XMM-Newton observations of the Seyfert 1 galaxy Mrk 335

We report on an XMM-Newton observation of the Seyfert 1 galaxy Mrk 335 performed in December 2000. The power law component of its spectrum above 2 keV has a photon index Gamma =2.3 much steeper than that of a ``normal'' Seyfert 1 galaxy. A broad spectral feature is observed around 6.0 keV (+/-1 keV) that can be fitted by a relativistic emission profile or by an edge. A soft excess above the power law rises steeply below 2 keV and represents more than 30% of the intrinsic source luminosity in the 0.3-2 keV band. Large luminosity (Delta L > 5x 10⁴² erg s^-1) variations on time scales of a few ksec support the view that gravitational energy conversion linked with the presence of a supermassive object is likely responsible for the X-ray emission from Mrk 335 nucleus. The relativistic line profile points to a scenario where the iron K emission arises from highly ionized material in the innermost region of an accretion disk surrounding a rotating black hole. The soft excess emission partly results from reprocessing onto the highly ionized inner region of the disk of a power law continuum produced by inverse Compton scattering of UV photons within a corona above the disk. Thermal emission produced by the viscous heating of the disk itself could also contribute to the soft excess emission in Mrk 335. We argue that, within the innermost region of the disk, the dynamics of accretion could become similar to spherical accretion and advection-dominated with a radiation efficiency as low as 0.25%. A rate of accretion constrained to 13% of the Eddington limit onto a central 10⁷ M_sun object would then translate into 1.6 x 10^-2 M_sun yr^-1. We further conjecture that Mrk 335 might be in a transition between a normal Seyfert 1 state and an ultra-soft NLS1 state where the soft-excess emission would be fully dominated by the intrinsic emission from the accreting material.