Responding to 401 unauthorized on SIP notify request

People, I am sending a SIP NOTIFY to a Linksys PAP2T device using the asterisk 1.4.17 sip notify command. The Linksys reply with a 401 challenge command. How can I get asterisk to respond to the challenge. Now, there is a subtlety here, normally asterisk will respond with a 401 to a SIP REGISTER that was not authenticated OR asterisk will respond to a SIP REGISTER 401 response when it tries to register to an external SIP service using the register statement in the sip.conf global section. Those two ops are different from my request here where asterisk sends a SIP NOTIFY and the ATA respond with a 401. Is asterisk designed to respond to a 401 on a SIP NOTIFY or just to a SIP REGISTER?