when the push notification arrives,
if your application is in the background, -(void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo will be called.
if your application has been terminated, - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions will be called to launch your application in the background.
You can start your issue download accordingly.
NOTE: Make sure you have set up Newsstand requisites properly.
Your "info.plist" has the following keys also
UINewsstandApp
UIBackgroundModes
newsstand-content
You have the following piece of code in your didFinishLaunchingWithOptions: method
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"NKDontThrottleNewsstandContentNotifications"];
This will ensure that the content-available:1 notification is received by the app every time iOS receives it in the development mode only. Usually only one such notification per app(newsstand app) per day is allowed when the app is in App Store.