The picture shows a 1800 s R-band exposure of the object RGB 1745+398 obtained at the 2.6m Nordic Optical Telescope. The field size is 207" x 209". The bright reddish object to the lower left of the center is a BL Lac object at the center of a cluster of galaxies. The blue, arclike structure about 8" southeast of the BL Lac is interpreted as a gravitationally enhanced image of a background galaxy.
RGB 1745+398 was identified as a BL Lac object by Laurent-Muehleisen et al. (1998) in optical follow up observations of a correlation between the ROSAT All Sky Survey and the Green Bank 5 GHz radio survey (Brinkmann et al. 1995). The discovery of the arclike structure was presented by Nilsson et al. (1999).
The location of this nearby BL Lac object (z = 0.267) in the
center of a cluster suggests that some portion of the X-ray emission
is coming from the intra-cluster gas.
This object nicely illustrates the commonly found
close relationship between
Active Galactic Nuclei and Clusters of Galaxies.
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The ROSAT AGN content of the 87GB 5 GHz Survey:
Bulk properties of previously optically identified sources:
W. Brinkmann, J. Siebert, W. Reich, E. Fürst, P. Reich,
W. Voges, J. Trümper, R. Wielebinski,
A&A Suppl. 109, 147 (1995)
Radio-loud active galaxies in the northern ROSAT All-Sky Survey. III.
New spectroscopic identifications from the RASS-Green Bank BL Lacertae
survey: S.A. Laurent-Muehleisen, R.I. Kollgaard,
R.B. Ciardullo, E.D. Feigelson, W. Brinkmann, J. Siebert,
ApJS 118, 127 (1998)
The discovery of a blue arc near the BL Lac object RGB 1745+389:
K. Nilsson, T. Pursimo, A. Sillanpää, J. Heidt,
S.J. Wagner, S.A. Laurent-Muehleisen, W. Brinkmann,
A&A 343, 81 (1999)
![[red line]](line-thin-rainbow.gif)
References: