1. An ultra low mass and small radius neutron star in 4U 1746-37?
FAST Pulsar Symposium 3 
An ultra low mass and small radius neutron star in 4U ?
Zhaosheng Li
(李兆升)
Peking University
Shanghai

2. Equation of States
Self-bound or
Gravity bound

3. Mass Main sequence NS binaries WD-NS binaries DNS binaries
Black widow pulsar
X-ray/Optical binaries
Anna Watts et al.2014

4. X-ray burst
What is X-ray burst?
Neutron Stars
LMXB

5. Type I vs. Type II
MXB
Rapid Burster
Sala et al.2012

6. Nuclear vs. Gravitational Energy

7. Nuclear vs. Gravitational Energy
Galloway et al. (2008b)

8. Burst Spectra
A burst from 4U

9. PRE in X-ray Burst Photospheric Radius Expansion
Expansion->Contraction->Cooling
The radiation pressure is larger than the
gravitational one.
Photospheric layers are lifted off the surface by the radiation pressure. 4U
Guver et al. 2012

10. Questions Eddington luminosity in PRE bursts? Color correction factor
Geometry effects in Dipping Binaries

11. PRE as standard candles?
Kuulkers et al. 2003

12. Eddington Luminosity?
Guver et al. 2012b

13. Burst Spectra
A burst from 4U

14. Color Correction Factor
Componization
Diluted blackbody
London et al. 1986

15. Color Correction Factor
Guver et al. 2012a

16. Dipping/Non-Dipping LMXBs
High/Low-inclination angle
Peak flux
Touchdown flux
Galloway et al. 2008

17. Galloway et al. 2008

18. Geometry effects
Obscuration or Reflection
Galloway et al. 2008

19. Some relations in PRE bursts
The observed luminosity
Radiation pressure balances gravity

20. Mass and Radius of NS Touchdown Flux & apparent area
Özel et al. (2006，2009, …)

21. 4U
Globular Cluster NGC 6441
dipping binary
EXOSAT & RXTE Obs.

22. Touchdown flux
Very low flux
EXOSAT obs.
Sztajno et al.1987

23. RXTE Obs.
Low touchdown flux (luminosity)
Low mass NS

24. Cooling area

25. Mass-Radius confidence intervals
Bayes
or Monte-Carlo simulation

26. Results
Reflection & Obscuration

27. Conclusions An extremely low mass NS may exist in 4U 1746-37
Reflection
Obscuration
EoSs can be effectively tested from low mass NS
Formation
Lower limit mass (self-bound or gravity bound NS)
Radius