Discovery of Delayed Spin-up Behavior Following Two Large Glitches in the Crab Pulsar, and the Statistics of Such Processes
Authors: Ge M. Y. , Zhang S. N. , Lu F. J. , Li T. P. , Yuan J. P. , Zheng X. P. , Huang Y. , Zheng S. J. , Chen Y. P. , Chang Z. , Tuo Y. L. , Cheng Q. , Güngör C. , Song L. M. , Xu Y. P. , Cao X. L. , Chen Y. , Liu C. Z. , Zhang S. , Qu J. L. , Bu Q. C. , Cai C. , Chen G. , Chen L. , Chen M. Z. , Chen T. X. , Chen Y. B. , Cui W. , Cui W. W. , Deng J. K. , Dong Y. W. , Du Y. Y. , Fu M. X. , Gao G. H. , Gao H. , Gao M. , Gu Y. D. , Guan J. , Guo C. C. , Han D. W. , Hao L. F. , Huo J. , Jia S. M. , Jiang L. H. , Jiang W. C. , Jin C. J. , Jin J. , Jin Y. J. , Kong L. D. , Li B. , Li D. , Li C. K. , Li G. , Li M. S. , Li W. , Li X. , Li X. B. , Li X. F. , Li Y. G. , Li Z. W. , Li Z. X. , Liu Z. Y. , Liang X. H. , Liao J. Y. , Liu G. Q. , Liu H. W. , Liu X. J. , Liu Y. N. , Lu B. , Lu X. F. , Luo Q. , Luo T. , Ma X. , Meng B. , Nang Y. , Nie J. Y. , Ou G. , Sai N. , Shang R. C. , Song X. Y. , Sun L. , Tan Y. , Tao L. , Wang C. , Wang G. F. , Wang J. , Wang J. B. , Wang M. , Wang N. , Wang W. S. , Wang Y. D. , Wang Y. S. , Wen X. Y. , Wen Z. G. , Wu B. B. , Wu B. Y. , Wu M. , Xiao G. C. , Xiao S. , Xiong S. L. , Xu Y. H. , Yan W. M. , Yang J. W. , Yang S. , Yang Y. J. , Yang Y. J. , Yi Q. B. , Yin Q. Q. , You Y. , Yue Y. L. , Zhang A. M. , Zhang C. M. , Zhang D. P. , Zhang F. , Zhang H. M. , Zhang J. , Zhang T. , Zhang W. C. , Zhang W. , Zhang W. Z. , Zhang Y. , Zhang Y. F. , Zhang Y. J. , Zhang Y. , Zhang Z. , Zhang Z. , Zhang Z. L. , Zhao H. S. , Zhao X. F. , Zheng W. , Zhou D. K. , Zhou J. F. , Zhou X. , Zhuang R. L. , Zhu Y. X. , Zhu Y. 
Published: June 2020

Abstract
Glitches correspond to sudden jumps of rotation frequency (ν) and its derivative (

) of pulsars, the origin of which remains not well understood yet, partly because the jump processes of most glitches are not well time-resolved. There are three large glitches of the Crab pulsar, detected in 1989, 1996, and 2017, which were found to have delayed spin-up processes before the normal recovery processes. Here we report two additional glitches of this pulsar that occurred in 2004 and 2011 for which we discovered delayed spin-up processes, and present refined parameters of the largest glitch, which occurred in 2017. The initial rising time of the glitch is determined as <0.48 hr. The two glitches that occurred in 2004 and 2011 had delayed spin-up time scales (τ
1) of 1.7 ± 0.8 days and 1.6 ± 0.4 days, respectively. We also carried out a statistical study of these five glitches with observed spin-up processes. We find that the Δν versus

relation of these five glitches is similar to those with no detected delayed spin-up process, indicating that they are similar to the others in nature except that they have larger amplitudes. For these five glitches, the amplitudes of the delayed spin-up process (

) and recovery process (Δν
d2), their time scales (τ
1, τ
2), and permanent changes in spin frequency (Δν
p) and total frequency step (Δν
g) have positive correlations. From these correlations, we suggest that the delayed spin-up processes are common for all glitches, but are too short and thus difficult to be detected for most glitches.