Answer:
intensive
Step-by-step explanation:
Himself is an intensive pronoun in this sentence because it emphasizes that Carl Sagan wrote that document all by himself. An intensive pronoun usually is found immediately after the noun that it intensifies. An intensive pronoun can also be removed from the sentence and the sentence will be grammatically correct. If we changed the sentence to "Carl Sagan wrote that document all by himself" himself becomes a reflexive pronoun. It cannot be removed or the sentence will not be grammatically correct.