Q: help! kernel panic + 4/MEM/4/40000000: 0xa9f36a18 what's this?

Looks like a bad memory module, you can take it to an Apple genius bar and have them check the MBP and memory, or try installing new memory modules yourself and see if the kernel panic continues...make sure the memory is the right spec for that machine.

Can get that info at http://www.everymac.com

Also get memory info from this knowledge base article.

This is what a kernel panic message looks like:http://support.apple.com/kb/TS3742, and they are often times caused by faulty ram (memory).  See if this troubleshooting article regarding kernel panics is of any value to you: http://thexlab.com/faqs/kernelpanics.html.

Reinstalling the operating system will not do anything if the kernel panic is caused by hardware, a bad memory module.  It would be more productive to simply replace the memory modules.  The least expensive way would be to buy one matching module, then look at the system report on your memory and see if one matches the error code number...replace that module and see if all is well.  If not, replace both modules.

An alternative is to take the MBP to an Apple genius bar and have them check it for you and replace what is bad...Apple memory prices are very high compared with those of trusted suppliers such as Crucial and OWC, http://www.macsales.com

Reinstalling solves nothing, in fact I wonder if you can do that if kernel panics are continuous. Solve kernel panic and then you may reinstall, if need be, usually no need to do that.

In the overwhelming majority of cases, KP means a faulty hardware component.