According to The Wrap, who cites sources close to Microsoft, Microsoft will be unveiling a Windows 8 tablet this Monday in LA at an invite-only press event. The tablet is said to be a Microsoft-branded device and will be manufactured by Microsoft itself. The event is set for Monday, June 18 at 3:30 PST.
Rumors are saying that the tablet to be released will run Windows RT, the version of Windows destined for machines with ARM processors. Other specifications of the machine have not been rumored or guessed at, so it's a little hard to say what they will be. They most likely will take aim at the Apple iPad and have a similar size and processor.
After the event we will be able to tell you much more about the device, but until then, you'll have to take this rumor with a grain of salt. Nothing official from the company has confirmed that it is a tablet they are releasing. It could be something else entirely. More after it happens 3:30PST Monday.