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Astron. Astrophys. 323, L37-L40 (1997)

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Letter to the Editor

Soft X-ray emission and optical multicolors of faint QSOs in the Selected Area 57

T. Miyaji 1, 2, A.J. Connolly 3, A.S. Szalay 3 and E. Boldt 4

1 Astrophysikalisches Institut, An der Sternwarte 16, D-14482 Potsdam, Germany (present address); (e-mail: tmiyaji@aip.de)
2 Max-Planck-Institut für extraterrestrische Physik, D-85740 Garching b. München, Germany
3 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA (e-mail: ajc@pha.jhu.edu,szalay@pha.jhu.edu)
4 Code 660, NASA Goddard Space Flight Center, MD 20771, USA (e-mail: boldt@lheavx.gsfc.nasa.gov)

Received 24 April 1997 / Accepted 13 May 1997


We present the ROSAT HRI X-ray measurements of 19 spectroscopically confirmed optically-selected QSOs in the 12 [FORMULA] radius region in the Selected Area 57. The optical-to-X-ray spectral index [FORMULA] ranges from 1.25 to 1.7, consistent with brighter QSOs. We have investigated the relationship between soft X-ray emission observed with the ROSAT HRI and optical colors (UJFN) of optically-selected QSOs in SA57. The optical to X-ray spectral index [FORMULA] is found to be correlated with the [FORMULA] color, by a combined effect of [FORMULA] and U, N excess correlations. Possible explanations are the physical link between broad emission-lines/Balmer continuum, and the ionizing radiation source seen in X-ray and/or a geometrical effect.

Key words: Galaxies: active – X-rays: general

Send offprint requests to: T. Miyaji, AIP address

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998