Facebook user_online_presence scope

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C#

Facebook-API

Hi,
I am trying to write a code to login to my website using Facebook. I have managed to login and fetch user details using following code:

Response.Redirect(@"https://graph.facebook.com/oauth/authorize?client_id=" +
             facebookClientId + "&redirect_uri=http://" + host +
             @"/FBcallback.aspx&scope=email,publish_stream,offline_access,publish_actions,user_online_presence");

I want to check whether user is online or not i have included the user_online_presence permission . So when user grants me the permission and i have the access token how can I check whether he is online or not?