Presentation #116.61 in the session Stellar/Compact Objects.
We report on our monitoring of the strong-field magnetar-like pulsar PSR J1846-0258 with the Neutron Star Interior Composition Explorer (NICER) and the timing and spectral evolution during its outburst in August 2020. Phase-coherent timing solutions were maintained from March 2017 through November 2021, including a coherent solution throughout the outburst. We detected a large spin-up glitch of magnitude ∆ν/ν = 3 × 10-6 at the start of the outburst and observed an increase in pulsed flux that reached a factor of more than 10 times the quiescent level, larger than that of the 2006 outburst. Our monitoring observations in June and July 2020 indicate that the flux was rising prior to the SWIFT announcement of the outburst on August 1, 2020. We also observed several sharp rises in pulsed flux following the outburst and the flux reached quiescent level by November 2020. The pulse profile was observed to change shape during the outburst, returning to the pre-outburst shape by 2021. Fitting combined NICER and NuSTAR spectra with a black-body plus power law shows that the black-body dominates during the flux peaks of the outburst while the power law dominates during periods of lower flux and quiescence. We discuss the interpretation of the magnetar-like outburst in the context of both a pulsar-like and a magnetar-like model.