A major milestone for the NuSTAR mission was reached last week with the approval of automated systems that will reduce the response time to Target-of-Opportunity (ToO) triggers from 48 hours to less than 6 hours. The number of ToO proposals submitted to NuSTAR to study transient phenomena has steadily increased over the last decade and the mission has responded by expanding the allocation of ToO time. This year, more than 40% of all proposals selected for NuSTAR investigations are for ToO observations of transient events such as supernova explosions, gravitational wave afterglows, outbursts from black hole binary star systems, and counterparts to neutrino detections. Up until now, the response to the triggering of these observations has been a manual process, involving operations teams at the Science Operations Center (SOC) at Caltech and the Mission Operations Center (MOC) at UC Berkeley. A rapid response to transient events has only been possible during working hours and on a few occasions when staff had been available on evenings and weekends. However, over the last few years, automated systems have been developed at the SOC and MOC which will enable generation and upload to the spacecraft of a new command sequence containing instructions to observe approved transient targets each time a rapid-response ToO observation is triggered. Once these systems are implemented, we expect that the time from the triggering of an observation to NuSTAR being pointed at the target and collecting science data to be on average less than 6 hours, and in some cases within an hour. This is a major adjustment to the standard operation of the mission and so a Change Control Board (CCB) meeting was held at Caltech last week for the MOC and SOC teams to present the systems to the NuSTAR Principal Investigator, Project Manager, Mission Assurance Manager, and Project Scientist. Approval of the new systems was given by the CCB to make the systems operational with some minor modifications, and we plan to announce this new capability to the community later this month.

Authors: Karl Forster (NuSTAR Science Operations Manager)