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 1746-37? Zhaosheng Li (李兆升) Peking University Shanghai 2014-7-3

Equation of States Self-bound or Gravity bound

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

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

Type I vs. Type II   MXB 1730-335 Rapid Burster Sala et al.2012

Nuclear vs. Gravitational Energy  

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

Burst Spectra   A burst from 4U 1728-34

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 1728-34 Guver et al. 2012

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

PRE as standard candles? Kuulkers et al. 2003

Eddington Luminosity? Guver et al. 2012b

Burst Spectra   A burst from 4U 1728-34

Color Correction Factor Componization Diluted blackbody London et al. 1986

Color Correction Factor Guver et al. 2012a

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

Galloway et al. 2008

Geometry effects Obscuration or Reflection Galloway et al. 2008

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

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

4U 1746-37 Globular Cluster NGC 6441 dipping binary EXOSAT & RXTE Obs.

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

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

Cooling area

Mass-Radius confidence intervals Bayes or Monte-Carlo simulation

Results Reflection & Obscuration

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