Eur. Med. 1143 ἑσπόμην aor. of ἕπομαι where is the σ from?

Greek Learning Greek
1

In the aorist form ἑσπόμην from ἕπομαι “I am following”, where is the sigma from?
Is the aorist of this verb suppletive?

The question arises while reading:

2

*σεπ-ομαι > ἕπ-ομαι, cf. Lat. sequor (-π- in ἕπομαι is the reflex of earlier labiovelar -qu-)

The aor. stem is zero grade σπ- ; the rough breathing may be due to analogy with the present, or else reduplication, *σε-σπ-ομην > ἑσπόμην.