Recent X-Ray Observations of Seyferts and Emission-Line Galaxies

Abstract

It has been just a few years since Type 1 Seyferts were established as a class of X-ray sources with luminosities in the range 1042 - 1045 ergs s-1 by Elvis et al. (1978) using data from the sky survey instrument on Ariel V, and by Tananbaum et al. (1978) using data from UHURU.The average error-box sizes for X-ray sources identified with Type 1 Seyferts in the 2A catalog (Cooke et al. 1978) is ˜ 0.4 sq. degrees, and ˜ 1.0 sq. degrees for those in the 4U catalog (Forman et al. 1978). Improvement in these positions has been made over the past two years by the modulation collimators on board the satellites SAS-3 and HEAO-1. In particular, the HEAO-1 scanning modulation collimator has been used to position a total of 20 X-ray sources, confirming the identification in each case, with the possible exception of Mkn 279 (Dower et al. 1979, Griffiths et al. 1979a). Of the 37 X-ray sources which were discovered prior to the launch of the Einstein Observatory and which have been associated with Type 1 Seyferts, 21 have been positioned to ˜ 1 arc minute, representing an improvement by factors of ˜ 20 to 100 over the previous 2A and 4U error box sizes. Some examples of the error boxes and identifications confirmed with the HEAO-1 scanning modulation collimator are shown in figs. 1 and 2. In fig. 1 both NGC 7213 (Philips 1979) and MCG - 2 - 58 - 22 (Ward et al. 1978) were discovered to be Seyferts by optical spectroscopy of candidate objects in the error regions of the corresponding X-ray sources. NGC 7213 is a Seyfert nucleus in a galaxy of Type SO (Philips 1979). In fig. 2, NGC 931 was likewise discovered to be a Seyfert as a result of its X-ray emission (Ward and Wilson 1978).