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
We report on the detection of UV variability and the persistence of X-ray faintness of the X-ray transient narrow-line Seyfert 1 galaxy WPVS 007 based on the first year of monitoring with Swift between 2005 October and 2007 January. WPVS 007 has been an unusual source. Although it was X-ray-bright in the ROSAT All-Sky Survey, it has been extremely faint in all following X-ray observations. Swift also finds this NLS1 to be X-ray-faint, not detected at a 3 σ upper limit of 2.6×10-17 W m-2 in the 0.3-10.0 keV band, confirming that the AGN is still in a low state. During the 2006 July and December observations with the Swift UV-Optical Telescope (UVOT) the AGN became fainter by about 0.2 mag in the UV filters and by about 0.1 mag in V, B, and U compared with the 2005 October to 2006 January and 2006 September to October observations, followed by a rebrightening in the 2007 January observation. This variability can be caused either by a change in the absorption column density, and therefore the reddening in the UV, or by flux variations of the central engine. We also noticed that the flux in the UVOT filters agrees with earlier measurements by the International Ultraviolet Explorer taken between 1993 and 1995, but spectra taken by the Hubble Space Telescope Faint Object Spectrograph show that WPVS 007 was fainter in the UV by a factor of at least 2 in 1996. The flat optical/UV spectrum suggests that some UV extinction is present in the spectrum, but that alone cannot at all account for the dramatic fading in the X-ray flux. Most likely we see a partially covering absorber in the X-ray. Alternatively, the current X-ray emission seen from WPVS 007 may also be the emission from the host galaxy.
The Astronomical Journal
- Pub Date:
- May 2007
- galaxies: active;
- galaxies: individual: WPVS 007;
- Accepted for publications in the Astronomical Journal, 14 pages, 5 figures, 4 tables