Actually, "immediately" is an illogical hyperbole. It did not appear out of thin air, but took some small bit of time to get there. "Quickly" or "very soon" would be better.
That's really a question about English. Since "immediately" seems to point to a definite time in the past, the simple past seems right. The present perfect doesn't have that feature but talks about the past from the point of view of the present. At least that's what these guys think: http://www.englishclub.com/grammar/verb-tenses_present-perfect_u.htm