FORTUNE — “Our weekly iPhone sales continue to be impacted by rumors and speculation regarding new products,” Apple AAPL CEO Tim Cook told analysts last Tuesday even as his company’s share price was plummeting. Apple’s iPhone sales had fallen short of expectations, and the Street was punishing the stock.

But rumors and speculation can also drive Apple shares in the other direction, and that’s what seems to be happening this week.

On Monday morning, iMore‘s Rene Ritche posted that he’d heard “from sources who have proven accurate in the past,” that Apple was planning to unveil a new iPhone, and maybe an iPad mini and an updated iPod, at a special event on Wednesday, Sept. 12, 2012 — a rumor picked up and retailed to their readers by more than three dozen other tech reporters.

The Sept. 21 iPhone date — which was earlier than many had expected — was “confirmed” a few hours later by John Paczkowski on AllThingsD, a site owned by the Wall Street Journal, and passed along to clients by several Wall Street Analysts, including Topeka Capital’s Brian White, and, by Tuesday morning, Morgan Stanley’s Katy Huberty.

Result: Apple shares rose $9.87 (1.7%) on Monday and were up more than $7.70 (1.3%) in pre-market trading Tuesday. That would bring them back to roughly where they were before last Tuesday’s quarterly report.

UPDATE: Apple closed at $610.76, up $15.73 (2.64%) on a day that the Dow fell 0.49%.

Die by the iPhone rumor, live by the iPhone rumor.