just checking but is it the owner of the sun stroke card that triggers it right? so if u loose a challenge then you activiate it or do u have to win a challenge by four then activite? also does anyone run this in martell deck since many of there cards go with loosing challenges or only in targaryn burn decks

The "you" in a card always refers to its controller - and, unless otherwise specified, a triggered effect can only be triggered by the controller.

In this case, "you", the martell player, can trigger the response after you lose a challenge by 4 or more.