Active galaxies observed during the Extreme Ultraviolet Explorer all-sky survey

Details Active galaxies observed during the Extreme Ultraviolet Explorer all-sky survey Active galaxies observed during the Extreme Ultraviolet Explorer all-sky survey

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...439...90m&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 439, no. 1, p. 90-97

Astronomy and Astrophysics

Astronomy

52

Active Galactic Nuclei, Bl Lacertae Objects, Quasars, Seyfert Galaxies, Sky Surveys (Astronomy), Ultraviolet Spectra, Extreme Ultraviolet Explorer Satellite, Spectral Correlation, Spectrum Analysis

Scientific paper

We present observations of active galactic nuclei (AGNs) obtained with the Extreme Ultraviolet Explorer (EUVE) during the all-sky survey. A total of 13 sources were detected at a significance of 2.5 sigma or better: seven Seyfert galaxies, five BL Lac objects, and one quasar. The fraction of BL Lac objects is higher in our sample than in hard X-ray surveys but is consistent with the soft X-ray Einstein Slew Survey, indicating that the main reason for the large number of BL Lac objects in the extreme ultraviolet (EUV) and soft X-ray bands is their steeper X-ray spectra. We show that the number of AGNs observed in both the EUVE and ROSAT Wide Field Camera surveys can readily be explained by modelling the EUV spectra with a simple power law in the case of BL Lac objects and with an additional EUV excess in the case of Seyferts and quasars. Allowing for cold matter absorption in Seyfert galaxy hosts drive up the inferred average continuum slope to 2.0 +/- 0.5 (at 90% confidence), compared to a slope of 1.0 usually found from soft X-ray data. If Seyfert galaxies without EUV excesses form a significant fraction of the population, then the average spectrum of those with bumps should be even steeper. We place a conservative limit on neutral gas in BL Lac objects: NH less than 1020/sq cm.

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