2008/09/24 by Dirk Grupe, Karen M. Leighly, Stefanie Komossa
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Distribution (mathematics) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Photon #ROSAT #Spectral energy distribution #Spectral power distribution #Swift #Transient (computer programming) #astro-ph
paper · pdf · doi:10.1088/0004-6256/136/6/2343
Accepted for publication in the Astronomical Journal, scheduled for December 2008, 8 pages, 3 figures, 3 tables
arxiv created 2008/09/24 · openalex publication_date 2008/11/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report on the first detection of hard X-ray photons ( E > 2.5 keV) in the X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007 which was the active galactic nucleus (AGN) with the softest X-ray spectrum during the ROSAT All-Sky Survey. The AGN is clearly detected at a level of about 2 × 10 −17 W m −2 in the observed 0.3–10.0 keV band by Swift in a 50 ks observation in 2007 September. For the first time since the ROSAT All-Sky Survey observation in 1990 it was possible to derive an X-ray photon distribution by adding together all Swift observations that have been performed so far (85.5 ks in total). This photon distribution is consistent with an X-ray spectrum of an AGN with a partial covering absorber with a column density in the order of ∼1 × 10 23 cm −2 and a covering fraction of about 90%. A comparison with the 2002 Chandra data suggests that WPVS 007 has become brighter by a factor of about 4. The Swift data also suggest that the absorber which is causing the current low state may have started to disappear. This disappearance is indicated by a significant change in the hardness ratio from a very soft X-ray state during the 2005 October to 2007 January observations to a rather hard X-ray state in the 2007 September observations. In the UV, WPVS 007 seems to become fainter by up to 0.5 mag over the last two years. The optical to X-ray spectral slope derived from the spectral energy distribution is α ox = 2.5 which classifies WPVS 007 as an X-ray weak AGN. After correcting for reddening and X-ray absorption, α ox becomes 1.9 and the luminosity in the Big-Blue-Bump is log L BBB = 37.7 [W], which translates into an Eddington ratio L / L Edd ≈ 1.