Landessternwarte;
Knigstuhl;
D 69117 Heidelberg;
Germany;
USG;
Geismarlandstr. 11;
D 37083 Gttingen;
Germany;
Tuorla Observatory;
FIN 21500 Piikki;
Finland;
USM;
Scheinerstr. 1;
D 81679 München;
Germany;
MPIA;
Knigstuhl 17;
D 69117 Heidelberg;
Germany;
ROE;
Blackford Hill;
Edinburgh EH9 3HJ;
United Kingdom;
PKS; A Lens or Being Lensed; The BL Lac Object PKS 0537-441;