VIENNA (Reuters) - Support for Austria s ruling Social Democrats has slipped since a scandal embroiled the party ahead of an Oct. 15 election but they are in a tight battle with the far right for second place, a poll showed on Thursday. Foreign Minister Sebastian Kurz s conservative People s Party had 34 percent ahead of the far right Freedom Party on 27 percent, according to the Research Affairs poll published by tabloid daily Oesterreich. Chancellor Christian Kern s Social Democrats had 22 percent down 2 percentage points but given a margin of error of 4.3 percent second place was too close to call. The Social Democrats said last weekend it was unwittingly involved in two Facebook accounts that made unsubstantiated allegations against Kurz and the party chairman announced his resignation. Details of the scandal were unclear.  The party launched an investigation and a spokesman for the Vienna prosecutor s office said on Thursday it had opened a defamation inquiry against persons unknown based on a complaint by the Social Democrats.  We are conducting an investigation against persons unknown for defamation,  a spokesman for the Vienna prosecutors  office said.  Of course, we must now approach Facebook and ask if they can help us further in seeking out these persons unknown.  Facebook said on Wednesday in response to a request for help from the Social Democrats:  We are assessing the request and will reply once that assessment is complete.      Like many polls in Austria, the online survey carried out from Monday to Wednesday had a relatively small sample size    of 600 people and a wide margin of error. The People s Party shot to first place in opinion polls when Kurz took over as its leader in May. Other parties were on 6 percent or less. 