2020ApJ...900L...7G

With the 12 year long observations by Fermi-LAT, we discover two pairs of spin-down state transitions of PSR J1124-5916, making it the second young pulsar detected to have such behaviors. PSR J1124-5916 shows mainly two states according to its spin-down rate evolution, the normal spin-down state and the low spin-down state. In about 80% of the observation time, the pulsar is in the normal spin-down state, in which the spin-down rate decreases linearly and gives a braking index of 1.98 ± 0.04. The two transitions to the low spin-down state are in MJD 55183-55803 and MJD 56114-56398, respectively, with fractional amplitudes both ∼0.4%. No significant difference between the γ-ray profiles of the two spin-down states is detected, which is similar to PSR B0540-69, the other young pulsar with state transition detected.