The IPS is onboard the device.
From the spec sheet for the SRX 1400:
"Consolidation of multiple security services into one chassis-based system (IP, GTP, and application firewall; IP and GTP IPS; NAT; IP and application QoS; dynamic routing; application identification, tracking and reporting; and more"
Have a read of this PDF for configuration:
http://kb.juniper.net/library/CUSTOMERSERVICE/technotes/3500146-001-EN.pdf