High energy X-ray observations of Cyg X-3 from OSO-8 - Further evidence of a 34.1 day period
(Previously announced in STAR as N82-18085)
Dolan, J. F.↗
Engineering topics
Dennis, B. R.
Publications and source records attributed to Dennis, B. R..
Time variations of an absorption feature in the spectrum of the gamma-ray burst on 1980 April 19
The photon number spectrum integrated over the impulsive part of the event is shown to fit a thermal bremsstrahlung function with a temperature of 330 + or - 70 keV at energies between 151 and 487 keV. At lower energies, the data points lie considerably below this function, indicating a broad absorption feature extending down to values less than or equal to 28 keV, the lowest energy measured. The upper energy of this absorption feature varies from 100 to 150 keV on a time scale less than or equal to 0.5 s. This event is interpreted as a typical gamma ray burst, even though it is still considered remotely possible that it is of solar origin. The spectral features, together with their variability, are interpreted in terms of electron interactions at the cyclotron resonance frequency in magnetic fields of 10 to the 12th - 10 to the 13th gauss close to the surface of a neutron star.
Dennis, B. R.↗
Fluorescent excitation of photospheric Fe K-alpha emission during solar flares
The Bent Crystal Spectrometer on the NASA Solar Maximum Mission satellite provides high spectral and temporal resolution observations of the Fe K-alpha lines. Analyses have been conducted of spectra from almost 50 solar flares that occurred during 1980. These data strongly support fluorescent excitation of photospheric iron by photons of E greater than 7.11 keV emitted by the hot coronal plasma produced during the flare. After comparison of the data with a model, the observed K-alpha line widths are discussed along with estimates of the size of the emitting region, the height of the coronal source and the photospheric iron abundance.
Parmar, A. N.↗
Properties of solar flare electrons, deduced from hard X-ray and spatially resolved microwave observations
An important question concerning an understanding of impulsive solar flares is related to the energetic electrons responsible for the microwave and the hard X-ray emission. A description is presented of an investigation in which spatially resolved microwave observations of an impulsive flare and hard X-ray data from the Solar Maximum Mission (SMM) are used to test the hypothesis that the two types of emission come from the same basic electron population. The considered observations are found to imply that the microwaves and hard X-rays were not produced by a common population of electrons with either a Maxwellian or single power-law energy distribution. It is suggested that the calculations should be repeated when observations of stronger events become available, for which a better determination of the X-ray spectrum is possible. The possibility is considered that microwaves and moderately hard X-rays come from spatially different regions.
Marsh, K. A.↗
High energy X-ray observations of CYG X-3 from from OSO-8: Further evidence of a 34.1 day period
The X-ray source Cyg X-3 (=4U2030+40) was observed with the high energy X-ray spectrometer on OSO-8 for two weeks in 1975 and in 1976 and for one week in 1977. No change in spectral shape and intensity above 23 keV was observed from year to year. No correlation is observed between the source's intensity and the phase of the 34.1 day period discovered by Molteni, et al. (1980). The pulsed fraction of the 4.8 hour light curve between 23 and 73 keV varies from week to week, however, and the magnitude of the pulsed fraction appears to be correlated with the 34.1 day phase. No immediate explanation of this behavior is apparent in terms of previously proposed models of the source.
Dolan, J. F.↗
The high energy X-ray spectrum of 4U 0900-40 observed from OSO 8
The X-ray source 4U 0900-40 (= Vela XR-1) was observed with the high-energy X-ray spectrometer on OSO 8 for one week in 1976 and three weeks in 1978. Spectra of the source are presented above 16 keV. No systematic difference exists between the X-ray eclipse centers and the eclipse centers predicted from optical ephermerides. Short period intrinsic variability in the system's X-ray intensity may be related to changes in the Compton scattering optical depth in the system and does not require sporadic mass transfer via Roche lobe overflow. The 282 s modulation in the source's X-ray flux above 21 keV consists of two essentially similar pulses per period, most easily interpreted as arising from the two different magnetic poles of a rotating neutron star. The secondary appears to be a spherically accreting, magnetic neutron star.
