A question

I use "./bro -i eth0 tcp.bro -w tom.log" command to save the log to my specific log file-tom.log,but I can only use "./bro -r tom.log" to read it.All other application or viewer such as vi and gedit can NOT read it.Does this because the file format of this log file is NOT ASCII format?Please tell me how to deal with this problem.Thank you.