First detection of hard X-ray photons in the soft X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007: The X-ray photon distribution observed by Swift

Abstract

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 AGN with the softest X-ray spectrum during the ROSAT All-Sky Survey. The AGN is clearly detected at a level of about 2 x 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 x 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 alpha-ox=2.5 which classifies WPVS 007 as an X-ray weak AGN. After correcting for reddening and X-ray absorption, alpha-ox becomes 1.9 and the luminosity in the Big-Blue-Bump is log LBBB=37.7 [W], which translates into an Eddington ratio L/LEdd ~ 1.0.

Accepted for publication in the Astronomical Journal, scheduled for December 2008, 8 pages, 3 figures, 3 tables

References in corpus (8)

• XMM-Newton observations of the Narrow-Line Seyfert 1 galaxy Mrk 335 in an historical low X-ray flux state
• Discovery of the Narrow-Line Seyfert 1 galaxy Mkn 335 in an historical low X-ray flux state
• Can the soft excess in AGN originate from disc reflection?
• Swift observations of high-redshift radio-loud quasars
• X-ray spectral variability in PG1535+547: the changing-look of a 'soft X-ray weak' AGN
• An Update on the X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007: Swift observations of UV variability and persistence of X-ray faintness
• Swift detection of all previously undetected blazars in a micro-wave flux-limited sample of WMAP foreground sources
• The Discovery of Soft X-ray Loud Broad Absorption Line Quasars

Cited by in corpus (6)

• Emergence of a Broad-Absorption-Line Outflow in the Narrow-line Seyfert 1 Galaxy WPVS 007
• PHL 1092 as a transient extreme X-ray weak quasar
• Investigating the {Origin} of the Absorption-Line Variability in Narrow-Line Seyfert 1 Galaxy WPVS 007
• Is there a connection between Broad Absorption Line Quasars and Narrow Line Seyfert 1 galaxies?
• Submm-bright X-ray absorbed QSOs at z~2: insights into the co-evolution of AGN and star-formation
• On the Origin of the Dramatic Spectral Variability of WPVS 007