"But if this rise is due to speculation of another takeover...

"But if this rise is due to speculation of another takeover proposal, then that is another scenario altogether."

rae it would seem to me that the likelihood of a new takeover offer is high after this week's trading in particular this mornings significant rise in sp to 63.5c on strong buying while nearly all other stocks are falling including HZN, currently 36.5c.

Someone wants in badly and it surely can't simply be funds buying for the possibility of franked divs post the proposed HZN merger/TO completion or HZN sp would be much higher.
Yodi posted the well researched article, in above post, from the AFR,
which included these references to Fosun Group.

"Edited by Sarah Thompson, Anthony Macdonald and Gretchen Friemann

Rarely a week goes by without another name entering the arena for Roc Oil.
The takeover target has had a string of prospective suitors attached to it, with this column naming a number of suspects. But sources claim the Chinese giant Fosun Group is mulling a bid.
Unlike smaller outfits such as Malaysia’s Hibiscus Petroleum, financial firepower would be no problem. According to those familiar with the matter, Fosun, a broadly diversified, privately held conglomerate, would have to pitch an offer at 70¢ per share to scupper a merger with Horizon Oil.
Under the terms of that deal, a contender for Roc has less than a month to mount a takeover approach and it’s questionable whether Fosun will ultimately have the appetite to enter the public domain with all the scrutiny that would entail.
But some in the market remain sympathetic to the view that Roc Oil’s merger with Horizon represents a mediocre outcome for the Sydney-based exploration company.
The transaction will soak up Roc Oil’s spare cash in return for exposure to the often volatile Papua New Guinea market, where Horizon has a number of exploration projects.
Roc Oil’s Chinese oilfields and its production sharing contracts with China National Offshore Oil Corp and PetroChina make the company an attractive target."

That was weeks ago and by any means things have changed and I'd be surprised if the article's authors still regard a bidder's appetite for a new TO offer as "questionable".

Who knows the last three days strong buying may be all speculation but with over a million each day and nearly all of those at or above 60c, at the very least there is an odd mismatch and arbitrage between the current SPs 64.5c ROC and 36.5c HZN,
ie. 64.5 ROC X .724 = 46.7c HZN