about 3.13... I noticed that stuff lying around, and purged images and headers related to old kernel. Reproduced problem afterward.
by the way... I it crashed just now again, I wasn´t in anything graphics intensive, it had stayed up for about three hours, but I was just browsing, and building the bug report (running Unity 7... the normal ubuntu desktop.)
root@alu:/alu/sdc1/home/peter# journalctl -b -1
Specifying boot ID has no effect, no persistent journal was found
root@alu:/alu/sdc1/home/peter# uname -a
Linux alu 4.4.0-14-generic #30-Ubuntu SMP Tue Mar 15 13:04:17 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
root@alu:/alu/sdc1/home/peter# dpkg -l | grep linux-image
ii linux-image-4.4.0-14-generic 4.4.0-14.30 amd64 Linux kernel image for version 4.4.0 on 64 bit x86 SMP
ii linux-image-extra-4.4.0-14-generic 4.4.0-14.30 amd64 Linux kernel extra modules for version 4.4.0 on 64 bit x86 SMP
ii linux-image-generic 4.4.0.14.15 amd64 Generic Linux kernel image
root@alu:/alu/sdc1/home/peter#