1. Quark star RX J1856.5-3754 and its mass
Kazunori Kohri
　　　（郡　　和範）
RESCEU, Univ. of Tokyo
K. Kohri, K. Iida and Katsuhiko Sato,
Prog. Thor. Phys. 105 (2002) in press

2. Contents ・ Introduction ・ Observations of RX J1856.5-3754
・　　Two-temperature model?
・　　Quark matter in bag model
・　　Quark star
・　　Systematic study of mass of the star
in bag model
・　　Other constraint on mass of the star
・　 Other theoretical model of quark matter
・　 Conclusion

3. Introduction
Recent deep Chandra LETG+HRC-S observations of RX J reports,
Drake et al., ApJ. 572 (2002)
Black body of
X-ray luminosity,
Radiation radius

4. Distance toward RX J
Drake et al., ApJ. 572 (2002)

5. Spectra of RX J
Drake et al., ApJ. 572 (2002)

6. The 3σequivalent width upper limit to line features
Drake et al., ApJ. 572 (2002)

7. XMM-Newton observation
V. Burwitz et al, astro-ph/

8. RX J1856.5-3754 is quark star? i) No pulsation
ii) No spectral features
iii) Small radiation radius

9. Mass-radius relation of compact star
(Quark star)
(White dwarf)
(Neutron star) M R
Courtesy of K. Iida

10. Two temperature model Cold with heavy-element atmosphere
F.Walter and J.Lattimer, ApJ (2002)
T.M. Braje and R.W. Romani, ApJ (2002)
X-ray
Hot
Cold
UV/Optical
Hot
X-ray

11. Broad band spectral fit in two-temperature blackbody
T. Braje and R.W. Romani, ApJ (2002)

12. Quark matter (zero-temperature uds quark matter)
Thermodynamic potential
Energy density
QCD coupling constant
where
Strange quark mass
Bag constant

13. Quark matter-2 Number density Pressure Baryon number Conditions
In equilibrium through weak interactions
Charge neutrality

14. Bag model parameters fitted to hadron mass spectra
Kohri, Iida and Sato, arXiv:astro-ph/

15. Energy per baryon
(αｃ＝0）

16. Energy per baryon
(αｃ＝0.6）

17. Equation of state

18. Quark star Equation of hydrostatic equilibrium
(Tolman-Oppenheimer-Volkoff (TOV) equation)
Equation of mass conservation
Then, the radius is determined by
The mass is

19. Mass of quark star

20. Radius of quark star

21. Mass-radius relation

22. Mass-radius relation

23. Observed X-ray luminosity
Bondi accretion rate
where,
Then,

24. Contours of upper limit of mass

25. Effects of the pressure-dependent bag constant
Generally, we can parameterize the EOS as
A ~ , for Lattice data , Peshier,Kampfer,Soff (2001).
A ~ 2, for Relativistic Mean Field, Dey et al. (1998) etc.
Then, we transform it into
where
Namely, inside the star the bag constant effectively becomes large!

26. Contour of the effective bag constant

27. Contours of the upper limint of the mass

28. Conclusion
・We have systematically computed mass-radius relation of quark star within the bag model.
・ Assuming that RX J is a pure quark star, we have derived an upper limit on its mass.
・ We find the upper limit can amount to 1 M around
B ~ (200MeV). 4