Open AccessChandra observations of five X‐ray transient galactic nuclei
Author(s) -
Vaughan S.,
Edelson R.,
Warwick R. S.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07615.x
Subject(s) - physics , rosat , astrophysics , luminosity , galaxy , active galactic nucleus , sky , spectral line , astronomy , x ray , x ray transient , neutron star , quantum mechanics
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 L X ≳ 10 43 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 ∼10 2 –10 3 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.