jQuery POST与选项

I am trying jQuery Ajax for consuming rest service. Ajax request type is 'POST'. When I am try to load this then request is going as "OPTIONS" and I'm getting "501 Not Implemented" ( as shown in image)

<script>
var user ="user:pwd";
var auth = "Basic " + btoa(user);

    $(function(){
        $.ajax({
            type: 'post',
            url: 'https://xyz/api/core/v3/xyz',
            dataType: 'json',
            contentType: 'application/json',
            data: '{"title":"test","content":"testpega" }',

            success: function(resp) {
                $('#log').html("success");
            },
            error: function(e) {

                $('#log').html("error: "+e);
            }
        });
    });

</script>   

Any help/suggestion ?

Note: I am able to use same webservice with FireFox rest-client add-on.