Change/Modify the timestamp into GMT format in PHP

/ ** Change/Modify the timestamp into GMT date time format.
* e.g. Thu, 02 Dec 2010 18:34:11 GMT * /

$today_timestamp= mktime(0, 0, 0, date("m") , date("d"), date("Y"));
// Changing the time stamp into GMT format
$get_GMT_format = gmdate('D, d M Y H:i:s T', strtotime($today_timestamp));