The Nature of Accreting Black Holes in Nearby Galaxy Nuclei

Abstract

We have found compact X-ray sources in the center of 21 (54%) 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 ~ 1e37 - 1e40 erg/s (with a mean of 3e39 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. The fact that compact nuclear sources were found in nearly all (five of six) galaxies with previous evidence for a black hole or an AGN indicates that at least some of the X-ray sources are accreting supermassive black holes. ASCA spectra of six of the 21 galaxies show the presence of a hard component with relatively steep (Gamma approx 2.5) spectral slope. A multicolor disk blackbody model fits the data from the spiral galaxies well, suggesting that the X-ray object in these galaxies may be similar to a Black Hole Candidate in its soft (high) state. ASCA data from the elliptical galaxies indicate that hot (kT approx 0.7 keV) gas dominates the emission. The fact that (for both spiral and elliptical galaxies) the spectral slope is steeper than in normal type 1 AGNs and that relatively low absorbing columns (N_H approx 1e21 /cm2) 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 and elliptical galaxies may be black hole X-ray binaries, low-luminosity AGNs, or possibly young X-ray luminous supernovae. Assuming the sources in the spiral galaxies are accreting black holes in their soft state, we estimate black hole masses ~ 1e2 - 1e4 solar masses.Comment: 47 pages AASTEX, 6 postscript figures, plus two landscape tables (postscript), to appear in ApJ, revised version has fewer (single-spaced) page

HMXB, ULX and star formation

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Spectral state transitions of the Ultraluminous X-ray Source IC 342 X-1

“…Their high luminosities suggest they are either intermediate mass black holes (IMBH) (Colbert & Mushotzky 1999;Makishima et al 2000;Kaaret et al 2001), that their emission is beamed (e.g. Poutanen et al 2007;King 2009), or that they are stellar-mass BHBs that are emitting at super-Eddington rates (e.g.…”

Microquasars: Open Questions and Future Perspectives

“…Ultraluminous X-ray compact sources have been identified in several nearby spiral galaxies (Colbert & Mushotzky, 1999;Makishima et al 2000) as well as in dwarf galaxies (Mirioni & Pakull, 2000). These enigmatic sources have luminosities in the range of L x = 10 38−40 erg s −1 , and it has been proposed by Colbert & Mushotzky (1999) that they are BHs of 10 2−4 M ⊙ . Makishima et al (2000) propose that some of these superluminous sources are BHs as the microquasars GRS 1915+105 and GRO J1655-40, with masses below ∼100 M ⊙ and high disk temperatures because rapid rotation gets the disk closer to the BH, hence hotter.…”