XMM/HST monitoring of the ultra soft Narrow Line Seyfert 1 RX J1355.2+5612

Ultra soft Narrow Line Seyfert 1 are characterized by a large spectralvariability, a very steep Xray primary continuum (> 2.5) and a strong softexcess. This remarkable spectral shape questions the origin of their broadbandUVXray continuum compared to standard Seyfert galaxies. We propose to performa monitoring composed of 5 x 26 ks XMM observations (total: 130 ks), spaced by23 days and coordinated with HST, to probe the FUV, of RX J1355.2+5612. Theproposed monitoring will allow us to 1) disentangle the different spectralcomponents present from the UV/FUV to Xray energy range and 2) investigate thenature of the soft Xray excess and discriminate between the theoretical modelsthat have been heavily discussed in the past decade truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]