* Astronomy

Members Login
    Remember Me  
Post Info TOPIC: NGC821


Posts: 131433

Title: A deep Chandra look at the low L_B elliptical NGC821: not only wind and X-ray binaries
Authors: S. Pellegrini (1), A. Baldi (2), D.W. Kim (2), G. Fabbiano (2), R. Soria (2,3), A. Siemiginowska (2), M. Elvis (2) ((1) Astronomy Dept., Bologna University, Italy; (2) Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA); (3) Mullard Space Science Laboratory, University College London, UK)

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 centre 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 centre 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.

Read more (582kb, PDF)

Page 1 of 1  sorted by
Quick Reply

Please log in to post quick replies.

Create your own FREE Forum
Report Abuse
Powered by ActiveBoard