Dolan, J. F.↗
Concurrent radio, infrared, optical and X-ray observations of the nucleus of the Seyfert galaxy NGC 4151
The nucleus of the Seyfert galaxy NGC 4151 was observed during May and June 1977 at X-ray energies from 20 to 200 keV using the high-energy X-ray spectrometer on OSO 8 at radio frequencies of 2695 and 8085. Data were also taken in the visual, and at infrared wavelengths of 1 to 2 microns, and from 2 to 6 keV using the OSO 8 proportional counter. Optical data showed variability by a factor of 2 within the observing period, which is comparable to the variability in the 2 to 6 keV X-ray flux. No variability, however, was measured at infrared or radio frequencies. The composite spectrum from radio to gamma-ray is plotted, and it is found that the optical and X-ray fluxes varied during the observing period, although it is not known if they varied concurrently.
Beall, J. H.↗
Observations of solar flares on 1980 April 30 and June 7 with the hard X-ray burst spectrometer
Descriptions of hard X-ray observations for solar flares occurring on 1980 April 30 and June 7 are presented. The hard X-ray light curve for the June 7 event shows complex intensity variations on time scales of 100 ms and spectral variations on time scales of seconds. The results for the 1980 April 30 flare are compared with simultaneous observations from other SMM instruments and from ground-based observatories. These comparisons have enhanced the interpretation of the hard X-ray data for this event and have permitted the tentative identification of the origin of the hard X-ray emission with a small loop structure within the flare region.
Orwig, L. E.↗
The solar flare of 1980 March 29 at 0918 UT as observed with the hard X-ray burst spectrometer on the Solar Maximum Mission
Explore the source record for details and available documents.
Dennis, B. R.↗
The high energy X-ray spectrum of 4U 1700-37 observed from OSO 8
The most intense hard X-ray source in the confused region in Scorpius has been identified as 4U 1700-37 (=HD 153919). Observations extending over three binary periods in 1978 September were carried out with the high-energy X-ray spectrometer on OSO 8. The 3.4 day modulation is seen above 20 keV with the intensity during eclipse being consistent with zero flux. The photonumber spectrum from 20 to 150 keV is well represented by a single power law with a photonumber spectral index of -2.77 + or - 0.35 or by a thermal bremsstrahlung spectrum with kT = 27 (+15, -7)keV. The counting rate above 20 keV outside of eclipse shows no evidence for the 96.8 minute X-ray modulation previously reported at lower energies. Despite the difficulties that exist in reconciling both the lack of periodic modulation in the emitted X-radiation and the orbital dynamics of the system with our currently accepted theories of the evolution and physical properties of neutron stars, the observed properties of 4U 1700-37 are all consistent with the source being a spherically accreting neutron star rather than a black hole.
Dolan, J. F.↗
High energy X-ray and radio studies of Scorpius X-1
The results from extended high energy X-ray observations of Scorpius X-1 from the OSO 8 satellite are reported. The source was observed for a total of 15 days in 1975, 1977, and 1978. Simultaneous 10.7 GHz and 4.75 GHz radio data were obtained during the 1978 observation, and low energy X-ray data during the 1975 and 1978 observations. Detailed studies of the data reveal a lack of any correlation between the high energy X-rays and the other energy ranges. A 3 sigma upper limit of 22% was obtained for any modulation of the high energy flux with the binary period. No high energy tail was observed at any time.
Coe, M. J.↗
Detection of high-energy X-rays from the galactic center region
Results are presented from repeated scans of the galactic center region made with the high-energy X-ray detector on OSO 8 during the five days of Sept. 20-25, 1978. The observations show a strong flux of high-energy excluding GX 1 + 4 and GX 3 + 1. The photon-number spectrum of this flux is harder than that of GX 1 + 4 measured during the same interval.
