According to multiple (vague) reports, Apple will hold a "mystery" event in New York later this month to discuss something related to media. What might Apple announce? Here, five theories:

1. Digital textbooks for the iPad
"Steve Jobs' biographer Walter Isaacson has indicated several times that one of Jobs' last goals had been to revolutionize textbooks," says Eric Slivka at Mac Rumors. And I hear that Apple spent last month shooting a number of short interviews with executives in the textbook industry. Yep, my sources also say that "this event will focus on iTunes University and Apple in education," says Clayton Morris at his blog. And it's not being held in Silicon Valley, but New York — the center of publishing and textbooks.

2. A self-publishing platform
I've heard that Apple may be "launching a new digital self-publishing platform," says Michael Kozlowski at Good E-Reader. Currently, independent authors have to go through a third party like Smashwords to get their work in Apple's iBookstore. A new system that lets indie authors publish directly to the iBookstore would be "a huge step forward for Apple," and a threat to Amazon, which encourages independent writers to exclusively publish their work through Amazon.

3. A new advertising initiative or hire
Eddie Cue, Apple's SVP of Internet Software and Services, is supposedly involved, says Kara Swisher at All Things D, and he oversees many of the company's media units, including the iTunes Store and iAds. Plus, Apple has been looking for a new chief of mobile advertising since former head, Andy Miller, jumped ship last summer.

4. A makeover for the iBookstore
It's possible that the iBookstore could be getting a "facelift," says Jonny Evans at Computerworld. As is, it lives in the shadow of Kindle's excellent e-bookstore. That "puts Cue under pressure to glam up iBooks with hot, new, and unique — or at the least, deeply useful — features to differentiate Apple from Amazon and the Kindle."

5. Not the iPad 3 or Apple TV
Many believe the new tablet will be announced early this year, says Paul McDougall at Information Week, but "Cue's presence would… indicate that the news is unrelated to the iPad 3." It's also unlikely, adds Swisher, that the mystery event will center on the oft-discussed new Apple TV, rumored to be coming later this year.