Galactic Column Research Articles

Analysis of soft X-ray excesses of quasi-stellar objects by using their IPC spectra

In the present paper, we have constructed a soft X-ray excess (SXE) sample from the sample of strong soft X-ray QSOs of Wilkes and Elvis (WE sample) by selecting those with column densities N H less than the galactic column densities N HG . By adopting a model such that the X-ray spectral index is linearly dependent on the energy (ILDE model) instead of the pure power-law (PPL) model, we have obtained for most of the sources N H ≥N HG so N H has got a physical meaning as the total effective hydrogen column density

THE REDDENING TO THE GALAXY IC 342 FROM CCB BV PHOTOMETRY OF ITS BRIGHTEST STARS

ABSTRACT The intrinsic luminosity and distance to the low-galactic-latitude galaxy IC 342 have been a matter of some debate, largely due to the uncertainty in the estimates for the extinction. The dynamical influence of IC 342 on the Local Group may be more significant than has commonly been believed if a high reddening value and a low distance modulus to this galaxy is confirmed. In an effort to independently estimate the reddening for this galaxy, CCD BV photometry has been obtained for 117 stars brighter than V=22.0 mag in a field centered near a spiral arm in IC 342. The plume of main sequence and slightly evolved blue supergiant stars is detected at V=19.4 mag. However, the plume is centered at a color of (B-V)=0.54 mag. A comparison with similar color-magnitude diagram data for the brightest stars in IC 1613 suggests that these stars in IC 342 are reddened by E(B-V)=0.79 ± 0.05 mag. (AB=3.32 ± 0.21 mag). This value is in good agreement with the similarly high values suggested by the Burstein-Heiles conversions of Galactic HI column density to color excess, and especially by the recent measurement of the Balmer decrement of HII regions by McCall.

GINGA and EXOSAT observations of the Perseus cluster of galaxies

Observations of the Perseus cluster of galaxies made using the Ginga and EXOSAT satellites are presented. The results from Ginga indicate that the region around the centrally dominant galaxy NGC 1275 is well described by a model incorporating emission from an isothermal, diffuse plasma of temperature ∼6.3 keV, metal abundance ∼0.4 solar, a cooling flow with a mass deposition rate ∼270 M ⊙ /Yr and photoelectric absorption from a galactic column density of 1.3 × 10 21 atom cm −2 . This value is also consistent with the EXOSAT observations. The metal abundance is constrained to within 5 per cent making this the most precise determination of the metallicity of a cluster to date

X-ray observations of the Seyfert 1 galaxy Markarian 464

Results of EXOSAT (0.05-10 keV) and hard X-ray (25-45 keV) balloon observations (XG-81) of the Seyfert 1 galaxy Mrk 464 are presented. The spectrum observed with EXOSAT is well fitted by a power law with a photon spectral index 1.70 ± 0.15, in agreement with a previous measurement by HEAO 1 A-2. The absorption column density is found consistent with the galactic column density. Both the EXOSAT and the HEAO 1 upper limit are in disagreement with the very high column density observed by Ariel 5. The XG-81 experiment detected a bright hard X-ray source in a field of view centered on Mrk 464

The EXOSAT high Galactic latitude survey

We have performed a survey of ~570 square degrees of high galactic latitude sky using a large number of EXOSAT X-ray images. 130 serendipitous sources were detected and ~ 60% of them have been identified with catalogued objects. The large majority of the remaining sources have faint optical counterparts on POSS or ESO plates and are expected to be extragalactic. The comparison of our results with those of the Einstein Medium Sensitivity Survey and an analysis of the correlation between the spatial distribution of EXOSAT serendipitous sources and the amount of galactic Hydrogen column density indicate that the average spectral index of extragalactic X-ray sources is steeper than the canonical AGN slope.

The albedo and scattering phase function of interstellar dust and the diffuse background at far-ultraviolet wavelengths.

We have determined the scattering parameters of dust in the interstellar medium at far-ultraviolet (FUV) wavelengths (1415-1835 angstroms). Our results are based on spectra of the diffuse background taken with the Berkeley UVX spectrometer. The unique design of this instrument makes possible for the first time accurate determination of the background both at high Galactic latitude, where the signal is intrinsically faint, and at low Galactic latitude, where direct starlight has heretofore compromised measurements of the diffuse emission. Because the data are spectroscopic, the continuum can be distinguished from the atomic and molecular transition features which also contribute to the background. We find the continuum intensity to be well correlated with the Galactic neutral hydrogen column density until saturation at about 1200 photons cm-2 s-1 sr-1 angstrom-1 is reached where tau FUV approximately 1. Our measurement of the intensity where tau FUV > or = 1 is crucial to the determination of the scattering properties of the grains. We interpret the data with a detailed radiative transfer model and conclude that the FUV albedo of the grains is low (<25%) and that the grains scatter fairly isotropically. We evaluate models of dust composition and grain-size distribution and compare their predictions with these new results. We present evidence that, as the Galactic neutral hydrogen column density approaches zero, the FUV continuum background arises primarily from scattering by dust, which implies that dust may be present in virtually all view directions. A non-dust-scattering continuum component has also been identified, with an intensity (external to the foreground Galactic dust) of about 115 photons cm-2 s-1 angstrom-1. With about half this intensity accounted for by two-photon emission from Galactic ionized gas, we identify roughly 50 photons cm-2 s-1 sr-1 angstrom-1 as a true extragalactic component.

