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Avid recommends a second(separate) hard drive for sessions, but it doesn't NEED to be external(many laptops can hold a second internal drive). Your laptop is fairly new, it probably has a few USB3 ports, which is plenty fast enough for an external drive with either a 7200 rpm spinner, or an SSD. Beyond that, if the system drive is a fast SSD(Samsung 840/850 are excellent), then you can probably get away with storing sessions on the C: drive(even though its not recommended), but consider a few details:
1-SSD's are fast, but usually not very large(capacity), so filling the system drive up with a lot of sessions is not a good idea.
2-recording to a separate drive gives best performance(and performance is not something we will ever have too much of)
3-no matter what drive you record to; don't let it get too full(best to leave 15-20% of free space).
4-system backup is ALWAYS a good plan. So I recommend you buy a big(like 4-5TB) external drive and use it for copies of all your sessions, AND a folder for storing "drive images". A drive image is a complete "snapshot) of a hard drive(like your system drive). If you save an image when your new computer has all your PT and plugins installed and running greate for a month or two, then if something bad happens(like a virus, trojan, drive crash or some update or new plugin trashes your rig, restore to the image you saved and skip needing to do a full re-install of all your software and OS)
Just my opinion
