AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 34. Imaging, Spectra and Variability of X-ray Emission in AGN
Oral, Monday, May 31, 1999, 2:00-3:30pm, Waldorf

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[34.03] The Mysterious, Dust-Free, X-Ray Absorber in Arp 102B

J. P. Halpern (Columbia U.), M. Eracleous (Penn State U.)

The broad-line radio galaxy Arp~102B is the prototypical active galaxy with double-peaked optical emission lines. In the course of studying its ultraviolet spectrum obtained with the Hubble Space Telescope, we stumbled upon a system of narrow, slightly blueshifted, metastable Fe~II absorption lines, the same transitiions that are seen in some low-ionization BALQSOs. We have since found that 3C~332, another broad-line radio galaxy with double-peaked emission lines, also sports such Fe~II absorption lines; it is deadringer for Arp~102B. We have not been able to decide which is more mysterious, the presence of these metastable absorbers in two BLRGs, or their absence in the vast majority of AGNs. To investigate further we obtained an X-ray spectrum of Arp~102B with ASCA, which we present in this paper. The X-ray spectrum is described by a power-law model with a photon index of about 1.6, i.e., it is relatively flat compared to the spectra of other broad-line radio galaxies and Seyfert galaxies. There is no detectable Fe~K\alpha line with an upper limit of 85 eV, if the line is unresolved, or 160 eV if the FWHM is 40,000 km s-1. The most interesting feature of the X-ray spectrum of Arp 102B is a significant neutral hydrogen column density of (3±0.6) \times 1021~{\rm cm}-2, in agreement with what an earlier ROSAT PSPC spectrum suggested. This absorber must be mostly free of dust because it does not seem to affect the relative strengths of the broad o ptical and ultraviolet emission lines. It is quite possible that the same absorbing medium is also responsible for the Fe~II absorption lines found in the ultraviolet spectrum of Arp~102B. The absorber could well be a slow, mostly neutral accretion-disk wind, since such a wind offers a plausible explanation for the emission-line properties. This work was supported by NASA through grant NAG5-8369.

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