Radio detection of an elusive millisecond pulsar in the Globular Cluster NGC 6397

• Main Authors: Zhang, Lei, Ridolfi, Alessandro, Blumer, Harsha, Freire, Paulo, Manchester, Richard N, McLaughlin, Maura, Kremer, Kyle, Cameron, Andrew D, Zhang, Zhiyu, Behrend, Jan, Burgay, Marta, Buchner, Sarah, Champion, David J, Chen, Weiwei, Dai, Shi, Feng, Yi, Fu, Xiaoting, Guo, Meng, Hobbs, George, Keane, Evan F, Kramer, Michael, Levin, Lina, Li, Xiangdong, Ni, Mengmeng, Pan, Jingshan, Padmanabh, Prajwal V, Possenti, Andrea, Ransom, Scott M, Tsai, Chao-Wei, Krishnan, Vivek Venkatraman, Wang, Pei, Zhang, Jie, Zhi, Qijun, Zhang, Yongkun, Li, Di
• Format: Journal Article
• Language: English
• Published: 16-07-2022
• Subjects: Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.2207.07880

We report the discovery of a new 5.78 ms-period millisecond pulsar (MSP), PSR
J1740-5340B (NGC 6397B), in an eclipsing binary system discovered with the
Parkes radio telescope (now also known as Murriyang), Australia, and confirmed
with the MeerKAT radio telescope in South Africa. The measured orbital period,
1.97 days, is the longest among all eclipsing binaries in globular clusters
(GCs) and consistent with that of the coincident X-ray source U18, previously
suggested to be a 'hidden MSP'. Our XMM-Newton observations during NGC 6397B's
radio quiescent epochs detected no X-ray flares. NGC 6397B is either a
transitional MSP or an eclipsing binary in its initial stage of mass transfer
after the companion star left the main sequence. The discovery of NGC 6397B
potentially reveals a subgroup of extremely faint and heavily obscured binary
pulsars, thus providing a plausible explanation to the apparent dearth of
binary neutron stars in core-collapsed GCs as well as a critical constraint on
the evolution of GCs.