Search for Ronin Pulsars in Globular Clusters Using FAST: Discovery of Two New Slow Pulsars in M15

Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-29

Dengke Zhou Pei Wang Di Li Jianhua Fang Chenchen Miao Paulo C. C. Freire Lei Zhang Dandan Zhang Huaxi Chen Yi Feng Yifan Xiao Jintao Xie Xu Zhang Chenwu Jin Han Wang Yinan Ke Xuerong Guo Rushuang Zhao Chenhui Niu Weiwei Zhu

Abstract： Globular clusters harbor numerous millisecond pulsars; however, the detection of long-period pulsars within these clusters has been notably scarce. The search for long-period pulsars encounters significant challenges due to pronounced red noise interference, necessitating the crucial step of red noise removal in the data preprocessing. In this study, we use running median filtering to mitigate red noise in multiple globular cluster datasets obtained through observations with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Additionally, we estimated the minimum detectable flux density of pulsars ($S_{ rm min}$) considering this processing step, resulting in a function depicting how $S_{ rm min}$ varies with different duty cycles and periods. Subsequently, a systematic search for long-period pulsars was conducted on the globular cluster datasets after red noise elimination. Ultimately, two isolated long-period pulsars were discovered in the M15 globular cluster, with periods of approximately 1.928451 seconds and 3.960716 seconds, both exhibiting remarkably low pulse duty cycles of around 1 %. Using archived data, we obtained timing solutions for these pulsars. Based on the timing results, their positions are found to be close to the center of the M15 cluster. On the $P- dot{P}$ diagram, they both lie below the spin-up line, suggesting that their recycling process was likely interrupted, leading them to become isolated pulsars. Moreover, in our current search, these very faint long-period pulsars are exclusively identified in M15, and one possible reason for this could be the relatively close proximity and extremely high stellar formation rate of M15. As observational data accumulate and search algorithms undergo iterative enhancements, the prospect of discovering additional long-period pulsars within globular clusters, such as M15, becomes increasingly promising.

Peer Review Status:Awaiting Review

 Hits 407  Downloads 91  Comment