Sub-millisecond radio pulsars

Transcription

1 Sub-millisecond radio pulsars Renxin Xu ( 徐仁新 ) Astronomy Department, School of Physics, Peking University China-US Bilateral Workshop on Astronomy Sleeping Buddha Hotel, Beijing April 22, 2008

2 Summary Introduction: PSRs & Spin Activity of subms-psrs To find a subms-psr Conclusions

3 Why to focus on pulsars? Important object! PSR = NS PSRs are spinning NSs Peculiar astro-lab for testing phy-law Strong gravity Strong EM force Supranuclear ρ Precision clocks to be very useful Measure GW, M, Time standard Navigation

4 What s s the nature of pulsars? Speculations v.s. The truth NSs = (normal) NSs + Quark Star F. Weber: Prog.Part.Nucl.Phys. 54 (2005) 193 Quark stars

5 The nature of pulsars depends on physics of matter at supranuclear density which is still uncertain!

6 Observational Evidence for NSs or QSs? To explain observational features in these two kinds of models

7 How to find clear feature to distinguish NSs and QSs? Whether or not PSRs could rotate at sub-millisecond periods? subms-psrs Subms-PSR would be solid evidence for quark stars!

8 Milestones in detecting PSRs faster and faster Only possible in QS model! Spin frequency Keplerian frequency (Mass-shedding limit) Stable axis-symmetric spin (GW radiation) P ~ 1s (1967) P = 0.5ms (1989)? Sub-ms periods (P < 1 ms) P = 33ms (1968) Crab P = 1.6ms (1982) PSR 1937 SN 1987A P = 0.89ms (2007)? XTE 1739 P = 1.4ms (2006) PSR 1748

9 Minimum period of stable uniform rotating for causal EoSs, with good precision, is given by an empirical formula: Haensel et al. (1995) P min (EoS) 1/2 stat R M M (EoS) stat M max (EoS) 10km max 0.82ms A QS with P < P min is possible because of low M and R! Could super-kepler spin be possible for QSs? P Kepler = 0.5 M 1-1/2 R 6 3/2 ms ~ 0.6ms for gravitationally confined NSs! For self-binding QSs High-T QGP in terrestrial experiment RHIC sqgp (2004) super-kepler? 3/2

10 Mass-Radius relation and spin limit QSs can be very light & small, while NSs can not. To identify a quark star in reality? Lattimer & Prakash (2004) ~2M ~10km 0.2 M

11 Summary Introduction: PSRs & spin Activity of subms-psrs To find a subms-psr Conclusions

12 Rotation powered subms-psrs PSRs: : low activity Total spindown power: d 1 2 ~ 2 ~ 5 d 2 I Ω = t I ΩΩ MR ΩΩ R ΩΩ subms-psrs with same dω/dt could be ~10-4 that of mspsrs, if R ~ 1 km (M~10-3 Msun). Subms-PSRs are very low active in their magnetosphere. Their radio luminosity would be much lower than that of mspsrs if the η-coefficient is the same. More sensitive radio telescope is necessary!

13 Radio luminosity: normal-psrs vs. ms-psrs L 1400 : L at 1400 Hz ζ (dp/dt)/p 3 relevant to charge : normal PSRs : mspsrs, P<15ms Subms-PSRs? The reason that we have still not detected Xu et al. (2006) radio sub-mspsrs?

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15 Magnetospheric activity of submspsrs

16 Summary Introduction: PSRs & spin Activity of subms-psrs To find a subms-psr Conclusions

17 Observation of radio pulsars FFT P-search DM-search P- DM ( ) low high dt = 4 10 ν ν DM De-dispersion Sensitivity: S min CT ( sys + Tsky) = G Nt Δν pint Data: Huge W P W

18 To find submspsrs by FAST? Five hundred meter Aperture Spherical Telescope

19 What if a submspsr is found? Pulsars should be a special kind of NSs (QSs!) if discovering P < 0.8 ms. Understand more about Nature: formation-origin, cosmic evolution Higher precision of PSR timing: σ TOA Tsys PW ( / P) t Δν S int mean 3/2 GWR background detection Time standard based on PSR timing

20 Summary Introduction: PSRs & spin Activity of subms-psrs To find a subms-psr Conclusions

21 Conclusion To find a submillisend PSR is clear evidence for quark stars. If successful, it will certainly improve our understanding of the elementary strong interaction between quarks. Because of low masses, the radio luminosity of subms-psrs should be low, but X-ray pulsation may be significant for detection. To search submspsrs is supposed to be one of the key projects in the future FAST program.

22 Thanks a lot and hope to receive your comment-suggestion Any time r.x.xu@pku.edu.cn