Dennis, B. R.↗
The hard X-ray burst spectrometer on the Solar Maximum Mission
The paper considers the primary scientific objectives of the Hard X-ray Burst Spectrometer to be flown on the Solar Maximum Mission. The objectives are: (1) to determine mechanisms which accelerate electrons to 20-100 keV in the first stage of a solar flare and to more than 1 MeV in the second stage of many flares, and (2) to characterize the spatial and temporal relation between electron acceleration, storage, and energy loss throughout a solar flare. In the first year after launch, it is expected that about 1000 flares will be observed above the instrument threshold.
Orwig, L. E.↗
Detection of high energy X-rays from the galactic center region
Observations of the galactic center region made with the high energy X-ray detector on OSO-8 are discussed. A strong hard X-ray which was detected during these observations from the vicinity of the galactic center are examined. The counting rate spectrum and the photon number spectrum of the flux are determined. Comparisons with the high energy X-ray fluxes observed from sources in the region by others are discussed.
Dennis, B. R.↗
The High Energy X-ray Spectrum of 4U1700-37 Observed from OSO-8
The most intense hard X-ray source in the confused region in Scorpius is identified as 4U1700-37. The 3.4-day modulation is seen above 20 keV with the intensity during eclipse being consistent with zero flux. The photon-number spectrum from 20 to 150 keV is well represented by a single power law with a photo-number spectral index of -2.77 + or - 0.35 or by a thermal bremsstrahlung spectrum with kT = 27 96.8-min X-ray modulation previously reported at lower energies. Despite the difficulties in reconciling both the lack of periodic modulation in the emitted X-radiation and the orbital dynamics of the system with theories of the evolution and physical properties of neutron stars, the observed properties of 4U1700-37 are all consistent with the source being a spherically accreting neutron star rather than a black hole.
Dolan, J. F.↗
The hard X-ray burst spectrometer on the solar maximum mission
The primary scientific objective of the spectrometer is to provide a greater understanding of the role of energetic electrons in solar flares. This will be achieved by observations of high energy X-rays in the energy range from 20 to 200 keV with time resolution of 0.128s on a continuous basis and as short as 1 ms for limited intervals. The X-ray detector is an actively shielded CsI(Na) crystal with a thickness of 0.635 cm and a sensitive area of 71 sq cm. In the first year after launch, it is expected that approximately 1000 flares above the sensitivity threshold of 0.2 photons/(sq cm s) lasting for one second, will be detected.
Orwig, L. E.↗
The high-energy pulsed X-ray spectrum of Hercules X-1 as observed with OSO 8
Hercules X-1 was observed from August 30 to September 10, 1977, by using the high-energy X-ray scintillation spectrometer on board the OSO 8 satellite. The observation, during which the source was monitored continually for nearly an entire ON-state, covered the energy range from 16 to 280 keV. Pulsed-flux measurements as a function of binary orbit and binary phase are presented for energies between 16 and 98 keV. The pulsed flux between 16 and 33 keV exhibited a sharp decrease following the fourth binary orbit and was consistent with zero pulsed flux thereafter. Only weak evidence was found for temporal variation in the pulsed flux between 33 and 98 keV. The pulsed spectrum has been fitted with a power law, a thermal spectrum without features, and a thermal spectrum with a superposed Gaussian centered at 55 keV. The latter fit has the smallest value of chi-square per degree of freedom, and the resulting integrated line intensity is approximately 0.0015 photon/sec per sq cm for a width of 3.1 (+9.1, -2.6) keV. This result, while of low statistical significance, agrees with the value observed by Truemper (1978) during the same ON-state.
Maurer, G. S.↗
The 78.4-day period of Cygnus XR-1
Data from observations of Cyg XR-1 made by the high energy X-ray spectrometer on OSO 8 were analyzed together with previously reported (Dolan, 1977) observations of the polarization of HDE226868 in the U-band in an attempt to detect the 78.8-d modulation reported by Kemp et al. (1977, 1978) in the optical and low-energy X-ray wavelength region. No such modulation was found at the wavelengths studied. It is suggested that if such modulation does exist, it is more likely to be related to the rotation of the free modes of oscillation of the primary than to the existence of a third body in the system.
Dolan, J. F.↗