Speaker
            
    Michael Kachelriess
        
            (NTNU)
        
    Description
I review briefly the story how blazar data were used to set limit lower limits
on space-filling magnetic fields. Then I discuss critically the possibility to
find signatures of helical magnetic fields by this method.
            Author
        
            
                
                
                    
                        Michael Kachelriess
                    
                
                
                        (NTNU)