption column densities were consistent with interstellar reddening of the proposed companion, the Be star LSI +65 deg010. In the minute and hour variability and in the spectral character, 2S0114+650 is similar to other Be star-neutron star binary X-ray sources. Variations over several days in the OSO 8 data suggest orbital effects.

Koenigsberger, G.↗

NASA NTRS1982

X-ray properties of the Be/X-ray systems 2S0114+650 = LSI+65 deg 010

Results are presented from experiments on the Einstein Observatory, HEAO-1 and OSO-8 on the temporal and spectral properties of 2S0114+650. In a 12 hour Einstein MPC and SSS observation two episodes of flaring occurred by an order of magnitude over about 1 hour. Variability on shorter time scales showed a preferred period of 14.9 minutes, but periodic pulsations were not seen in the HEAO-1 and OSO-8 data. There is some evidence that the spectrum is steeper when the source is quiescent at low luminosity, but no large spectral changes attended the flares. Absorption column densities were consistent with interstellar reddening of the proposed companion, the Be star LSI+65 deg 010. In the minute and hour variability and in the spectral character, 2S0114+650 is similar to other Be star-neutron star binary X-ray sources. Variations over several days in the OSO-8 data suggest orbital effects.

Koenigsberger, G.↗