scholarly journals A balloon-borne X-ray survey of the central region of the galaxy

1968 ◽  
Vol 46 (10) ◽  
pp. S444-S447 ◽  
Author(s):  
Elihu Boldt ◽  
Henry Doong ◽  
Peter Serlemitsos ◽  
Guenter Riegler
Keyword(s):  
Central Region ◽  
Proportional Counter ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cesium Iodide ◽  
X Rays ◽  
Scintillation Crystal ◽  
X Ray ◽  
Gas Proportional Counter ◽  
The Galaxy

A balloon-borne X-ray survey of the galactic plane in the region of the galactic center was made from Australia during December 1966. The photon events recorded by a detector composed of a krypton gas proportional counter and a cesium iodide scintillation crystal are used to determine the spectrum of hard X-rays from the vicinity of Sgr XR-1.

scholarly journals Soft X-rays from the Galaxy

1970 ◽  
Vol 37 ◽  
pp. 406-407
Author(s):  
M. J. Rees
Keyword(s):  
Galactic Plane ◽  
Galactic Latitude ◽  
X Rays ◽  
Indirect Methods ◽  
X Ray ◽  
Background Data ◽  
Diffuse Background ◽  
The Galaxy ◽  
X Ray Background ◽  
Significant Flux

Below 1 keV, analyses of X-ray background data are complicated by galactic absorption effects, which cause the received intensity to vary with galactic latitude. Bowyer et al. (1968) observed that the diffuse background did not fall off as rapidly as was expected towards the galactic plane. One plausible interpretation of their data would be to suppose that a significant flux of soft X-rays emanates from the disc itself. I wish to discuss what could be inferred about the latter component from improved observations of its latitude-dependence, and by indirect methods.

scholarly journals Galactic plane structure in hard X-rays

2009 ◽  
Vol 5 (H15) ◽  
pp. 809-809
Author(s):  
A. Lutovinov ◽  
M. Revnivtsev ◽  
R. Krivonos
Keyword(s):  
Energy Band ◽  
Galactic Plane ◽  
Galactic Disk ◽  
X Rays ◽  
X Ray ◽  
The Galaxy ◽  
Increased Sensitivity ◽  
Using Data

AbstractWe study the structure of the Galaxy in the hard X-ray energy band (¿20 keV) using data from the INTEGRAL observatory. The increased sensitivity of the survey and the very deep observations performed during six years of the observatory operation allow us to detect about a hundred new sources. This significantly enlarges the sample of hard X-ray sources in the Galactic disk and bulge in a comparison with the previous studies.

scholarly journals Hot Plasma in the Galaxy

1998 ◽  
Vol 188 ◽  
pp. 47-50
Author(s):  
S. Yamauchi
Keyword(s):  
Galactic Plane ◽  
Point Sources ◽  
X Rays ◽  
Temperature Plasma ◽  
X Ray ◽  
X Ray Imaging ◽  
Hot Plasma ◽  
The Galaxy ◽  
Bulge Region ◽  
Imaging And Spectroscopy

In the X-ray band, we can see weak and extended X-rays along the Galactic plane and near the Galactic Bulge region, although these regions are dominated by many point sources (e.g., Warwick et al. 1985). The Tenma satellite discovered conspicuous emission lines from selected regions near the Galactic plane (Koyama et al. 1986). These lines are identified with K-shell line from He-like Fe, hence the extended emission is attributable to optically thin hot plasmas with temperatures of several keV. The origin of the thin hot plasmas, however, have been debatable, because no class of X-ray objects shows such high temperature plasma emissions. To investigate the origin of the extended X-rays, we are currently observing the Galactic plane regions with the ASCA satellite. In this paper, we report on the ASCA results: the hard X-ray imaging and spectroscopy of the hot plasma in the Galaxy.

scholarly journals Optical and Radio Information

1968 ◽  
Vol 1 ◽  
pp. 206-209
Author(s):  
Hugh M. Johnson
Keyword(s):  
Cross Sections ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Optical Data ◽  
X Rays ◽  
Interstellar Gas ◽  
X Ray ◽  
The Galaxy ◽  
Ionization Cross Sections ◽  
Optical Astronomy

