I cannot find a site stating what the AT or TXS star/astronomy catalogues are, even though some AT and TXS 'events' have been in the news lately....
"AT" are sources named by the transient name server:
A name of the form, e.g. 2016ab, defines the object uniquely. Before it is spectroscopically classified it will have a prefix of "AT". If classified as a SN of whichever type, the prefix changes to "SN".
"TXS" are sources from the Texas Survey of radio sources:
The name is constructed from the hours and minutes of right ascension, the sign of declination, and truncated tenths of degrees of declination: hhmmsddd. Suffixes 'A', 'B', etc., are also used in cases where close sources would otherwise have duplicate names, e.g., 'TXS 0001-234A' and 'TXS 0001-234B'.