Joint ROSAT-Compton GRO observations of the X-ray bright Seyfert galaxy IC 4329A

• Published in: The Astrophysical journal Vol. 438; no. 2; p. 672
• Main Authors: Madejski, G. M., Zdziarski, A. A., Turner, T. J., Done, C., Mushotzky, R. F., Hartman, R. C., Gehrels, N., Connors, A., Fabian, A. C., Nandra, K.
• Format: Journal Article
• Language: English
• Published: Legacy CDMS 10.01.1995
• Subjects: Astrophysics
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/175111

We report a simultaneous ROSAT and Gamma Ray Observatory (GRO) observation of the X-ray-bright Seyfert galaxy IC 4329A. For the GRO Oriented Scintillation Spectrometer Experiment (OSSE) detector, we also present the sum of the data for this and earlier observations. The overall spectrum is very well described as a power law with an energy spectral index of approximately 1 absorbed at low energies plus a strong Compton reflection component, typical for Seyfert 1 galaxies. The low energy absorption can be well described by a sum of a neutral column density of approximately 3 x 10(exp 21)sq cm, most of which is associated with the edge-on galactic disk of IC 4329A, plus an edgelike feature at approximately 700 eV; this feature implies either complex absorption (due to additional ionized material, or due to a partial covering), or a soft excess. The data only weakly constrain the presence of a high-energy cutoff in the underlying power law; they are compatible with an exponential cutoff at any energy E(sub c) approximately greater than 100 keV. The relative steepness of the OSSE data, with the power-law energy index of 1.6 +/- 0.2, can be accounted for entirely by the contribution of the high-energy tail of the reflection component when E(sub c) approaches infinity. (We find that the definite cutoff at an energy E(sub c)approximately 130 keV suggested in the recently published analysis of the OSSE data for this subject is due to a data reduction error.) Including nonsimultaneous Ginga observations with 2 keV fluxes matching well that of ROSAT gives us likely broad-band X-ray/gamma-ray spectra of the object from approximately 0.1 keV up to several hundred keV. We also report the ROSAT spectrum of the companion object to the Seyfert galaxy, the elliptical galaxy IC 4329.