I just had to look this up from my own comment to a support question on the WordPress codex so I’m posting it here for my future reference. However, this pattern is a good pattern to use when needing to add an activate function call for your plugin.
$activateFunction = 'activateMyPlugin'; // change this; add_action( 'activate_' . preg_replace( '/.*wp-content.plugins./','',__FILE__ ), $activateFunction );