The tcpConnectionClose is from the the CISCO-GENERAL-TRAPS which you can get from http://www.cisco.com/public/mibs. See http://www.cisco.com/warp/public/477/SNMP/snmp_traps.html which will help you understand this in more detail. From the above URL:
snmp--Sends Simple Network Management Protocol (SNMP) notifications. When the snmp keyword is used, you can specify a notification-option value.
This is from the CISCO-GENERAL-TRAPS.my and the notifications are:
enterprise 1.3.6.1.2.1.11
0 coldStart
2 linkDown
3 linkUp
4 authenticationFailure
5 egpNeighborLoss
enterprise 1.3.6.1.4.1.9
0 reload
Note: The following trap is controlled by the notification-type "tty":
1 tcpConnectionClose <----!!!!
You can use either of http://jaguar.ir.miami.edu/~marcus/snmptrans.html OR
http://www.cisco.com/cgi-bin/Support/Mibbrowser/unity.pl to Search/Translate the MIBs/OIDs.