Wednesday, July 31, 2013

1307.7713 (Dirk Grupe et al.)

Strong UV and X-ray variability of the Narrow Line Seyfert 1 Galaxy WPVS 007 -- on the nature of the X-ray low state    [PDF]

Dirk Grupe, S. Komossa, Julia Scharwaechter, Matthias Dietrich, Karen M. Leighly, Adrian Lucy, Brad N. Barlow
We report on multi-wavelength observations of the X-ray transient Narrow Line Seyfert 1 (NLS1) galaxy WPVS 007. The galaxy was monitored with Swift between October 2005 and July 2013, after it had undergone a dramatic drop in its X-ray flux earlier. For the first time, we are able to repeatedly detect this NLS1 in X-rays again. This increased number of detections in the last couple of years may suggest that the strong absorber that has been found in this AGN is starting to become leaky, and may eventually disappear. The X-ray spectra obtained for WPVS 007 are all consistent with a partial covering absorber model. A spectrum based on the data during the extreme low X-ray flux states shows that the absorption column density is of the order of 4 x 10^23 cm^-2 with a covering fraction of 95%. WPVS 007 also displays one of the strongest UV variabilities seen in Narrow Line Seyfert 1s. The UV continuum variability anti-correlates with the optical/UV slope alpha-UV which suggests that the variability primarily may be due to reddening. The UV variability time scales are consistent with moving dust `clouds' located beyond the dust sublimation radius of approximately 20 ld. We present for the first time near infrared JHK data of WPVS 007, which reveal a rich emission-line spectrum. Recent optical spectroscopy does not indicate significant variability in the broad and FeII emission lines, implying that the ionizing continuum seen by those gas clouds has not significantly changed over the last decades. All X-ray and UV observations are consistent with a scenario in which an evolving Broad Absorption Line (BAL) flow obscures the continuum emission. As such, WPVS 007 is an important target for our understanding of BAL flows in low-mass active galactic nuclei (AGN).
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