1 research outputs found
Compact X-ray Sources in Nearby Galaxy Nuclei
We have found compact, near-nuclear X-ray sources in 21 (54\%) of a complete
sample of 39 nearby face-on spiral and elliptical galaxies with available ROSAT
HRI data. ROSAT X-ray luminosities (0.2 2.4 keV) of these compact X-ray
sources are 1010 erg~s. The mean displacement
between the location of the compact X-ray source and the optical photometric
center of the galaxy is 390 pc. ASCA spectra of six of the 21 galaxies
show the presence of a hard component with relatively steep (
2.5) spectral slope. A multicolor disk blackbody plus power-law model fits the
data from the spiral galaxies well, suggesting that the X-ray objects in these
galaxies may be similar to a black hole candidate (BHC) in its soft (high)
state. ASCA data from the elliptical galaxies indicate that hot (kT
0.7 keV) gas dominates the emission. The fact that the spectral slope of the
spiral galaxy sources is steeper than in normal type 1 active galactic nuclei
(AGNs) and that relatively low absorbing columns (N 10
cm) were found to the power-law component indicates that these objects
are somehow geometrically and/or physically different from AGNs in normal
active galaxies. The X-ray sources in the spiral galaxies may be BHCs,
low-luminosity AGNs, or possibly X-ray luminous supernovae. We estimate the
black hole masses of the X-ray sources in the spiral galaxies (if they are BHCs
or AGNs) to be 1010 M. The X-ray sources in the
elliptical galaxies may be BHCs, AGNs or young X-ray supernova also.Comment: 4 pages, TeX, two postscript figures, to be published in proceedings
of 32nd COSPAR Session E1.2 (1998 July 15-17 Nagoya) "The AGN-Normal Galaxy
Connection