Engineering topics

Fabbiano, G.

Publications and source records attributed to Fabbiano, G..

At least 55 records · Page 3

NASA NTRS1988

X-ray spectra and large-scale features of two starburst galaxies - NGC 253 and M82

The results of Einstein Observatory IPC X-ray observations of the well-known nearby starburst galaxies NGC 253 and M82 are presented. The major axis X-ray surface brightness profile of NGC 253 is steeper than the optical profile, but follows the radio continuum distribution closely. Extended X-ray emission with no optical or radio counterpart is found on the northern side of this galaxy. It is suggested that this emission may be due to gaseous clouds ejected from the starburst nucleus. The X-ray halo of M82 extends as far as 9 arcmin away from the nucleus along the minor axis. The radial distribution of the X-ray surface brightness of this halo is steep and suggests a density distribution proportional to 1/r-squared, typical of free-flowing winds. The spectral properties of the nuclear regions are different from those of the surrounding emission. They are fitted with large intrinsic absorption columns and possibly lower emission temperatures.

Fabbiano, G.↗

NASA NTRS1988

Morphology and spectral characteristics of the X-ray emission of M33

A previous analysis of the X-ray data on M33 has been extended to include a detailed study of the morpholgoy and spectral characteristics of the X-ray emission, and the results are reported. A low surface brightness, extended emission in the plane of the galaxy is detected. The X-ray luminosity of this component, about 10 to the 38th egs/s, is comparable to the total luminosity of the bright sources observed in the same region. Its radial distribution is similar to that of the blue light. The spectrum of the extended emission shows two distinct components: a hard one, with a temperature above 3 keV and a soft one with a temperature below 1 keV. The X-ray spectrum of the nuclear source, which is inconsistent with any of the known spectra of X-ray binary sources, can be fitted with either a low-temperature thermal emission or a steep power law model.

Trinchieri, G.↗

NASA NTRS1988

The X-ray emission of M81 and its nucleus

X-ray observations of M81 made with the Einstein satellite are analyzed, and the results are reported. Eight bright sources other than the nucleus were detected, with luminosities in excess of about 2 x 10 to the 38th ergs/s. These are probably young, massive, accreting binary systems. A comparison of M81 with the morphologically similar galaxy M31 shows that the former is overluminous in both the radio continuum and the X-ray emission and to a lesser extent the far-infared emission, relative to the optical luminosity. This points to a difference in the star-formation histories of the two galaxies. The individual X-ray sources detected in M81 are all more luminous than the most luminous sources of M31. The nuclear source in M81 has a very soft and absorbed X-ray spectrum which cannot be explained by either inverse Compton radiation of the compact nuclear radio source or by an extension of the radio synchrotron emission.

Fabbiano, G.↗

NASA NTRS1988

A five-band study of spiral galaxies - X-ray, optical, near- and far-infrared, and radio continuum correlations

A statistical analysis is given of the relationships between global emission properties of spiral galaxies, including the radio continuum, far-infared, near-infrared H-band, optical (B), and X-ray emission. Different properties are observed in early-type and in late-type spiral galaxies, which can be ascribed to the presence of prominent bulges in the former. In late-type spirals, the statistical properties of the emission at different wavelengths are consistent with a common disk/arm origin. The power-law exponents of the correlations are consistent with a steeper IMF in low-luminosity galaxies and with the presence of an obscured starburst component in high-luminosity galaxies. The strongest correlation of the radio continuum luminosity with any other variable is with the far-infrared, suggesting that the radio emission is disjoint from the older low-mass stellar component.

Fabbiano, G.↗

NASA NTRS1987

The X-ray spectral properties of the bulge of M31

The results of a spectral analysis of the Einstein observations of the bulge of M31 are reported. The data can be fitted with a hard thermal spectrum with characteristic temperature kT of about 6-13 keV (at 90 percent confidence). No intrinsic absorption above the galactic value of N(H) is required. These results are in agreement with the presence in the bulge of M31 of a population of low-mass binary sources similar to those of the Milky Way.

Fabbiano, G.↗

NASA NTRS1987

X-ray observations of spiral galaxies. II - Images and spectral parameters of 13 galaxies

The results of a spatial and spectral analysis of a sample of spiral galaxies observed in X-rays with the Einstein satellite indicate that the X-ray emission is generally extended and complex. In some cases, discrete, very bright X-ray sources are detected, some of these coincident with the nuclear regions. The spectral fit of the IPC data to a thermal bremsstrahlung spectrum with a low-energy absorption cutoff shows that the average spectrum could be rather hard with kT greater than 2 keV, and with low-energy cutoff consistent with line-of-sight absorption. Results on NGC 4631, NGC 6946, and the nuclei of IC 342 and NGC 1313 are discussed and compared with previous observations in different energy ranges.