Accurate galactic N(H) values towards quasars and AGN

Integrated Galactic 21-cm column densities toward about 174 quasars and AGN are presented. The data are corrected for stray radiation, using the technique of Lockman et al. (1986). Because of the 21-arcmin beam size of the 140-ft telescope used in the study, the uncertainty in N(H) due to angular variations in the H I of the Galaxy at high latitudes is minimized. The column densities are accurate to about 1 X 10 to the 19th atoms/sq cm, or 5 percent, whichever is larger. Errors above N(H) of about 4 X 10 to the 20th atoms/sq cm are dominated by opacity uncertainties.

Einstein spectra of quasars

The results of the initial stage of the CfA survey of Quasar Energy Distributions (QEDs) are reviewed. Einstein Imaging Proportional Counter (IPC) spectra of 33 quasars have been studied by fitting a single power law slope and absorption by an equivalent column density of neutral hydrodgen, N H . A wide range of energy index, α E , is seen and α E increases as the radio loudness of a quasar decreases. Comparison with the higher energy HEAO-A2 data leads us to a two-component model for th x-ray spectrum. The x-ray column density is systematically lower than the 21 cm measured Galactic column density along the same line of sight. This discrepancy is not present in a comparison sample of Bl Lac objects and so the cause must be intrinsic to the quasar. A third component, an ultra-soft excess (<0.28keV) above a single power law in the quasar spectra, provides a plausible explanation. This excess could be the high energy tail of the blue bump in the optical and ultra-violet (UV).

The X-ray spectrum of Markarian 509 observed by EXOSAT

view Abstract Citations (27) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The X-Ray Spectrum of Markarian 509 Observed by EXOSAT Morini, M. ; Lipani, N. A. ; Molteni, D. Abstract Mrk 509 was observed with Exosat at three different epochs during October and November 1983. Variability of about 30 percent was apparent both in the medium-energy (1-10 keV) and in the low-energy (less than 2 kev) X-ray bands between the different observations, on a time scale of 10 days. No correlation between the two energy bands was observed. The 1-10-keV spectrum of the source is best fitted by a power law with energy index 0.8. In addition, a fluorescence iron line is required to fit the data obtained on Nov. 3, 1983. The best-fit energy of the line is 6.31 + or - 0.21 keV (source frame) and the equivalent width 316 + or - 100 eV. No low-energy interstellar absorption is observed in the medium-energy spectra. When the low-energy photometric data are included in the spectral analysis, the single-power-law model requires an absorption density considerably smaller than the Galactic column density in the direction of the source: this can be fitted only through a variable soft X-ray component (VSXC). If a thermal spectrum is assumed for VSXC, a temperature of about 70 eV can be inferred from the data. The VSXC and the presence of the iron fluorescence line, have interesting implications on the source model: a limit on the size of the soft X-ray emission region of 10 to the 16th cm can be derived, and the fluorescent material must be hot, with a temperature in the range 50-80 million K, and have a flat spatial distribution. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/165262 Bibcode: 1987ApJ...317..145M Keywords: Satellite Observation; Seyfert Galaxies; X Ray Spectra; Emission Spectra; Exosat Satellite; Spectrum Analysis; Astrophysics; GALAXIES: INDIVIDUAL NAME: MARKARIAN 509; GALAXIES: SEYFERT; X-RAYS: SPECTRA full text sources ADS | data products SIMBAD (1) NED (1)

The EXOSAT High Galactic Latitude Survey

We have performed a survey of ∼570 square degrees of high galactic latitude sky using a large number of EXOSAT X-ray images. 130 serendipitous sources were detected and ∼60% of them have been identified with catalogued objects. The large majority of the remaining sources have faint optical counterparts on POSS or ESO plates and are expected to be extragalactic. The comparison of our results with those of the Einstein Medium Sensitivity Survey and an analysis of the correlation between the spatial distribution of EXOSAT serendipitous sources and the amount of galactic Hydrogen column density indicate that the average spectral index of extragalactic X-ray sources is steeper than the canonical AGN slope.