1998/09/08 by Hartmut Schulz, Stefanie Komossa, S. Komossa +5
Decision Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Scientific Measurement and Uncertainty Evaluation #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9809088
to appear in the proc. of "Highlights in X-ray Astronomy" (Garching, June 1998); B Aschenbach et al. (eds)
arxiv created 1998/09/08 · openalex publication_date 1998/09/08 · arxiv updated 2009/12/01 · openalex created_date 2025/10/24 · openalex updated_date 2026/07/28
We briefly review and extend our discussion of the ROSAT detection of the extraordinarily luminous (>1042 erg/s) partly extended (> 30 kpc diameter) X-ray emission from the double-nucleus ultraluminous infrared galaxy NGC 6240. The ROSAT spectrum can be well fit by emission from two components in roughly equal proportions: a thermal optically thin plasma with kT ∼ 0.6 keV and a hard component that can be represented by a canonical AGN powerlaw. Source counts appear to have dropped by 30% within a year. Altogether, these findings can be well explained by a contribution of radiation from an AGN essentially hidden at other wavelengths. Fits of ASCA spectra, conducted by various groups, corroborate this result, revealing a high-equivalent width FeK blend which again is straightforwardly interpreted by scattered AGN light. If radiating at the Eddington limit, the central black hole mass does not exceed 107 Msun. We discuss implications for the formation of this AGN. However, the luminosity in the remaining extended thermal component is still at the limits of a pure starburst-wind-induced source. We suggest that the deeply buried starburst has switched to a partially dormant phase so that heating of the outflow is diminished and a cooling flow could have been established. This flow may account for the extended shock heating traced by LINER-like emission line ratios and the extremely luminous H2 emission from the central region of this galaxy. Next-generation X-ray telescopes will be able to test this proposal.