Seems wild to me that I couldn't find this info in English from the official sources. Here's a shot:
The regional transit authority, VOR, fares are valid on the vast majority of mass transit in the region:
- All trains operated by ÖBB (S-Bahn, Regionalzug, railjet...)
- Underground (U-Bahn) operated by Wiener Linien
- Trams (Straßenbahn, "Bim") operated by Wiener Linien
- City buses operated by Wiener Linien and subcontractors
- Regional buses operated by VOR, Postbus, Badner Bahn and subcontractors
- Badner Bahn interurban railway
You are allowed to take a long distance or regional train within the city or VOR area with a regular VOR fare.
VOR fares do not apply on private and tourist services:
- City Airport Train CAT
- Vienna Airport Lines buses
- Air Liner buses
- Hop-on, hop-off sightseeing buses and trams
- Westbahn trains
- RegioJet trains (not to be confused with ÖBB Regionalzug, Regionalexpress, railjet or cityjet - those are included)
VOR fares recently stopped employing a zone system in favor of point to point pricing.
The key exception is everything in the Vienna city limits - the former zone 100, now simply known as "Kernzone." This zone covers everything in the precise municipal boundary, and occasionally, the first stop outside. For guests and the non-geographically-inclined this is a bit tricky but you can consult this list of stations in each direction you Kernzone ticket is valid to.
The common time-based tickets (such as the 48-hour ticket) are valid for the Kernzone.
Vienna Airport is not in the city limits: this means you need to buy an additional ticket to cover the stretch between the airport and Vienna city limits.
If travelling by S-Bahn this is quite easy: you simply buy a ticket from the Airport (Flughafen Wien) to the suburb Schwechat for €1.80 which is the point from where your 48-hour ticket is valid. The same applies for the return: before boarding the train you'll take directly to the airport (in your case at Zentralfriedhof since that's still in the Kernzone) buy a point to point ticket from Schwechat to Flughafen Wien to cover the portion of your trip that's outside of the area your 48-hour ticket is valid.
If you want to take the railjet or other long distance train from the Airport to Wien Hbf or Meidling you can theoretically buy a ticket "to the city limits" (nach Stadtgrenze) but I'm not sure how on the machines.
There are ticketing machines in the arrivals hall after the exit from baggage claim, and more machines (normally no line) down on the train platform. Theoretically you can buy whichever tickets you need here, but it may be easier to buy the 48-hour ticket in advance on your phone and just do the point to point ticket here. There's no cost savings for advance booking. You are required to have a ticket before boarding the train.