facebook php sdk automatically logs out user - facebook

Question

I am trying to integrate facebook login in my website.
I am facing a weird problem wherein the user keeps getting logged out almost every 10 minutes from my website, although he remains logged in to facebook:
I don't have much clue about the cause of the error, but this might help. I had some error in my javascript code and since during that time, javascript was not being executed, I somehow remained logged in.
For implementing facebook login i am using geloginUrl and getLogoutUrl functions in php, I have added some code to post on friends' wall etc in javascript as well.
That is all the relevant information according to me.
Let me know, if any additional details might be required to answer this question correctly.
This is what my code looks like:
$user = $facebook->getUser();
if ($user) {
try {
$user_profile = $facebook->api('/me');
} catch (FacebookApiException $e) {
$user = 0;
}
}
if ($user) {
setcookie('uid', $user, time()+36000, '/', 'mywebsite.com');
setcookie('uname', $user_profile['name'], time()+36000, '/', 'mywebsite.com');
} else {
setcookie('uid', $user, time()+36000, '/', 'mywebsite.com');
setcookie('uname', $user_profile['name'], time()+36000, '/', 'mywebsite.com');
}
$loginUrlParams = array(
'scope' => 'email,user_activities,friends_activities,friends_interests,user_interests',
'redirect_uri' => 'http://mywebsite.com/getfbToken.php'
);
$loginUrl = "";
$logoutUrl = "";
$logoutUrlParams = array( 'next' => 'http://mywebsite.com/logout.php' );
// getting login url from facebook if user is invalid
if (!$user)
$loginUrl = $facebook->getLoginUrl($loginUrlParams);
else
$logoutUrl = $facebook->getLogoutUrl($logoutUrlParams);