Fabbiano, G.↗

NASA NTRS1987

The continuum of type 1 Seyfert galaxies. I - A single form modified by the effects of dust

Broad-band measurements from 1 to 20 microns of 26 emission-line active galactic nuclei (AGNs), mainly Seyfert 1 galaxies, have been made. These data have been combined with previous optical and infrared photometry and IRAS 12, 25, 60 and 100 micron fluxes, giving a total sample of 37 AGNs, all of which have hard X-ray measurements. The sample includes all the emission-line AGNs identified in the Piccinotti et al. (1982) survey. When corrected for stellar contributions in the near-infrared, the continuum energy distributions can be classified observationally into three types: (1) bare, minimally reddened AGNs; (2) reddened AGNs; and (3) AGNs for which the far-infrared emission is contaminated by the host galaxy. These classifications reflect a range of luminosities and different environments rather than intrinsic differences in the primary continuum of the AGNs. The data are consistent with a single underlying form of active galaxy continuum modified by the presence of dust and of the host galaxy.

Ward, Martin↗

NASA NTRS1987

X-ray spectra of PG quasars. II - The X-ray-ultraviolet excess of PG 1211 + 143

Observations of the quasar PG 1211 + 143 are presented and its continuum is modelled in terms of an accretion disk and an underlying power law. The X-ray spectrum in the Einstein imaging proportional counter band is well described by a power law with the very steep spectral index 2.2 + or - 0.4. The overall continuum spectral energy distribution can be described as a power law with alpha roughly 1.2 from the infrared to about 1 keV, with the optical, ultraviolet, and soft X-rays forming a large excess above this power law. If the soft X-ray excess is attributed to emission from a physically thin, optically thick accretion disk, then the implied accretion rate is super-Eddington, from which it is concluded that the application of this simple model is not valid. The observed broad-line ratios in PG 1211 + 143 imply broad-line cloud densities that are somewhat higher than those usually derived for quasars.

Bechtold, Jill↗

NASA NTRS1987

A statistical analysis of the Einstein normal galaxy sample. III - Radio and X-ray properties of elliptical and S0 galaxies

Radioastronomy, optical and X-ray data were used to probe the cause of high X-ray luminosities of 28 radio-quiet elliptical galaxies (RQE) and S0 galaxies previously scanned by the Einstein Observatory. Comparisons were made with similar data on double-lobed 3CR galaxies. Radio luminosities were highly correlated with the X-ray luminosities, agreeing with models of radio nuclear sources in early-type galaxies as accreting compact objects. Additionally, 3CR galaxies seemed to be large-scale versions of normal RQE. The significance of interstellar medium/intracluster medium interactions for high correlations between the core and total radio power from X-ray emitting galaxies is discussed.

Fabbiano, G.↗

NASA NTRS1986

The X-ray surface brightness distribution and spectral properties of six early-type galaxies

Detailed analysis is presented of the Einstein X-ray observations of six early-type galaxies. The results show that effective cooling is probably present in these systems, at least in the innermost regions. Interaction with the surrounding medium has a major effect on the X-ray surface brightness distribution at large radii, at least for galaxies in clusters. The data do not warrant the general assumptions of isothermality and gravitational hydrostatic equilibrium at large radii. Comparison of the X-ray surface brightness profiles with model predictions indicate that 1/r-squared halos with masses of the order of 10 times the stellar masses are required to match the data. The physical model of White and Chevalier (1984) for steady cooling flows in a King law potential with no heavy halo gives a surface brightness distribution that resembles the data if supernovae heating is present.

Trinchieri, G.↗

NASA NTRS1986

The X-ray properties of normal galaxies

X-ray observations with the Einstein satellite have shown that normal galaxies of all morphological types are spatially extended sources of X-ray emission with luminosities in the range of L(x) of about 10 to the 39th to 10 to the 41st erg/s. Although this is only a small fraction of the total energy output of a normal galaxy, X-ray observations are uniquely suited to study phenomena that are otherwise elusive. In X-rays one can study directly the end products of stellar evolution (SNRs and compact remnants). X-ray observations have led to the discovery of gaseous outflows linked to starburst nuclear activity in spiral galaxies and to the detection of a hot interstellar medium in early-type galaxies. Through X-ray observations it is possible to set constraints on structural galaxy parameters, such as the mass of elliptical galaxies, and perhaps get new insight on the origin of cosmic rays and the properties of the magnetic fields of spiral galaxies.

Fabbiano, G.↗

NASA NTRS1986

The highly obscured nucleus of 3C 219

The detection of a strong, and possibly broad, Paschen-alpha line from the narrow-line radio galaxy 3C 219 is reported. The detected flux is larger than predicted from the H-alpha line and the case B recombination. This implies the presence of a highly reddened line-emitting region in the nucleus.

