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Quark star RX J1856.53754 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)
M
(Neutron star)
R
Courtesy of K. Iida
Two temperature model
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
QCD coupling constant
where
Energy density
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 pressuredependent 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
4
B ~ (200MeV).