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We present multi-frequency spectra of the Seyfert 1 galaxy H2106-099, fromradio to hard X-rays, spanning over a decade of observations. The hard X-ray(2-20 keV) spectrum measured with Ginga had a Log slope of -0.80 +/- 0.02 on1988 May 18 and -1.02 +/- 0.10 on 1988 May 22 / 23 UT, with no observed fluxchanges. Other measurements showed variability and unusual spectral features:The V band flux changed by a factor of 1.8 (> 10 sigma) in six weeks. Onlymoderate optical Fe II emission is present, but strong [FeVII] and [Fe X] linesare present in some epochs. The Balmer lines show > 25% variations in fluxrelative to the mean, and He I changed by more than 100% relative to the meanin <~ six years. The most surprising finds came from the composite UV throughnear-IR spectrum: If the spectrum is de-reddened by the galactic extinctionvalue (from 21 cm observations), a residual 2175 Angstrom absorption feature ispresent. Additional de-reddening to correct the feature yields E(B-V)=0.07 magdue to material outside our galaxy, most probably associated with the AGN orits host galaxy. No other clear indications of reddening are observed in thisobject, suggesting that blue bump strength measurements in low and intermediatered-shift AGN could be incorrect if derived without UV observations of theregion near 2175 Angstrom in the AGN frame. After all reddening corrections areperformed, the log slope of H2106-099 from the near IR (~12500 Angstrom) to theUV (~1400 Angstrom), -0.94 +/- 0.05, is steep compared to other AGN, suggestingthat the blue bump in this object is intrinsically weak. Weak blue bumps are,therefore, not always an artifact caused by reddening.Comment: Three parts: A. 33 pages text, B. one landscape table, C. 8 figure

The Weak Blue Bump of H2106-099 and Active Galactic Nuclei Dereddening