Simultaneous XMM-Newton and HST-COS observation of 1H 0419–577

II. Broadband spectral modeling of a variable Seyfert galaxy

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: L.di.Gesu@sron.nl
² Osservatorio Astronomico di Roma (INAF), via Frascati 33, 00040 Monteporzio Catone ( Roma), Italy
³ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT, UK

Received: 25 October 2013
Accepted: 20 January 2014

Abstract

In this paper, we present the longest exposed (97 ks) XMM-Newton EPIC-pn spectrum ever obtained for the Seyfert 1.5 galaxy1H 0419–577. With the aim of explaining the broadband emission of this source, we took advantage of the simultaneous coverage in the optical/UV that was provided in the present case by the XMM-Newton Optical Monitor and by a HST-COS observation. Archival FUSE flux measurements in the far-ultraviolet were also used for the present analysis. We successfully modeled the X-ray spectrum and the optical/UV fluxes data points using a Comptonization model. We found that a blackbody temperature of T ~ 56 eV accounts for the optical/UV emission originating in the accretion disk. This temperature serves as an input for the Comptonized components that model the X-ray continuum. Both a warm (T_wc ~ 0.7 keV, τ_wc ~ 7) and a hot corona (T_hc ~ 160 keV, τ_hc ~ 0.5) intervene to upscatter the disk photons to X-ray wavelengths. With the addition of a partially covering (C_v ~ 50%) cold absorber with a variable opacity ( N_H~ [10¹⁹−10²²] cm^-2), this model can also explain the historical spectral variability of this source, with the present dataset presenting the lowest one ( N_H~10¹⁹ cm^-2). We discuss a scenario where the variable absorber becomes less opaque in the highest flux states because it gets ionized in response to the variations of the X-ray continuum. The lower limit for the absorber density derived in this scenario is typical for the broad line region clouds. We infer that1H 0419–577may be viewed from an intermediate inclination angle i ≥ 54°, and, on this basis, we speculate that the X-ray obscuration may be associated with the innermost dust-free region of the obscuring torus. Finally, we critically compare this scenario with all the different models (e.g., disk reflection) that have been used in the past to explain the variability of this source.