unexpected reboot

lastx

root@app1:/var/log# last -x
web-tech pts/0        10.91.0.161      Fri Jul  6 11:24   still logged in   
web-tech pts/1        10.91.0.161      Thu Jul  5 16:51 - 17:25  (00:34)    
web-tech pts/0        10.91.0.161      Thu Jul  5 15:00 - 17:25  (02:24)    
web-tech pts/0        10.91.0.161      Thu Jul  5 14:46 - 14:54  (00:08)    
runlevel (to lvl 2)   3.2.0-26-generic Thu Jul  5 14:33 - 16:39 (1+02:05)   
reboot   system boot  3.2.0-26-generic Thu Jul  5 14:33 - 16:39 (1+02:05)   
shutdown system down  3.2.0-24-generic Thu Jul  5 14:33 - 14:33  (00:00)    
runlevel (to lvl 6)   3.2.0-24-generic Thu Jul  5 14:33 - 14:33  (00:00)    
web-tech pts/1        10.91.0.161      Tue Jul  3 17:36 - 17:42  (00:05)    
web-tech pts/0        10.91.0.161      Tue Jul  3 14:19 - 17:50  (03:30)    
web-tech pts/0        10.91.0.161      Tue Jul  3 10:25 - 10:34  (00:09)   

varlogsyslog

Jul  5 14:26:10 app1 postfix/qmgr[1255]: 63A457F973: from=<www-data@app1.comms.marsdd.com>, size=8103, nrcpt=1 (queue active)
Jul  5 14:26:10 app1 postfix/smtp[20523]: 63A457F973: to=<marsportal@marsdd.com>, relay=mail.marsdd.com[10.101.1.139]:25, delay=0.25, delays=0.02/0.01/0.01/0.21, dsn=2.6.0, status=sent (250 2.6.0 <c90e9049743d6f41a8678860f6ece2cc@www.marsdd.com> [InternalId=628495] Queued mail for delivery)
Jul  5 14:26:10 app1 postfix/qmgr[1255]: 63A457F973: removed
Jul  5 14:33:15 app1 kernel: [3695684.599182] init: tty4 main process (1000) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.599677] init: tty5 main process (1007) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.600112] init: tty2 main process (1020) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.600586] init: tty3 main process (1021) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.601057] init: tty6 main process (1023) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.601902] init: cron main process (1026) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.602495] init: irqbalance main process (1041) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.602828] init: tty1 main process (1622) killed by TERM signal
Jul  5 14:33:15 app1 kernel: [3695684.724326] init: plymouth-upstart-bridge main process (21478) terminated with status 1
Jul  5 14:33:15 app1 kernel: Kernel logging (proc) stopped.
Jul  5 14:33:15 app1 rsyslogd: [origin software="rsyslogd" swVersion="5.8.6" x-pid="920" x-info="http://www.rsyslog.com"] exiting on signal 15.
Jul  5 14:33:40 app1 kernel: imklog 5.8.6, log source = /proc/kmsg started.
Jul  5 14:33:40 app1 rsyslogd: [origin software="rsyslogd" swVersion="5.8.6" x-pid="902" x-info="http://www.rsyslog.com"] start
Jul  5 14:33:40 app1 rsyslogd: rsyslogd's groupid changed to 103
Jul  5 14:33:40 app1 rsyslogd: rsyslogd's userid changed to 101
Jul  5 14:33:40 app1 rsyslogd-2039: Could not open output pipe '/dev/xconsole' [try http://www.rsyslog.com/e/2039 ]
Jul  5 14:33:40 app1 kernel: [    0.000000] Initializing cgroup subsys cpuset
Jul  5 14:33:40 app1 kernel: [    0.000000] Initializing cgroup subsys cpu
Jul  5 14:33:40 app1 kernel: [    0.000000] Linux version 3.2.0-26-generic (buildd@batsu) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #41-Ubuntu SMP Thu Jun 14 17:49:24 UTC 2012 (Ubuntu 3.2.0-26.41-generic 3.2.19)
Jul  5 14:33:40 app1 kernel: [    0.000000] Command line: BOOT_IMAGE=/vmlinuz-3.2.0-26-generic root=/dev/mapper/varnish1-root ro quiet splash
Jul  5 14:33:40 app1 kernel: [    0.000000] KERNEL supported cpus:
Jul  5 14:33:40 app1 kernel: [    0.000000]   Intel GenuineIntel
Jul  5 14:33:40 app1 kernel: [    0.000000]   AMD AuthenticAMD
Jul  5 14:33:40 app1 kernel: [    0.000000]   Centaur CentaurHauls
Jul  5 14:33:40 app1 kernel: [    0.000000] Disabled fast string operations