FAST’s First Discovery of a Millisecond Pulsar (MSP)

FAST’s First Discovery of a Millisecond Pulsar (MSP)

On 27 Feb. 2018, the Five-hundred-meter Aperture Spherical radio Telescope (FAST), operated by the National Astronomical Observatories, Chinese Academy of Sciences, discovered a radio millisecond pulsar (MSP) coincident with the unassociated gamma-ray source 3FGL J0318.1+0252 in the Fermi Large Area Telescope (LAT) point-source list. It was confirmed by the Fermi-LAT team in reprocessing of Fermi data on April 18th. This is another milestone of FAST.

Radio follow-up of Fermi-LAT unassociated sources is one of the effective ways for finding new pulsars. Previous radio observations, including three epochs with Arecibo in June 2013, failed to detect the MSP. In an one-hour tracking observation with the FAST ultra-wide band receiver, the radio pulses toward 3FGL J0318.1+0252 were detected with a spin period of 5.19 milliseconds, an estimated distance of about 4 thousand light-years, and as potentially one of the faintest radio MSPs. The newly discovered pulsar, now named PSR J0318+0253, is confirmed to be isolated through timing of gamma-ray pulsations. This discovery is the first result from the FAST-Fermi LAT collaboration outlined in a MoU signed between the FAST team and Fermi-LAT team.

Millisecond pulsars is a special kind of neutron stars that rotate hundreds of times per second. It is not only expected to play an important role in understanding the evolution of neutron stars and the equation of state of condense matter, but also can be used to detect low-frequency gravitational waves. The pulsar timing array (PTA) attempts to detect low-frequency gravitational waves from merging supermassive black holes using the long-term timing of a set of stable millisecond pulsars. Pulsar search is the basis of gravitational wave detection. The planned Commensal Radio Astronomy FAST Survey (CRAFTS, arxiv:1802.03709; http://crafts.bao.ac.cn/) is expected to discover many millisecond pulsars and thus will make significant contribution to the PTA experiment.

Kejia Lee, a staff scientist at the Kavli Institute of Astronomy and Astrophysics,  Peking University, said that “This discovery demonstrated the great potential of FAST in pulsar searching, highlighting the vitality of the large aperture radio telescope in the new era. It is a great achievement fo FAST, still under commissioning. (He) looks forward to its full operation soon.”

Renxin Xu, a professor of astronomy at Peking University, said that “Besides their scientific significance, millisecond pulsars also have potential value in other applications. MSP discoveries from FAST will provide better opportunities for scientists and engineers around the world.”

George Hobbs, a staff scientist of the Commonwealth  Scientific and Industrial Research Organisat (CSIRO)of Australia and a member of the Gravitational Wave International Committee (GWIC), said “The international radio-astronomy community is excited about the amazing FAST telescope. The Australian Parkes Telescope helped confirm FAST’s first pulsar discovery and now Fermi Space Observatory is instrumental in FAST’s first millisecond pulsar. FAST will soon discover a large number of millisecond pulsars and I am looking forward to seeing FAST’s contribution to gravitational wave detection.”

FAST will be under commissioning until it reaches the designed specifications and becomes a Chinese national facility.

Fig1. The Gamma-ray sky map and integrated pulse profiles of the new MSP: Upper panel shows the region of the gamma-ray sky where the new MSP is located. Lower panel a) shows the observed radio pulses in a one-hour tracking observation of FAST. Lower panel b) shows the folded pulses from more than 9 years of Fermi-LAT gamma-ray data.

新闻通稿:FAST首次发现并认证毫秒脉冲星

4月18日,中国科学院国家天文台500米口径球面射电望远镜(FAST)首次发现的毫秒脉冲星得到国际认证,这是FAST继发现脉冲星之后的另一重要成果。

通过跟踪伽马射线点源3FGL J0318.1+0252,FAST于2月27日首次发现这颗毫秒脉冲星,并通过FAST与费米伽马射线卫星大视场望远镜(Fermi-LAT)的国际合作认证了此次新发现。

从射电波段对Fermi-LAT未认证点源进行高灵敏度后随观测,确认高能源属性,是发现新脉冲星的有效途径之一。新发现的脉冲星J0318+0253自转周期5.19毫秒,根据色散估算距离地球约4000光年,由FAST使用超宽带接收机进行一小时跟踪观测发现,是至今发现的射电流量最弱的高能毫秒脉冲星之一。国际大型射电天文台曾对其进行过多次脉冲星搜索,比如美国Arecibo望远镜在2013年6月开展的三次定点观测,都未探测到。通过对Fermi-LAT伽马射线数据的后随计时分析证实J0318+0253为孤立毫秒脉冲星,并提高位置精度至亚角秒量级。这是FAST–Fermi-LAT合作组的首个成果。双方将继续合作研究,并开展多波段观测分析。

毫秒脉冲星是每秒自转上百次的特殊中子星,对其研究不仅有望对理解中子星演化、奇异物质状态起到重要作用,而且稳定的毫秒脉冲星是低频引力波探针。脉冲星搜索是进行引力波探测研究的基础,脉冲星计时阵是观测超大质量双黑洞发出的引力波最有效的方法。脉冲星计时阵依赖数十颗计时性质良好的毫秒脉冲星,其样本的扩大、性能的提高起始于脉冲星搜索。此次FAST首次发现毫秒脉冲星,展示了FAST对国际低频引力波探测做出实质贡献的潜力。FAST项目组已经策划的FAST多科学目标同时巡天规划(CRAFTS,arxiv:1802.03709; http://crafts.bao.ac.cn/)将发现大量毫秒脉冲星,大幅度提高脉冲星阵探测引力波的灵敏度。

北京大学科维理天文与天体物理研究所李柯伽研究员表示,此次发现展示了FAST在脉冲星搜寻方面的重大潜力,凸显了大口径射电望远镜在新时代的生命力。Fast望远镜在调试阶段即取得这样的重大成果,期待早日正式运行,提高中国射电天文整体的实力。

北京大学天文系徐仁新教授表示,除了科学意义外,毫秒脉冲星还有潜在的应用价值。FAST参与毫秒脉冲星的发现将为全球科学家和工程师提供更好的机遇。

澳大利亚科工组织研究员,国际引力波联合探测委员会(GWIC)成员G. Hobbs表示,国际射电天文界为FAST已经取得大量脉冲星发现感到兴奋,看好FAST的国际合作前景,并期待FAST为引力波探测作出贡献。

FAST将继续调试,以期达到设计指标,通过国家验收,并成为世界一流的射电天文望远镜。

新发现的毫秒脉冲星PSR J0318+0253位置和积分脉冲轮廓。(左图)PSR J0318+0253所在伽马射线巡天图像的位置;(右图a)FAST一小时跟踪观测获得的射电波段积分脉冲轮廓;(右图b)折叠Fermi-LAT累积9年数据所获得的伽马光子积分脉冲轮廓。