Engineering topics

Burrows, D. N.

Publications and source records attributed to Burrows, D. N..

53 records · Page 3

NASA NTRS1993

Probing the galactic halo with ROSAT

We discuss the current status of ROSAT shadowing observations designed to search for emission from million degree gas in the halo of the Milky Way galaxy. Preliminary results indicate that million degree halo gas is observed in the 1/4 keV band in some directions, most notably toward the Draco cloud at (l,b) = (92 deg, +38 deg), but that the halo emission is patchy and highly anisotropic. Our current understanding of this halo emission is based on a small handful of observations which have been analyzed to date. Many more observations are currently being analyzed or are scheduled for observation within the next year, and we expect our understanding of this component of the galactic halo to improve dramatically in the near future.

Burrows, D. N.↗

NASA NTRS1993

A multiwavelength study of the Eridanus soft X-ray enhancement

We present soft X-ray, N(H), and IR maps of the Eridanus soft X-ray enhancement. Soft X-ray maps from the HEAO 1 A-2 LED experiment, processed with a maximum entropy method (MEM) algorithm, show that the enhancement consists of two distinct components: a large hook-shaped component and a small circular component at different temperatures. Both of these are located in 'holes' in the IR emission, and they correspond to N(H) features at very different velocities. The dust surrounding the X-ray enhancements appears to be associated with several high-latitude molecular clouds, which allow us to obtain a probable distance of about 130 pc to the near edge of the main enhancement. The total power emitted by the hot gas is then about 10 exp 35 to 10 exp 36 ergs/s. We consider alternative interpretations of these objects as adiabatic supernova remnants or as stellar wind bubbles and conclude that they are more likely to be stellar wind bubbles, possibly reheated by a SN explosion in the case of the main, hook-shaped object.

Burrows, D. N.↗

NASA NTRS1992

The soft X-ray diffuse background observed with the HEAO 1 low-energy detectors

Results of a study of the diffuse soft-X-ray background as observed by the low-energy detectors of the A-2 experiment aboard the HEAO 1 satellite are reported. The observed sky intensities are presented as maps of the diffuse X-ray background sky in several energy bands covering the energy range 0.15-2.8 keV. It is found that the soft X-ray diffuse background (SXDB) between 1.5 and 2.8 keV, assuming a power law form with photon number index 1.4, has a normalization constant of 10.5 +/- 1.0 photons/sq cm s sr keV. Below 1.5 keV the spectrum of the SXDB exceeds the extrapolation of this power law. The low-energy excess for the NEP can be fitted with emission from a two-temperature equilibrium plasma model with the temperatures given by log I1 = 6.16 and log T2 = 6.33. It is found that this model is able to account for the spectrum below 1 keV, but fails to yield the observed Galactic latitude variation.

Garmire, G. P.↗

NASA NTRS1992

The AXAF CCD imaging spectrometer

The current status of the instrument design and the status of the CCDs being fabricated for the AXAF CCD Imaging Spectrometer (ACIS) are summarized. The instrument consists of an image recording array of CCDs and a linear arrangement of CCDs to record the spectra formed by the objective grating spectrometer. Both arrays employ CCDs with pixel dimensions which correspond to about 0.5 arcsec samples of the image. The CCDs provide moderate spectral resolution and good detection efficiency over the energy range 0.5 to 10 keV. Spectral resolution of 200 or more is achievable using the objective grating with the grating array. Radiation damage effects are shown to degrade the energy resolution of CCDs. Specially designed CCD pixel architecture is employed together with shielding and low temperature operation to slow the effects of radiation damage.

Garmire, G. P.↗

NASA NTRS1991

Charge coupled devices (CCDs) in X-ray astronomy

The application of CCDs to X-ray imaging and spectroscopy in astronomy is discussed with special attention given to the special requirements of CCDs for X-ray astronomy (as opposed to those for traditional optical applications). The development status of CCDs for X-ray astronomy applications is described, and results of recent research in the area of optimizing the CCD X-ray response are presented. It is shown that very high quantum efficiencies and Fano noise-limited energy resolutions can be obtained using CCDs.