The six or eight optically identified X-ray sources comprise starlike objects and extended supernova remnants in the Galaxy, well as as a radio galaxy and a quasar. Both X-ray and radiofrequency radiation penetrate the entire galactic plane, but only two or three galactic radio sources have been identified with X-ray sources. This has led Hayakawa et al. to postulate that detectable X-ray sources are not farther than 1 kpc. However, other studies suggest that there is a cluster of a few intrinsically bright sources actually near the galactic nucleus and a scattering of weaker sources near the sun.The distances of X-ray sources can be estimated from extinction by interstellar gas or intergalactic gas on spectra above 10 Å, but the method ultimately depends on the radio and optical data of the gas. Conversely, interstellar densities of certain elements with large photo-ionization cross-sections may be determined from the absorption of X-rays, after calibration of source distances by the methods of optical astronomy.

scholarly journals Hard Cosmic X-Ray Sources

1973 ◽  
Vol 55 ◽  
pp. 51-73 ◽  
Author(s):  
L. E. Peterson
Keyword(s):  
Supernova Remnants ◽  
Galactic Center ◽  
Galactic Plane ◽  
Crab Nebula ◽  
X Rays ◽  
X Ray ◽  
Sky Survey ◽  
Upper Limits ◽  
Observational Status ◽  
The Crab Nebula

A review of the observational status of X-ray sources detected in the 20 ⋍ 500 keV range is presented. Of the approximately 115 sources listed in the March 1972 edition of the UHURU 2–6 keV sky survey catalog, about 15 sources have been studied in hard X-rays. Most of the data have been obtained from balloons, although the OSO-3, and more recently the OSO-7, have contributed. With the exception of CEN A, the SMC, and possibly M-87, all the sources detected at higher energies are galactic and heavily concentrated in the galactic plane. The Crab Nebula has been measured to about 500 keV in continuous emission and a component at the ⋍ 33 ms pulsar period comprising about 20% of the total emission has been detected to ∼10 MeV. Objects such as SCO-1 and CYG-2 are characterized by an exponential spectrum, which varies over a 10 min. time scale about a factor of two, and a flatter spectrum extending to above 40 keV which exhibits independent variability. Objects such as CYG-1 and possibly CYG-3 have a multi-component power law spectrum extending to over 100 keV, and may vary many factors over a period of weeks. Other sources generally not yet identified with optical or radio candidates, located in the Galactic Center and the Centaurus/Crux region also show considerable variability, and in one case may have been detected to nearly 500 keV. Only upper limits at about 2 × 10−4 photon (cm2 s keV)−1 in the 20–50 keV range exist for most supernova remnants and extragalactic sources.

scholarly journals Interstellar absorption of X-rays emitted by supernova remnants

1970 ◽  
Vol 37 ◽  
pp. 134-137
Author(s):  
P. Gorenstein ◽  
E. M. Kellogg ◽  
H. Gursky
Keyword(s):  
Supernova Remnants ◽  
Galactic Center ◽  
Crab Nebula ◽  
A Priori ◽  
Time Interval ◽  
Short Time Interval ◽  
X Rays ◽  
X Ray ◽  
The Galaxy ◽  
Cas A

An X-ray observation of the Cassiopeia Region by the ASE group from a sounding rocket on December 5, 1968, has resulted in the determination of locations for two sources that are precise to about 0.1 of a square degree. The positions of two well-known radio sources Cas A and SN 1572 (Tycho's Supernova), objects which are remnants of relatively recent galactic supernova, are consistent with these locations. Inasmuch as that region of the galaxy does not appear to contain nearly as large a concentration of objects as the galactic center, it is reasonable to make the identification between the X-ray sources and the supernova remnants on the basis of there being a small a priori probability of having an accidental coincidence within 0.1 square degrees. Cas A is almost certainly the same source as Cas XR-1 which the NRL group saw in an earlier survey [1]. During the December flight the Crab nebula was also observed for a short time interval.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

scholarly journals ‘Local’ Theories of the X-Ray Background

1973 ◽  
Vol 55 ◽  
pp. 258-275 ◽  
Author(s):  
James E. Felten
Keyword(s):  
Intergalactic Medium ◽  
Galactic Plane ◽  
Cosmic Ray ◽  
Seyfert Galaxies ◽  
X Rays ◽  
Statistical Fluctuations ◽  
Galactic Emission ◽  
Diffuse Background ◽  
The Galaxy ◽  
X Ray Background

