Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...447..121w&link_type=abstract
Astrophysical Journal v.447, p.121
Astronomy and Astrophysics
Astronomy
30
Galaxies: Nuclei, Galaxies: Seyfert, X-Rays: Galaxies
Scientific paper
We have reanalyzed 40 spectra of 25 Seyfert and narrow emission line galaxies (NELGs) and one QSO, all of which were obtained during the pointed observations phase (1978 May-1979 January) of the HEAO 1 A-2 experiment. This investigation was prompted by Ginga results which indicate that Fe Kα lines are common X-ray spectral features of active galactic nuclei (AGNs) and that a high-energy "bump" associated with reprocessing of nuclear radiation may be common as well. The HEAO 1 data, which cover the 2-40 keV energy band, provide a large sample of AGNs with which to test the Ginga results. New analysis techniques are employed which consist of simultaneous fitting of data from both the medium-energy (2-20 keV) and high- energy (3-40 keV) detectors, as well as the subtracting of summed background spectra (up to 230,000 s of data) in order to improve the ratio of signal to noise. These improved techniques have resulted in the detection of Fe K features and/or spectral flattening above ˜5-10 keV in ˜75% of the HEAO 1 sample. This confirms the Ginga result that spectral complexity is common in the X-ray spectra of Seyfert galaxies.
We find that strong Fe K lines tend not to be associated with the presence of high-energy flattening, implying that Fe Kα emission is not entirely the result of fluorescence from accretion disks. Our spectral results typically agree with Ginga for overlapping sources for which we have adequate signal-to-noise ratios, although we find a significantly larger reflection component in IC 4329A, NGC 5506, and Mrk 509. For IC 4329A and NGC 5506, a time lag in the response of the reflection component to variability in the intrinsic source flux can explain the presence of more reflection, since the sources were fainter during the HEAO 1 epoch. A similar effect can explain the larger reflection component in Mrk 509, provided the continuum underwent a flux outburst before or during HEAO 1 epoch.
Arnaud A. A. K.
Mushotzky Richard F.
Weaver Kimberley A.
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