Lumb, D. H.↗

NASA NTRS1989

Search for soft X-ray emission from SN 1987A with a CCD X-ray imaging spectrometer

The results of soft X-ray observations of SN 1987A over the energy band 0.65-2.0 keV are reported. The upper limits on the soft X-ray flux are inconsistent with an extrapolation of the spectrum measured by the Ginga Satellite to the energy band and require a turnover in the X-ray spectrum between 2 and 4 keV. If this turnover is due to absorption by intervening material, a neutral column density associated with the supernova of at least 2.8 x 10 to the 21st/sq cm is required. The background rate for the Texas Instruments 800 x 800 pixel CCD, measured between 150 and 285 km altitude, was 1.1 counts/sq cm s. The background spectrum has a broad peak at 350 electrons, corresponding to charge deposited in the detector by minimally ionizing particles.

Burrows, D. N.↗

NASA NTRS1989

Observational constraints on an embedded cloud model for the soft X-ray diffuse background

The reason for the observed anticorrelation between soft X-ray diffuse background (SXRB) and neutral hydrogen column densities are considered. Using the B and C band data from an all-sky survey of the SXRB, as well as data in the Be band, it is shown that the Jakobsen and Kahn (1986) embedded cloud model, in which several statistical properties of the SXRB in the B and C bands were used to constrain their model parameters, cannot fit the observed band ratios, except in the limit in which virtually all of the emission originates in the near side of the absorbing gas. It was also shown that model parameters corresponding to appreciably mixed emission and absorption, as proposed by Bunner et al. (1969) and Davidsen et al. (1972), do not fit the data. Model parameters corresponding to the absorption models of Bowyer et al. (1968), Bunner et al. (1969), Davidsen et al. (1972), and Yentis et al. (1972), cannot fit the data unless the absorbing material is more strongly clumped than is permitted by 21-cm observations.

Burrows, D. N.↗

NASA NTRS1987

A 9 month long soft X-ray survey of the Large Magellanic Cloud. I - X-ray map at 1/4 keV

Data from the HEAO 1 low energy detector was used to map the diffuse 1/4 keV X-ray background around the LMC. Data was collected over 9 mos in 1977-1978 using detectors sensitive in the range 0.18-2.8 keV. Diffuse emission, rather than absorption, was observed from the LMC, as were two large emission (2 million K) regions with very low surface brightness. The regions coincided with the Shapley III supergiant shell of optical nebulosity and the LMC bar. Higher spatial resolution imagery is required if the emission features are to be confirmed as the same type of phenomena as the X-ray superbubble in Cygnus.

Singh, K. P.↗

NASA NTRS1985

Soft X-ray maps of the Large Magellanic Cloud (LMC)

Soft X-ray maps of the Large Magellanic Cloud (LMC) were obtained from scanning-observations with the HEAO-1 low energy detectors. Comparison of the 1/4 keV X-ray observations with the neutral hydrogen column densities in the LMC obtained from a 21 cm line survey, shows no evidence for absorption effects in the 1/4 keV X-ray flux from the LMC due to the neutral matter in the LMC. Instead, faint X-ray emission is detected from the LMC. The extent of this emission is smaller than the size of the halo or the disk of the LMC. Assuming this 1/4 keV emission to be diffuse, it is identified with a supergiant shell of optical nebulosity known as Shapley III, and the bar of the LMC. The X-ray luminosities of the regions are estimated to be 9 times 10 to the 38th power ergs/sec and 1.8 times 10 to the 39th power ergs/sec for the Shapley III region and the bar of the LMC respectively. Shapley III could be an X-ray superbubble.

Singh, K. P.↗

NASA NTRS1984

Limits on soft X-ray flux from distant emission regions

The all-sky soft X-ray data of McCammon et al., and the new N sub H survey (Stark et al.) was used to place limits on the amount of the soft X-ray diffuse background that can originate beyond the neutral gas of the galactic disk. The X-ray data for two regions of the sky near the galactic poles are shown to be uncorrelated with 21 cm column densities. Most of the observed X-ray flux must therefore originate on the near side of the most distant neutral gas. The results from these regions are consistent with X-ray emission from a locally isotropic, unabsorbed source, but require large variations in the emission of the local region over large angular scales.

