Rudolf von Thierstein im Sisgau, ca. 1048

In some on-line genealogies a "Rudolf von Thierstein, Graf/Landgraf im
Sisgau" is shown, with death after 1048, and up to three sons:

* Rudolf (II) von Thierstein, m. Ita Habsburg, d. after 1114

* Rudolf von Honberg, Bishop of Basel, d. 1122

* Heinrich von Thierstein, Sire of Lastic, m. Albéarde de Mercoeur

These three "sons" seem to be historic, but does their "father" Rudolf
im Sisgau have any factual basis at all? I have zero idea how to
address this question and hope someone here can shed light.

One relevant page might be
http://www.burgenwelt.de/dickemauern/altenberg/geke.htm
(This page is in German. I can load it and cut-and-paste the contents
into Google Translate, though if I click "Translate this Page from
Google Search I seem to get a different page.)

Another source, cited by one of the on-line genealogies, is

F.Freytag v.Loringhoven (D.Schwennicke, Hrsg.): Europ"aische
Stammtafeln, Band V, Tafel 131. Marburg, 1978
D.Schwennicke: Europ"aische Stammtafeln, Vol. XI, Tafeln 132. Marburg,
1986

I have a (provocative?) follow-on question, but needn't bother with it
now, since I'm not sure Rudolf im Sisgau even existed at all! :-)

James
.