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

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

Introduction Recent deep Chandra LETG+HRC-S observations of RX J1856.5-3754 reports, Drake et al., ApJ. 572 (2002) 996-1001 Black body of X-ray luminosity, Radiation radius

Distance toward RX J1856.5-3754 Drake et al., ApJ. 572 (2002) 996-1001

Spectra of RX J1856.6-3754 Drake et al., ApJ. 572 (2002) 996-1001

The 3σequivalent width upper limit to line features Drake et al., ApJ. 572 (2002) 996-1001

XMM-Newton observation V. Burwitz et al, astro-ph/0211536

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

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

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

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

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

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

Bag model parameters fitted to hadron mass spectra Kohri, Iida and Sato, arXiv:astro-ph/0210259

Energy per baryon (αｃ＝0）

Energy per baryon (αｃ＝0.6）

Equation of state

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

Mass of quark star

Radius of quark star

Mass-radius relation

Mass-radius relation

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

Contours of upper limit of mass

Effects of the pressure-dependent bag constant Generally, we can parameterize the EOS as A ~ 3 -- 4, 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!

Contour of the effective bag constant

Contours of the upper limint of the mass

Conclusion ・We have systematically computed mass-radius relation of quark star within the bag model. ・ Assuming that RX J1856.5--3754 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