English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The Narrow-line Seyfert 1 galaxy (NLS1) IRAS 13224$-$3809 is known to exhibitsignificant X-ray spectral variation, a sharp spectral drop at $\sim$ 7 keV,strong soft excess emission, and a hint of iron L-edge feature, which is verysimilar to the NLS1 1H 0707$-$495. We have proposed the "Variable DoublePartial Covering (VDPC) model" to explain the energy spectra and spectralvariability of 1H 0707$-$495 (Mizumoto, Ebisawa and Sameshima 2014, PASJ, 66,122). In this model, the observed flux/spectral variations below 10 keV withina $\sim$day are primarily caused by change of the partial covering fraction ofpatchy clouds composed by double absorption layers in the line of sight. Inthis paper, we apply the VDPC model to IRAS 13224$-$3809. Consequently, we havefound that the VDPC model can explain the observed spectral variations of IRAS13224$-$3809 in the 0.5$-$10 keV band. In particular, we can explain theobserved Root Mean Square (RMS) spectra (energy dependence of the fractionalflux variation) in the entire 0.5$-$10 keV band. In addition to the well-knownsignificant drop in the iron K-band, we have found intriguing iron L-peaks inthe RMS spectra when the iron L-edge is particularly deep. This feature, whichis also found in 1H 0707$-$495, is naturally explained with the VDPC model,such that the RMS variations increase at the energies where optical depths ofthe partial absorbers are large. The absorbers have a larger optical depth atthe iron L-edge than in the adjacent energy bands, thus a characteristic ironL-peak appears. On the other hand, just below the iron K-edge, the opticaldepth is the lowest and the RMS spectrum has a broad dip.

Origin of the Characteristic X-ray Spectral Variations of IRAS 13224$-$3809