Burrows, D. N.↗

NASA NTRS1984

Local Contributions to the 0.6 Kev Diffuse X-ray Background

The intensity of the X-ray background between 0.5 and 1.0 keV has surprisingly little dependence on galactic latitude. Possible mechanisms for the production of these X-rays include extragalactic emission and emission from dM stars, both of which should be strongly dependent on galatic latitude, and diffuse emission from hot gas (T approx. = 3 x 10 to the 6th power K) surrounding the Sun. These mechanisms can be distinguished by the presence or absence of absorption by gas within a few hundred parsecs of the Sun. X-ray data from the HEAO-1 LED detectors and H1 data from the recent Crawford Hill 21 cm survey are used to place limits on the 0.6 keV intensity originating within 300 pc of the Sun in the general direction of (lambda,b) = (150 deg - 30 deg).

Burrows, D. N.↗

NASA NTRS1984

Limits on soft X-ray flux from distant emission regions

The all-sky soft X-ray data of McCammon et al. and the new N sub H survey (Stark et al. was used to place limits on the amount of the soft X-ray diffuse background that can originate beyond the neutral gas of the galactic disk. The X-ray data for two regions of the sky near the galactic poles are shown to be uncorrelated with 21 cm column densities. Most of the observed x-ray flux must therefore originate on the near side of the most distant neutral gas. The results from these regions are consistent with X-ray emission from a locally isotropic, unabsorbed source, but require large variations in the emission of the local region over large angular scales.

Burrows, D. N.↗

NASA NTRS1983

The soft X-ray diffuse background

Maps of the diffuse X-ray background intensity covering essentially the entire sky with approximately 7 deg spatial resolution are presented for seven energy bands. The data were obtained on a series of ten sounding rocket flights conducted over a seven-year period. The different nature of the spatial distributions in different bands implies at least three distinct origins for the diffuse X-rays, none of which is well-understood. At energies of approximately 2000 eV, an isotropic and presumably extragalactic 500 and 1000 eV, an origin which is at least partially galactic seems called for. At energies 284 eV, the observed intensity is anticorrelated with neutral hydrogen column density, but we find it unlikely that this anticorrelation is simply due to absorption of an extragalactic or halo source. Previously announced in STAR as N83-20892

Mccammon, D.↗

NASA NTRS1983

Possible contributions of supernova remnants to the soft X-ray diffuse background (0.1 - 1 keV)

Almost all of the B band (0. 10-0.19 keV) and C band (0.15-0.28 keV) X-rays probably originate in a hot region surrounding the sun, which Cox and Anderson modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5-1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra galactic power law flux and any large-scale-height stellar (or galactic halo) emission.

Sanders, W. T.↗

NASA NTRS1982

Possible contributions of supernova remnants to the soft X-ray diffuse background (0.1 - 1keV)

Almost all of the B band (0.10-0.19 keV) and C band (0.15-0.28 keV) X-rays probably originate in a hot region surrounding the Sun, which Cox and Anderson modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5-1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra galactic power law flux and any large-scale-height stellar (or galactic halo) emission.

Sanders, W. T.↗

NASA NTRS1982

The soft X-ray diffuse background

Maps of the diffuse X-ray background intensity covering essentially the entire sky with approx. 7 deg spatial resolution are presented for seven energy bands. The data were obtained on a series of ten sounding rocket flights conducted over a seven-year period. The different nature of the spatial distributions in different bands implies at least three distinct origins for the diffuse X-rays, none of which is well-understood. At energies or approx. 2000 eV, an isotropic and presumably extraglalactic 500 and 1000 eV, an origin which is at least partially galactic seems called for. At energies 284 eV, the observed intensity is anticorrelated with neutral hydrogen column density, but we find it unlikely that this anticorrelation is simply due to absorption of an extragalactic or halo source.

Mccammon, D.↗

NASA NTRS1979

Spatial distribution and broad-band spectral characteristics of the diffuse X-ray background, 0.1 - 1.0 keV

Preliminary maps covering more than 85 percent of the sky are presented for three energy bands: the B band, the C band, and the M band. The study was undertaken to find evidence that most of the diffuse X-ray background at energies less than 1 keV is local to the galaxy and that it is most probably due to thermal radiation from a low density plasma which fills a substantial fraction of interstellar space. A preliminary analysis of the data is provided including a report that most of the B and C band flux has a common origin, probably in a 10 to the 6th power K region surrounding the Sun, and that most of the M band flux does not originate from the same material.

Mccammon, D.↗