分类： 天文学 >> 天文学 提交时间： 2023-12-29
Pei Wang
Jian Li
Long Ji
Xian Hou
Erbil Gugercinoglu
Di Li
Diego F. Torres
Yutong Chen
Jiarui Niu
Weiwei Zhu
Bing Zhang
En-wei Liang
Li Zhang
Mingyu Ge
Zigao Dai
Lin Lin
Jinlin Han
Yi Feng
Chenhui Niu
Yongkun Zhang
摘要： Magnetars are neutron stars with extremely strong magnetic fields, frequently powering high-energy activity in X-rays. Pulsed radio emission following some X-ray outbursts have been detected, albeit its physical origin is unclear. It has long been speculated that the origin of magnetars' radio signals is different from those from canonical pulsars, although convincing evidence is still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and its associated Fast Radio Burst (FRB) 20200428, a radio pulsar phase was discovered. Here we report the discovery of X-ray spectral hardening associated with the emergence of periodic radio pulsations from SGR 1935+2154 and a detailed analysis of the properties of the radio pulses. The complex radio pulse morphology, which contains both narrow-band emission and frequency drifts, has not been seen before in other magnetars, but is similar to those of repeating FRBs - even though the luminosities are many orders of magnitude different. The observations suggest that radio emission originates from the outer magnetosphere of the magnetar, and the surface heating due to the bombardment of inward-going particles from the radio emission region is responsible for the observed X-ray spectral hardening.
分类： 天文学 >> 天文学 提交时间： 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
摘要： 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.
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