Pulsar search incubated a series of revolutionary discoveries including binary pulsars, millisecond pulsars, extrasolar planets, massive neutron stars, fast radio bursts (FRBs), and etc. In a recent publication, Zhichen Pan, a PhD candidate in NAOC, along with his supervisor, Prof. Di Li, lead scientist of the “ISM evolution and star formation” group, have discovered two new millisecond pulsars in the 47 Tucanae (NGC 104) globular cluster, named as J0024-7204aa and J0024-7204ab, with their newly developed incoherent stacking method. This work is based on the long term monitoring data (~1100 hours over more than 10 years) provided by Dr. George Hobbs, a senior scientist from Commonwealth Scientific and Industrial Research Organization of Australia (CSIRO) and currently a fellow of CAS President International Fellowship Initiative (PIFI).
This is the first time that a China-based scholar has led a discovery of radio pulsars. The work is published in MNRAS (2016, 459, L26-L30, http://mnrasl.oxfordjournals.org/content/459/1/L26), increasing the number of known pulsars in NGC 104 from 23 to 25. The other NAOC co-author is Dr. Pei Wang, also a member of the ISM group. One of the newly discovered pulsars, J0024-7024aa, has the largest dispersion measure as well as the shortest spin period (1.84 milliseconds) among all the pulsars in NGC 104. Such a spin period ranks 12th among all the radio pulsars.
Globular clusters are rich in millisecond pulsars and binaries, thus are important targets for the upcoming observation with the FAST telescope. One of the main early observing mode for FAST will be drift-scan, wherein a globular cluster will be repeatedly covered. The segmented search method developed in this study can improve the FAST’s capability for detecting pulsars in the drift-scan mode. The members in the ISM and the FAST group have already quantified the detectability of the pulsars in the FAST drift-scan mode and are developing the processing pipeline incorporating the segmented search method. The details will be reported in separate articles.
For a more intuitive presentation of the newly discovered pulsars in 47 Tucanae, the pulsar signals were down sampled in frequency by a factor of 80 to produce audible waves. The sound volume varies proportionally to the pulse amplitudes in averaged pulse profile. The central tone of the “pulsar music” was set in C major and a tempo of 4/4. The chirp tune from high to low represents the time delay of the pulsar signals due to the dispersion when the signals are transmitting through the interstellar medium. The percussions are all produced from signals of other 47 Tucanae pulsars. The music presents an artistic view of the waves from the spinning neutron stars, J0024-7204aa and J0024-7204ab, twinkling in 47 Tucanae Cluster far far away, traveling through a glittering, translucent, and romantic starry night. (Music Producer: Yuan Mei at http://ism.bao.ac.cn/resources/pulsar_music/)
Averaged pulse profiles and positions of new pulsars. Left panel is an optical image from 12.5 inch telescope with exposure time 90 min. Registar counts 17,012 stars in this image. The top right panels are averaged pulse profile and intensity versus phase for PSR J0024−7204aa (left) and PSR J0024−7204ab (right). The lower panel is the positions of PSR J0024−7204ab (red point) and the other pulsars (blue point) of 47 Tucanae with known timing solutions. The positions of PSR J0024−7204aa is uncertain in terms of existing data.