Three Pulsars Discovered in Globular Cluster M15 (NGC 7078) with FAST

摘要: We present the discovery of three pulsars in Globular Cluster M15 (NGC 7078) by the Five-hundred-meter Aperture Spherical radio Telescope (FAST).
In the three pulsars, PSR~J2129+1210J (M15J) is a millisecond pulsar with a spinning period of 11.84 ms and a dispersion measure of 66.68 pc cm$^{-3}$.
Both PSR~J2129+1210K and L (M15K and L) are long period pulsars with spinning periods of 1928 ms and 3961 ms, respectively, 
while M15L is the GC pulsar with the longest spinning period till now.
The discoveries of M15K and L support the theory that core-collapsed Globular Clusters may contain partially recycled long period pulsars citep{verbunt-2014-slowpulsar}.
With the same dataset, the timing solutions of M15A to H were updated, 
and the timing parameter P1 of M15F is different from the previous results, which is approximately 0.027$ times 10^{-18} ss^{-1}$ from our work and $0.032 times 10^{-18} ss^{-1}$ from Anderson's citep{anderson-1993}. 
As predicted by Rodolfi et al. citep{ridolfi-2017}, 
the luminosity of M15C kept decreasing and the latest detection in our dataset is on December 20$^{ rm th}$, 2022.
We also detected M15I for one more time.
The different barycentric spin periods indicate that this pulsar should locate in a binary system, 
manifesting itself as the exceptional one in such a core-collapsing GC.