Recent theories of the origins of diffuse-background X-rays are reviewed, with emphasis on theories of the soft flux in the galactic plane and at the poles. This is probably partly galactic and partly extragalactic in origin. Failure to observe absorption by the Small Magellanic Cloud and by galactic gas in neighboring directions may be due to sources in the Cloud and to statistical fluctuations in galactic emission and absorption. Several models for numerous low-luminosity sources in the Galaxy are available. True ‘diffuse’ emission seems unnecessary. Absorption by Galactic gas seems to agree roughly with theory. The soft extragalactic component may arise in a hot intergalactic medium.The existence of a ‘diffuse’ galactic-plane excess in 1–100 keV is in some doubt. Low-luminosity sources may contribute to this as well.For isotropic X-rays in 1 keV – 1 MeV, superposition theories involving clusters of galaxies, Seyfert galaxies, etc. over a cosmological path length are now roughly viable. Simple ‘metagalactic’ Compton theories seem excluded if the break at 40 keV is sharp, but this is now in doubt. A very hot intergalactic medium at T ≈ 3 × 108 K would give the possibility of a sharp break.A recent upper limit on the line source strength of 100-MeV photons in the galactic plane may create some difficulties for cosmic-ray theory. The spectral shape of π-γ photons has become a matter of theoretical dispute.

scholarly journals Absorption and Production of Soft X-Rays in the Galaxy

1973 ◽  
Vol 55 ◽  
pp. 235-249
Author(s):  
S. Hayakawa
Keyword(s):  
Emission Lines ◽  
Interstellar Matter ◽  
X Rays ◽  
Diffuse Component ◽  
Number Density ◽  
High Number Density ◽  
Hard Component ◽  
X Ray ◽  
Cygnus Loop ◽  
The Galaxy

The column densities of interstellar hydrogen to X-ray sources derived from their spectra are compared with those obtained from 21 cm radio observations. Referring to several observed results on Cyg X-2, Cygnus Loop etc., the interpretation of the low energy cut-off of the spectrum in terms of the interstellar absorption is subject to ambiguities due to a modification of the emission spectrum by Compton scattering in the sources and the contribution of emission lines.The result of soft X-ray sky surveys indicates that the diffuse component of soft X-rays consists of the extragalactic and the galactic components. The former has a hard component with a power law spectrum and a soft component which may be represented by an exponential spectrum. The galactic component is so soft that its spectrum may also be explained by thermal bremsstrahlung of temperature of about 0.1 keV. Its generation rate may account for the heating and ionization of interstellar matter. It is suggested that galactic diffuse soft X-rays are produced by active stars of a rather high number density.

scholarly journals Measurements of Isotopic Abundances in Interstellar Clouds

1980 ◽  
Vol 87 ◽  
pp. 397-404 ◽  
Author(s):  
Arno A. Penzias
Keyword(s):  
Molecular Clouds ◽  
General Framework ◽  
Galactic Center ◽  
Galactic Plane ◽  
Giant Molecular Clouds ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
Isotopic Abundances ◽  
Si Isotopes

While an examination of the available data reveals some seemingly contradictory results, a general framework having the following outlines can be put forward:1. With the exception of the two galactic center sources SgrA and SgrB, the relative isotopic abundances exhibited by the giant molecular clouds in our Galaxy exhibit few, if any, significant variations from the values obtained by averaging the data from all these sources.2. The 13C/12C and 14N/15N abundance ratios are ∼130% and ∼150%, respectively, of their terrestrial values throughout the galactic plane and somewhat higher, ∼300%, near the galactic center.3. The 16O/18O and 17O/18O abundance ratios are ∼130% and ∼160%, respectively, of their terrestrial values throughout the Galaxy, although the former may be somewhat lower near the galactic center.4. The S and Si isotopes have generally terrestrial abundances.

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