Laravel 5.1: Accessor method for created_at date not working

Following is route:

$router->get('/securityquestionlist', [ 'as'=> 'SecurityQuestionListIndexRoute', 'uses'=> 'SecurityQuestionListController@index']);

I have following action in controller class:

public function index()
{
    $model = new SecurityQuestionListModel();

    $data = $model->select('question','created_at', 'updated_at', 'status')->where('status', 1)
            ->orderBy('created_at', 'desc')
            ->paginate(3);

if(Request::ajax()){
        return response()->json(['rData' => $data]);
    }else{
        return view('securityquestionlist.index' /* ,['rData'=> $data]*/ );
    }

Following is Ajax code:

<script type="text/javascript">
    jQuery(document).ready(function() {
        jQuery('#IdSQLTable').DataTable({
            'ajax'  : 'http://localhost:9901/securityquestionlist',
            'cache' : false

        });
    } );
</script>

I am receiving following AJAX response from server:

{"rData":{}}

Can some one guide me, in case of AJAX why $data value is not returning from server. If I disable ajax, and load normal page then value is received on client side and table rows are populated with data. Right now I have made it remarks in :

return view('securityquestionlist.index' /* ,['rData'=> $data]*/ );

via Chebli Mohamed