Fabbiano, G.↗

NASA NTRS1985

An X-ray study of M51 (NGC 5194) and its companion (NGC 5195)

The galaxy M51 and its companion NGC 5195 were observed with the Einstein High-Resolution Imager. The X-ray observations led to the detection of both galaxies with (0.2-4.0 keV) X-ray luminosities of 3.0 x 10 to the 40th ergs/s and 2.1 x 10 to the 39th ergs/s respectively. M51 and its companion are compared to other spiral and irregular galaxies observed in X-rays, and the various components of the X-ray emission of M51 (i.e., nucleus, point sources, and unresolved extended emission) are discussed.

Palumbo, G. G. C.↗

NASA NTRS1985

A statistical analysis of the Einstein normal galaxy sample. I - Spiral and irregular galaxies

The results of a statistical analysis of 48 spiral and irregular galaxies observed with the Einstein Observatory are reported. It is found that the X-ray luminosity is not directly correlated with the mass of the galaxies, but is strongly correlated with the blue luminosity. This suggests that most X-ray sources, including low-mass binaries, are binary systems belonging to both old disk and young arm Population I components. A real bulge population of X-ray sources exists that can contribute significantly to the X-ray luminosity of early-type spirals. The X-ray emission from a sample of 29 relatively isolated, normal elliptical and S0 galaxies is also studied, and the results are compared to those for the above sample to investigate the origin of the X-ray emission in early-type galaxies and the possible emission mechanisms. The influence of a powerful radio source and the onset of nuclear activity are also examined.

Fabbiano, G.↗

NASA NTRS1985

The X-ray properties of normal galaxies. What do we know and what can we learn with the next generation of X-ray telescopes?

Einstein Observatory results are used to assess the possibilities of spaceborne X-ray astronomy projects such as XMM (ESA) and AXAF (NASA). Einstein observations show that normal galaxies of all morphological types are spatially extended sources of X-ray emission with 0.5 to 3.0 keV X-ray luminosities of 10 to the 39th to 41st power erg/sec. X-ray telescopes can study the end products of stellar evolution in galaxies of different morphological types. Phenomena linked to starburst nuclear activity can best be detected and studied in X-ray. Hot coronae or a hot phase of the interstellar medium can only be studied through their X-ray emission. It is shown that high spatial resolution is essential for studying normal galaxies and identifying different emission regions. Good spectral sensitivity and spectral imaging capability are essential for gaining a deeper understanding of the phenomena at work.

Fabbiano, G.↗

NASA NTRS1985

The gaseous environments of double radio galaxies

A detailed investigation is made of the X-ray emission from five 3CR double radio galaxies, and upper limits are set to the X-ray emissivity of the regions around the radio lobes. These limits, when combined with the expected behavior of hot gas in and around the lobes, show that most of the radio-emitting plasma observed is unlikely to be maintained in static pressure-balance with an external medium. The plasma must expand, and the luminosities of double radio galaxies may therefore decrease with time for most of their lifetimes. A lower limit on the magnetic field strength in the lobes of one-tenth the equipartition value is also derived.

Miller, L.↗

NASA NTRS1985

Observations from 1 to 20 microns of low-luminosity active galaxies

The 1-20 micron photometry of Liners (Low Ionization Nuclear Emission-line Regions), star burst nuclei, and high-excitation (mostly Seyfert 2) nuclei are presented and discussed. Liners have strong, flattish 10-20 micron excesses but are dominated by a stellar population through 1-5 micron. By contrast, most type 2 Seyfert galaxies and all star-burst nuclei have flux distributions that are flat through 1-5 microns, and steeply rising through 10-20 microns. The 1-5 micron flux distributions of type 2 Seyfert galaxies and starburst nuclei can be explained by mixtures of stellar emission, recombination radiation, and hot dust, although a nonthermal component is likely in a few objects. One Liner, NGC 3079, was found to be extended to 10 microns. A map which shows the 10-micron and optical maxima to differ by 6 arcsec is presented.

Lawrence, A.↗

NASA NTRS1985

An X-ray study of M51 (NGC 5194) and its companion (NGC 5195)

Observations of NGC 5194/95 with the Einstein HRI show a very strong nuclear X-ray source, surrounded by a diffuse flux, three point sources, and the companion. The diffuse flux, which correlates well with the radio continuum, is likely to originate from the disk population with an age of approximately 2.1 billion yrs. The large luminosity from the nuclear source, together with optical and radio observations, shows that it belongs to the low luminosity active nuclei, thus extending this class to luminosities of less than about 10 to the 40th erg/s.

Palumbo, G. G. C.↗