It has been a busy month for the NuSTAR observatory. NuSTAR has in the past performed on average six Target of Opportunity (ToO) observations each month, but the numbers have been steadily increasing over the summer, in part because the Sun has moved away from the position on the sky of the Galactic center, a particularly active part of the sky. So far this month there have been 22 ToO submissions to NuSTAR, five of which were ToO proposals from the Guest Observer (GO) program, and a further five approved Director's Discretionary Time proposals—a new record for time-domain observation requests! More than half of these have been requests to observe transient sources within 5 degrees of the Galactic center, including observations for three GO programs of a bright, previously unknown transient X-ray source, MAXI J1750-327, coordinated with NASA's IXPE mission. Other ToO requests have taken advantage of the new policy allowing short NuSTAR exposures, either splitting up GO observations to increase the number of visits or performing brief monitoring visits to well-known X-ray binaries to keep track of their behavior and to alert the community when an expected outburst begins. Up until recently, the Swift mission has performed the majority of this kind of monitoring. The increase in NuSTAR time domain observations will help to cover some of this lost capability, but it will not be able to replace the key role Swift has played in the X-ray astronomy ecosystem. We salute the Swift team for their extraordinary work over the past decades and the great teamwork the Swift and NuSTAR observatories have been able to achieve together, and wish them the best in their final months of operations.

Author: Karl Forster (NuSTAR Science Operations Lead, Caltech)