An Exceptional Change in the X-Ray Flux and Spectrum of the Seyfert 1 Galaxy E1615+061

Abstract

The Seyfert 1 galaxy E1615 + 061 was found with the HEAO 1 A-2 experiment to possess a very soft X-ray spectrum, with an energy spectral index α >~ 2, much greater than typical (α ~ 0.6) for objects of the same class. The two EXOSAT observations described in this Letter show that in 1985 July this object was fainter than the HEAO 1 measurement by more than two orders of magnitude in the 0.1-0.3 keV band and, with a change {DELTA}α >~ 2, had recovered the spectral shape typical of its class. This unique spectral behavior could represent the extreme case of a highly variable soft X-ray excess (such as the one found by EXOSAT in several other Seyfert 1 galaxies) which at the highest level of intensity extends and dominates the emission well beyond 1 keV. If this excess is described with a thermal bremsstrahlung, a change in kT by at least a factor of 2 is needed to explain the observed spectral variation.