PKS 2155-304

PKS 2155-304 is one of the brightest active galaxies in the sky.

It is a strong emitter from radio to high energy frequencies. PKS 2155-305 is at redshift z = 0.116 (Falomo, Pesce & Treves 1993) and it is one of the brightest and most studied BL Lacs and is often considered the prototype of X-ray selected BL Lacs.

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