We present evidence for three spin-down glitches ( or ‘ anti-glitches ’ ) in the ultraluminous accreting X-ray pulsar NGC 300 ULX-1 in timing observations made with the Neutron Star Interior Composition Explorer ( NICER ) .
Our timing analysis reveals three sudden spin-down events of magnitudes \Delta \nu = -23 , -30 , and -43 \mu Hz ( fractional amplitudes \Delta \nu / \nu = -4.4 , -5.5 , and -7.7 \times 10 ^ { -4 } ) .
We determined fully phase-coherent timing solutions through the first two glitches , giving us high confidence in their detection , while the third candidate glitch is somewhat less secure .
These are larger in magnitude ( and opposite in sign ) than any known radio pulsar glitch .
This may be caused by the prolonged rapid spin-up of the pulsar causing a sudden transfer of angular momentum between the superfluid and non-superfluid components of the star .
We find no evidence for profile or spectral changes at the epochs of the glitches , supporting the conclusion that these are due to the same process as in normal pulsar glitches , but in reverse .