Engineering topics

Coe, M. J.

Publications and source records attributed to Coe, M. J..

33 records · Page 2

NASA NTRS1980

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.↗

NASA NTRS1980

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.↗

NASA NTRS1979

High energy X-ray observations of Sco-like sources with Ariel V

Results are reported for observations of Sco X-1 and the similar sources 4U 1702-36 (GX 349+2, Sco X-2), 4U 1813-14 (GX 17+2), and 4U 1758-25 (GX 5-1) by several of the X-ray telescopes aboard the Ariel 5 satellite over the energy range from 2 to approximately 100 keV. The results confirm the existence of a high-energy tail in the spectrum of Sco X-1, demonstrate that 4U 1702-36 has a similar spectrum, and provide evidence for a variation of the 26-56-keV flux from 4U 1702-36 by more than a factor of four with no related change in the 2.9-7.6-keV flux. The high-energy emission from Sco X-1 is found to be one to two orders of magnitude above the extrapolated low-energy emission. Observed X-ray, radio, and optical properties of these four sources, as well as two additional Sco-like sources, are summarized.

Greenhill, J. G.↗

NASA NTRS1979

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.↗

NASA NTRS1979

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.↗

NASA NTRS1979

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.↗

NASA NTRS1979

X-ray observations of AM Herculis from OSO 8

X-ray observations of the white dwarf binary system AM Herculis in the range 2 to 250 keV, taken by OSO 8, are presented and compared with balloon and Ariel 5 measurements. The composite spectrum of the 2 to 40 and 20 to 250 keV fluxes determined by the proportional counter and the high energy scintillation spectrometer, respectively, on board the satellite is shown averaged over the entire binary cycle. Variations in spectral shape and intensity between the OSO 8 results and balloon measurements taken 10 to 20 days apart are observed. Results indicate the presence of a spectral break at about 15 keV on some occasions, similar to that seen in Her X-1, however presumably caused by a different mechanism than in the neutron star. It is also considered unlikely that the gamma-ray tail observed by Ariel 5 existed during OSO 8 observations.

Coe, M. J.↗

NASA NTRS1979

The 78.4 day period of Cygnus XR-1

A search for a 78.4 day modulation in the high energy X-ray flux observed with OSO-8 and in the U-band optical polarization is reported. It is suggested that if such a 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.↗

NASA NTRS1979

High energy X-ray observations of BL lacertae objects

BL Lac objects are of considerable current interest both because they were recently realized to be a new class of objects and because they were found to be similar in many significant respects to QSOs and Seyfert Galaxies. Since at least one model for the X-ray emission predicts a flattening of the X-ray spectrum above a few keV, several of these sources were studied using the high energy scintillation telescopes on OSO-8 and Ariel-5. With the possible exception of Markaryan 421, only upper limits were obtained for the X-ray emission in the energy ranges 25-60 and 60-130 keV, thereby imposing constraints on any spectral breaks.

Coe, M. J.↗

NASA NTRS1979

X-ray observations of AM Herculis from OSO-8

The white dwarf binary system AM Herculis (2A1815+500) was observed in X-rays at both low energies (E less 10 keV) and higher energies. The exact shape of the spectrum, particularly at the higher energies, has yet to be determined. Results from the high energy scintillation spectrometer on OSO-8 are presented. These are combined with results published elsewhere obtained concurrently with the proportional counter on the same satellite, thereby giving for the first time coincident observations of AM Her over the range 2 to 250 keV.

Coe, M. J.↗

NASA NTRS1979

High energy X-ray observations of BL Lacertae objects

Several BL Lacertae objects were observed at energies above 25 keV using the scintillation telescopes on OSO-8 and Ariel-5. With the possible exception of Markaryan 421, only upper limits were obtained for the existence of X-ray emission in the energy ranges 25-60 and 60-130 keV. These results impose constraints on any flattening in the X-ray spectrum of BL Lac objects as predicted by at least one model for their X-ray emission.

Coe, M. J.↗

NASA NTRS1978

The high-energy pulsed X-ray spectrum of HER X-1 as observed with OSO-8

Her X-1 was observed from 1977 August 30 to September 10 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. The pulsed spectrum was 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 - squared per degree of freedom, and the resulting integrated line intensity is 1.5 superscript + 4.1 subscript - 1.4 x .001 photons s superscript-1 cm superscript-2 for a width of 3.1 superscript + 9.1 subscript -2.6 keV. This result, while of low statistical significance, agrees with the value observed by Trumper (1978) during the same On-state.

Maurer, G. S.↗

NASA NTRS1978

The X-ray source Serpens X-1 - Ariel 5 observations and discussion of models for the spectrum and time variability

Experimental data from Ariel 5 on the spectral shape and time variability of Ser X-1 are presented, and possible explanations for the observations are discussed in terms of current theoretical suggestions for source emission. The observations are summarized in the form of a light curve for 3-7.6-keV photons. The data are fitted with a power law of index -2.3, which yields a hydrogen column density of (1.1 + or - 0.4) x 10 to the 22nd power atoms/sq cm. No persistent periodicity of amplitude greater than 5% of the steady flux is found, but evidence of statistically significant burst activity is obtained. Various emission mechanisms are considered for the time-averaged spectrum and the X-ray bursts. It is suggested that the inverse Compton mechanism is a likely cause for the emission from this source and that the source is radiating near the Eddington limit.

Coe, M. J.↗

NASA NTRS1978

High energy X-ray and radio studies of Scorpius X-1

The results from extended high energy X-ray observations of Scorpius XR-1 from the OSO-8 satellite are reported here. 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. The data reveals a lack of any correlation between the high energy X-rays and the other energy ranges. A three standard deviation 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.↗

NASA NTRS1977

The high energy X-ray detector on the Ariel-5 satellite

The Imperial College hard X-ray detector which is used to make spectral measurements in the 26 keV to 1.2 MeV energy range on celestial X-ray sources from the Ariel-5 satellite is described. Details are given of the design, calibration and in-orbit performance of the detector. A modulation process is used to detect weak signals against a background and we give details of the spectrum unfolding techniques used to convert the measured spectra into corrected incident spectra.

Engel, A. R.↗