2004/01/14 by S. Vaughan, R. Edelson, Rick Edelson +1
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Galaxy #Luminosity #Neutron star #Physics #ROSAT #Sky #Spectral line #X-ray #X-ray transient #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2004.07615.x
published as Mon.Not.Roy.Astron.Soc. 349 (2004) L1 · 5 pages. 3 figures. Accepted for publication in MNRAS
arxiv created 2004/01/14 · openalex publication_date 2004/03/09 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We report on exploratory Chandra observations of five galactic nuclei that were found to be X-ray bright during the ROSAT All-Sky Survey (with LX≳ 1043 erg s−1) but subsequently exhibited a dramatic decline in X-ray luminosity. Very little is known about the post-outburst X-ray properties of these enigmatic sources. In all five cases Chandra detects an X-ray source positionally coincident with the nucleus of the host galaxy. The spectrum of the brightest source (IC 3599) appears consistent with a steep power law (Γ∼ 3.6). The other sources have too few counts to extract individual, well-determined spectra, but their X-ray spectra appear flatter (Γ∼ 2) on average. The Chandra fluxes are ∼102–103 fainter than was observed during the outburst (up to 12 yr previously). That all post-outburst X-ray observations have seen a similarly low X-ray luminosities is consistent with these sources having ‘switched’ to a persistent low-luminosity state. Unfortunately the relative dearth of long-term monitoring and other data mean that the physical mechanism responsible for this spectacular behaviour is still highly unconstrained.