How to create a tabbed view in a panel without a menu entry?
You don't need 3 views, just create one view with 3 pages Votes, Activity and Newest. define your fields and filters. In Page Settings -> Menu Option, Use the Menu tab. 

Edit: Exmaple

If Page Path for main view is mylist  


Add Pages in View with Paths mylist/votes, mylist/activity,
mylist/newest for all the 3 pages respectively
Select Menu Tab and Provide the Menu for Votes, Activity and Newest respectively




Above was the previous reply, here is answer with some graphics.

For the demo of your use case:


I created a taxonomy vocabulary called DSE with 3 terms Vote, Activity and Newest
I created a new content type called Drupal Stack Exchange, with Title, Questions and Tags field, where Tags field is Term Reference to DSE


In Views, I created a Master Display with Just Title field for demonstration, and I gave the Page path as questions like in this picture



For the Menu for Master display I selected Normal menu entry and selected Main Menu as its menu type:



Then I added the new Page for Activity, and in Path I gave questions/activity



In Menu for Activity, I selected Menu Tab and gave a title called Activity



In Filter for Activity I selected DSE Tag and chosed it to be one of Activity Tag like in the picture below. (Note: While adding filter select only this display)



I repeated the same process for Votes and Newest, as you can see Path settings for Newest is also the Menu Tab like:



Save the view and you'll see the New Menu called Questions in Main Menu, and clicking the Menu will give you 3 tabbed menu inside like:



Note: To make tabbed menu it is required the path to be on the same Path like in above case questions/vote for Vote tab, questions/activity for Activity tab.

Finally the Sneak peak of the View page