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A deep Chandra look at the low L_B elliptical NGC821: not only wind and X-ray binaries | | S. Pellegrini
; A. Baldi
; D.W. Kim
; G. Fabbiano
; R. Soria
; A. Siemiginowska
; M. Elvis
; | | Date: |
23 Jan 2007 | | Abstract: | The nearby, low L_B elliptical galaxy NGC821, known to host a central massive black hole but inactive at all wavelengths, has been observed with deep Chandra pointings, for a total exposure of 230 ksec, in order to search for nuclear emission and gas available for accretion. Within its optical image, 41 X-ray sources are detected, with spectral properties typical of low mass X-ray binaries (LMXBs); their X-ray luminosity function (XLF) was derived down to a 0.3-8 keV luminosity of 3X10^{37} erg/s. At the position of the galactic center a source of L(0.3-8 keV)=6X10^{38} erg/s is detected for the first time. This source is surrounded by three other sources with a spectral shape typical of LMXBs and luminosities on the brightest end of the XLF. Only one is consistent with being pointlike, and one of them resembles a jet-like feature. Diffuse emission is detected out to a radius of ~30" and comes mostly from unresolved LMXBs, with a possible minor contribution from other types of stellar sources. Hydrodynamical simulations specific for NGC821 show that the hot gas is driven out of the galaxy in a wind sustained by type Ia supernovae, but also that it is accreting towards the center from within a very small inner region. A companion paper (Pellegrini et al. 2006) presents further observational results obtained with Spitzer and the VLA, and discusses possible accretion modalities for this central massive black hole. | | Source: | arXiv, astro-ph/0701639 | | Services: | Forum | Review | PDF | Favorites | |
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