is that so

is that so

Is that really true? Is that a fact? Can be used to indicate simple acknowledgement or surprise, or sarcastically to indicate disbelief. A: "John's got the flu so he'll have to skip this week." B: "Is that so? That's too bad. Tell him I hope he feels better." A: "I'm actually a black belt." B: "Is that so? Wow, I never knew you were so highly trained."
See also: that
Farlex Dictionary of Idioms.

Is that so?

 and Is that right? 
1. Is what you said correct? (With rising question intonation.) Henry: These are the ones we need. Andrew: Is that right? They don't look so good to me. Fred: Tom is the one who came in late. Rachel: Is that so? It looked like Bill to me.
2. That is what you say, but I do not believe you. (No rising question intonation. Slightly rude.) Mary: You are making a mess of this. Alice: Is that so? And I suppose that you're perfect? Bob: I found your performance to be weak in a number of places. Henry: Is that right? I suppose you could have done better?
See also: that
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

is that ˈso?

(informal)
1 used for telling somebody that you are not frightened by their actions or threats: ‘If you don’t shut your mouth I’ll kick you out of the house.’ ‘Is that so? You just try it!’
2 used to express surprise or interest at what somebody has said: ‘He owns twenty cars.’ ‘Is that so?’
See also: that
Farlex Partner Idioms Dictionary
See also:
  • is that right
  • Is that so?
  • Is that a fact?
  • Is that what they're calling it now?
  • Is that what they're calling it these days?
  • come again
  • come again?
  • et alibi
References in classic literature
"You are the owner of this house - I am underneath your roof - is that so?"