How to escape square bracket in Logstash Grok filter?

[pjanzen (Paul Janzen)]

@elasticheart

\t[05/Feb/2018:10:39:47 +0000]\t

This seems to work for me.
\\t\[%{GREEDYDATA:timestamp}\]\\t

on http://grokdebug.herokuapp.com/ it gives me the below result.

{
  "timestamp": [
    [
      "05/Feb/2018:10:39:47 +0000"
    ]
  ]
}