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Astron. Astrophys. 319, 74-82 (1997)

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The ultraviolet to X-ray spectrum of the Seyfert 1 galaxy E 1615+061: accretion disk and reflection models

L. Piro 1, M. Balucinska-Church 2, H. Fink 3, F. Fiore 4, M. Matsuoka 5, G.C. Perola 6 and P. Soffitta 1

1 Istituto Astrofisica Spaziale, C.N.R., Via E. Fermi 21, C.P. 67, I-00044 Frascati (Rm), Italy
2 School of Physics and Space Research, University of Birmingham, B15 2TT, UK
3 Max Planck Institute for Extraterrestrial Physics, Garching, Germany
4 Osservatorio Astronomico di Roma, Via dell'Osservatorio, I-00044 Monteporzio Catone, Italy
5 RIKEN, The Institute of Physical and Chemical Research, Wako-shi 351-01, Japan
6 Dipartimento di Fisica, Universita' di Roma 3, Via della Vasca Navale 84, I-00146 Roma, Italy

Received 14 March 1996 / Accepted 22 July 1996


The Seyfert 1 galaxy E 1615+061 is a candidate for the strongest variability in soft X-rays, changing from a very steep high state ([FORMULA]), as implied by HEAO1 observations performed in 1977, to a two orders of magnitude dimmer state with a flatter spectrum ([FORMULA]), as observed by EXOSAT in 1985. In this paper we present the results of a campaign of (quasi)-simultaneous observations with IUE, ROSAT and GINGA in 1990-1992. We found that the X-ray luminosity was about 6 times larger than observed by EXOSAT, though the object did not attain the level observed by HEAO-1. The UV to X-ray spectrum observed in our campaign shows the presence of a UV bump and a soft X-ray excess. These components are formally fitted by a standard thin accretion disk model. We find however that this model is not self-consistent, due to the high level of ionization expected for the high value of accretion rate, which leads to an over-production of soft X-rays by reflection. A self-consistent explanation is found in the low accretion rate regime. In this case reflection by mildly ionized regions of the disk produces the soft excess and the direct emission from the disk accounts for the UV emission but does not extend to the soft X-ray region. Some evidence for a line at around 0.6 keV, attributed to OVII/OVIII, supports the presence of an ionized reflector. The spectra observed by EXOSAT and HEAO1 can be successfully explained by this model in the regimes of very low and high accretion rates.

Key words: galaxies: individual: E 1615+061 – galaxies: nuclei – galaxies: Seyfert – ultraviolet: galaxies – X-rays: galaxies

Send offprint requests to: L. Piro: piro@alpha1.ias.fra.cnr.it

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998