gc.log should not be application server specific, it's java version/GC used/vendor specific (I would guess tat websphere would be using the IBM JVM)
Examples: https://plumbr.eu/blog/garbage-collection/understanding-garbage-collection-logs
http://stackoverflow.com/questions/895444/java-garbage-collection-log-messages
https://blog.codecentric.de/en/2014/01/useful-jvm-flags-part-8-gc-logging/
https://blog.gceasy.io/2016/07/07/understanding-g1-gc-log-format/
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