Chandra Observations of the Quiescent Nuclear Black Hole of NGC 821: Evidence of Nuclear Activity?

Details Chandra Observations of the Quiescent Nuclear Black Hole of NGC 821: Evidence of Nuclear Activity? Chandra Observations of the Quiescent Nuclear Black Hole of NGC 821: Evidence of Nuclear Activity?

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...616..730f&link_type=abstract

The Astrophysical Journal, Volume 616, Issue 2, pp. 730-737.

Physics

22

Black Hole Physics, Galaxies: Individual: Ngc Number: Ngc 821, Galaxies: Nuclei, X-Rays: Galaxies

Scientific paper

We report the results of the Chandra ACIS-S observations of the elliptical galaxy NGC 821, which harbors a supermassive nuclear black hole (3.5×107 Msolar) but does not show signs of active galactic nucleus activity. A small, 8.5" long (~1 kpc at the galaxy's distance of 23 Mpc), possibly S-shaped, jetlike feature centered on the nucleus is detected in the 38 ks ACIS-S integrated exposure of this region. The luminosity of this feature is LX~2.6×1039 ergs s-1 (0.3-10 keV), and its spectrum is hard (described by a power law of Γ=1.8+0.7-0.6 or by thermal emission with kT>2 keV). We discuss two possibilities for the origin of this feature: (1) a low-luminosity X-ray jet, or (2) a hot shocked gas. In either case, it is a clear indication of nuclear activity, detectable only in the X-ray band. Steady spherical accretion of the mass losses from the central stellar cusp within the accretion radius, when coupled with a high radiative efficiency, already provides a power source exceeding the observed radiative losses from the nuclear region. A third possibility, that this feature may arise from a fortuitous distribution of luminous X-ray binaries in NGC 821, is also discussed.

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