The Timing and Spectral Properties of the 2022 Outburst of SGR J1935+2154 Observed with NICER

Abstract The magnetar SGR J1935+2154 entered a new active episode on 2022 October 10, with X-ray bursts and enhanced persistent emission. At the tail of a high burst rate interval, lasting several hours, radio bursts were detected, revealing the connection between the X-ray activities and radio emissions. We analyzed observations of SGR J1935+2154 for nearly 3 months, using data from the Neutron Star Interior Composition Explorer. We report the timing and spectral results following the onset of this outburst. In general, the X-ray flux of the persistent emission decays exponentially. While a flare is evident on the light curve, a fast radio burst (FRB) was detected immediately following the peak of this flare. We found a phase jump in the pulse profile, with a deviation of a 0.16 ± 0.03 phase, which is related to the glitch. The spectra are well fit with the combination of a blackbody and a power-law (PL) model. The decay of the outburst is dominated by the drop in the nonthermal component, which also leads to an increase in thermal proportion. The photon index of the PL is inversely correlated with both the unabsorbed flux and the burst rate. We find that unlike the large variety of the persistent emission around FRB 221014, the X-ray properties are very stable when FRBs 221021 and 221201 happened. These results manifest the connection between the glitch, phase jump, X-ray burst, and radio burst, crucial for studying the mutation in twisted magnetic fields and constraining the trigger mechanism of radio bursts.